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siliconchip.com.au
Celebrating 30 Years
December 2017 1
Catalogue Sale 24 November - 26 December, 2017
To order phone 1800 022 888 or visit www.jaycar.com.au
Contents
Vol.30, No.12; December 2017
SILICON
CHIP
www.siliconchip.com.au
Features & Reviews
14 Rail Guns and Electromagnetic Launchers
Using electromagnetic force instead of explosives or steam can launch aircraft
off the deck of a carrier, fire a shell without the need of a warhead . . . or
perhaps one day even launch satellites – by Dr David Maddison
34 Interfacing with the Raspberry Pi – for Beginners
It’s one of the world’s most popular micro computer platforms – but even
many long-term “Pi” users don’t realise that its GPIO port can deliver so much
flexibility. We say it’s for beginners . . . of all levels! – by Andrew Pullin
57 Review: Music Hall mmf-1.3 Belt-Driven Turntable
It’s unusual to find a quality turntable offering 78 RPM as well as the “normal”
33.33 and 45 RPM speeds. With the increasing interest in vinyl (and shellac!)
discs in recent years, we thought it worth a close look – by Leo Simpson
78 El Cheapo Modules 11: Pressure/Temperature Sensors
Two tiny modules which sense barometric pressure and air temperature and
send their readings to virtually any micro via a standard I2C serial interface. We
were so impressed we made them into a project (see below!) – by Jim Rowe
Constructional Projects
24 Touchscreen Altimeter and Weather station
Based on low-cost modules and the mighty Micromite with Touchscreen
BackPack, this accurate altimeter also has built in weather reporting. Even if
you don’t fly, it’s a fascinating and worthwhile project – by Jim Rowe
42 The Arduino MegaBox from Altronics
Build your Arduino design into a professional finished case – plug in an Arduino
UNO or Mega and shield. In addition, it has provision for a 16x2 LCD, four control
buttons, an IR receiver and a rotary encoder on the front panel – by Bao Smith
66 Build your own Super-7 AM Radio Receiver – Part II
This month we’re putting it together and then showing you how to align your
Super-7 AM Radio Receiver. Fit it into the smart, laser-cut acrylic case and
you’ll have a project that really will turn heads! – by John Clarke
84 Finishing our new 6GHz+ Digital Frequency Meter
It’s caused quite a stir since we introduced this remarkable instrument back in
October. Here in part III we tie up all the loose ends and explain how to get the
most from it – by Nicholas Vinen
Your Favourite Columns
60 Serviceman’s Log
Video trials and tribulations – by Dave Thompson
90 Circuit Notebook
(1) Four quadrant power supply based on high voltage op amp
(2) Micromite-based air conditioner remote control
94 Vintage Radio
Roberts R66 4-valve 2-band portable – by Marc Chick
Everything Else!
2 Editorial Viewpoint
4 Mailbag – Your Feedback
88 SILICON CHIP Online Shop
98 Ask SILICON CHIP
siliconchip.com.au
siliconchip.com.au
103 Market Centre
104 Advertising Index
104 Notes and Errata
Celebrating 30 Years
Celebrating 30 Years
Electromagnetic rail guns are
already used to launch aircraft from
carriers and fire massive shells
without even needing a warhead. We
look at the latest developments and
the future possibilities – Page 14
Even if you never fly anything,
our new Micromite Touchscreen
BackPack-based
Altimeter and
Weather
Station makes
for a really
interesting – and
fun – project. It’s very
accurate, too – Page 24
There’s a lot more to the Raspberry
Pi 3 GPIO (General Purpose Input/
Output) than
most users
realise!
Here we
look at it
in detail –
Page 34
Why on earth would you want
to build an AM Radio Receiver?
Because you CAN –
and it looks
as good as
it performs
(especially
in its custom
laser-cut
acrylic case!)
– Page 66
If you only build one piece of test
gear this year (or next!) make it the
outstanding 6GHz(+) touchscreen
DFM (digital
frequency meter).
With the best
performance
we’ve ever
seen, it should
be on every test
bench – Page 84
Our cover photo: Christian Moullec flying with geese
© Superbass / CC-BY-SA-3.0 (via Wikimedia Commons)
December 2017 1
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SILICON
SILIC
CHIP
www.siliconchip.com.au
Publisher
Leo Simpson, B.Bus., FAICD
Editor
Nicholas Vinen
Technical Editor
John Clarke, B.E.(Elec.)
Technical Staff
Ross Tester
Jim Rowe, B.A., B.Sc
Bao Smith, B.Sc
Photography
Ross Tester
Reader Services
Ann Morris
Advertising Enquiries
Glyn Smith
Phone (02) 9939 3295
Mobile 0431 792 293
glyn<at>siliconchip.com.au
Regular Contributors
Dave Thompson
David Maddison B.App.Sc. (Hons 1),
PhD, Grad.Dip.Entr.Innov.
Geoff Graham
Associate Professor Graham Parslow
Ian Batty
Cartoonist
Brendan Akhurst
SILICON CHIP is published 12 times
a year by Silicon Chip Publications
Pty Ltd. ACN 003 205 490. ABN 49
003 205 490. All material is copyright ©. No part of this publication
may be reproduced without the
written consent of the publisher.
Subscription rates: $105.00 per year
in Australia. For overseas rates, see
our website or the subscriptions page
in this issue.
Editorial office:
Unit 1 (up ramp), 234 Harbord Rd,
Brookvale, NSW 2100.
Postal address: PO Box 139,
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Phone (02) 9939 3295.
E-mail: silicon<at>siliconchip.com.au
Printing and Distribution:
Derby Street, Silverwater, NSW 2148.
ISSN 1030-2662
Recommended & maximum price only.
2
Silicon Chip
Editorial Viewpoint
Australia’s strength in manufacturing
The recent closure of the Holden plant in Elizabeth,
Victoria, rightly received a lot of media attention. The
end of Australian mass-market automotive manufacturing
(with the Toyota and Ford plants having already closed)
is undoubtedly a disruption to the Australian economy,
with a large personal impact on those who have had to
find new jobs.
It is likely to have an impact on our local electronics
manufacturing industry too. The vehicles made in the
now-closed plants contained up to 70% locally-made parts – a lot of it involving electronics.
Hopefully, those suppliers will be able to continue operation as there are still
companies making specialised vehicles for the mining industry, the military and
off-road market. As well, many of those suppliers are active overseas.
But there is another reason why we’ve mentioned the automotive plant closures; they echo the closures of large consumer electronics factories in Australia,
following the abrupt tariff reductions by the Whitlam government in 1975. Prior
to that time, virtually all consumer electronics products, such as radios, stereograms, TVs and car radios, along with all whitegoods were protected by high
tariff walls. They have all gone – the last locally-built fridge was made quite
recently, with the Electrolux factory in Orange, NSW closing in November 2016.
One of the largest radio and TV manufacturers in Australia, AWA, shut down
its last factory in the early 90s. And they didn’t just put together electronics from
parts made overseas either. From the 40s to the 70s, when local manufacturing
was strong, just about all the electronic components parts were made in Australia and in many cases, in the same factory as final assembly took place. Those
halcyon days, when consumer electronics products were a great deal more expensive than today, are long gone.
But Australia today still has a substantial electronics industry and it is lean
and efficient, as it has to be to compete on world markets. Areas where Australian electronics manufacturers find success include mining tools, medical equipment, sound reinforcement, traffic control, industrial process control and more.
And many of these companies are well-regarded around the world and in many
cases are market leaders.
You may also be unaware that there are at least 20 electronics assembly facilities in Australia, some of them large and using advanced technology.
Don’t believe us? In New South Wales alone we’re aware of Circuitwise, GPC
Electronics, Nesstronics, Pritchard, On-Track, Soltronico and Wavetronics. In Victoria there’s Alfatron, Duet Electronics, Extel and Sniper Electronics; Queensland
has Circuit Solutions, Crystalaid, Hetech, Masters & Young and RFTech; South
Australia has Entech and TCM Electronics while in Western Australia there’s
Advanced Technology & Manufacturing, Lyntel and PCB Assembly. These companies would only exist if they had a significant number of customers. And that
doesn’t include the Australian-based design houses which have their equipment
fabricated off-shore.
Successful Australian electronics manufacturers include Aldridge Traffic Systems, Blackmagic Design, Codan, Exablaze, Metamako, Radixon, Redarc, Redback Audio and Vix Technology.
And let’s not forget companies like Melbourne-based Versatile Technology,
(featured in our January 2016 issue). The equipment they design and make for
testing drink bottles and cans is exported worldwide.
Undoubtedly, there are many more Australian electronics companies, large
and small, which we don’t hear about, which are not only providing employment but contributing strongly to our GDP.
You won’t hear about them in local media but they are out there, doing well
while competing in a very tough environment.
Nicholas Vinen
Celebrating 30 Years
siliconchip.com.au
MAILBAG – your feedback
Letters and emails should contain complete name, address and daytime phone number. Letters
to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and
has the right to reproduce in electronic form and communicate these letters. This also applies to
submissions to “Ask SILICON CHIP”, “Circuit Notebook” and “Serviceman”.
Congratulations for
30 Years of Silicon Chip
I have just read Ross Tester’s review
of Silicon Chip’s last 30 years and was
particularly interested in the circumstances that led to the foundation of
your publication.
During my 30-year experience as
Australian Engineering Manager and
global engineering consultant for BP
Solar, I found an abundance of stupidity and arrogance in large corporations,
particularly within British Petroleum.
Your outstanding success in Australian and global electronics publishing warms my heart. I still have fond
memories of working with Leo Simpson, Jim Rowe, Bob Flynn and others,
during my short stint with Electronics
Australia, prior to April 1970. Wishing you every future success.
Anthony Leo,
Cecil Park, NSW.
Details of the radars used
to track WRESAT
I read the article you published on
WRESAT in the October issue (www.
siliconchip.com.au/Article/10822)
Birthday wishes from our
biggest supporter
Dear Leo & Silicon Chip staff,
On behalf of all at Jaycar, I would
like to congratulate you on the 30th
anniversary of your first issue. That
milestone seems to have snuck up!
I can remember like it was yesterday when you first started. I had no
doubt that you would be successful
and Jack O’Donnell (owner of Altronics) felt the same.
And yes, the magazine has seen
a profound change in the way the
world works. You actually started
before the rise of the internet but
now almost everything works within its context.
I still look forward to my monthly
read of “Silicon Chip” for despite
everything else, I am still an electronic enthusiast and do appreciate
the clarity of the text, illustrations
4
Silicon Chip
and thought you might like to take
a look at two related pieces which I
authored. They are located on Colin
Mackellar’s Honeysuckle Creek tracking station site.
The first describes the AN-FPS16
radar which was mentioned in the
WRESAT article and is found at www.
siliconchip.com.au/link/aaga Once
this page loads, click on the link titled
“About the FPS-16 Radar”
The second article describes the ANFPQ6 radar at the Carnarvon tracking station and is located at www.
siliconchip.com.au/link/aagb Click
on the link titled “The FPQ6 radar”.
There is a description by Hamish
Lindsay; scroll down to find the description of the radar I wrote.
Ken Anderson,
Sale, Vic.
a 1pps (one pulse per second) output.
But there is a different version of the
Neo-7M module that does provide a
1PPS output.
It is available from eBay and sells
for US$7.85. See: www.ebay.com/
itm/311876309386 In addition to an
SMA input port for an external active
antenna, this module has a passive antenna mounted on the rear of the PCB.
It also has a micro-USB interface (in
addition to UART connections).
Using the external antenna port, the
sensitivity seems to be better than the
Neo-6M module that I have.
Trevor Woods,
Auckland, NZ.
Neo-7M module
with 1pps output is available
Limiting water heater power
for solar installation
I am writing regarding your October
2017 El Cheapo Modules article on the
two GPS receivers (siliconchip.com.
au/Article/10827). It indicates that the
u-blox Neo-7M module does not have
and diagrams that you work so hard
to keep to a high standard.
Once again, a note of thanks from
all of us at Jaycar. Cheers!
Gary Johnston,
Managing Director,
Jaycar Electronics Group.
Did we forget to mention
someone important?
I just received my November copy
of Silicon Chip today and noted the
reason for well-deserved celebrations. Congratulations on achieving
30 years of quality publication and
outstanding technical journalism
over what must have been some very
difficult patches.
I noted that your editorial did not
mention Jim Rowe for some reason.
I trust he is in good health and the
lack of any special mention was just
a simple editorial slip-up! Wishing
Celebrating 30 Years
I have a suggestion regarding the
question titled “Limiting hot water
power to suit solar system” in the Ask
Silicon Chip section of the October issue, on page 96.
you all the best for the future…
Owen Hill,
Rutherford, NSW.
Leo responds: Jim Rowe is alive and
kicking and working full-time for
Silicon Chip. In fact, Jim has worked
for Silicon Chip virtually since EA
folded – I did not want his know-how
to go to waste.
Of course, other past EA staffers
worked for Silicon Chip in the early
years, including ex-editor Neville
Williams, ex-assistant editor Philip
Watson, and in more recent years,
Maurie Findlay (all now deceased).
More recently we have had our
Induction Motor Speed Controller
(2012) designed by past EA-staff
member Andrew Levido and other
staff members have made smaller
contributions. Finally, Ross Tester
also worked at EA in the past and
came to Silicon Chip in 1995.
siliconchip.com.au
One way of using your limited power to boost your hot water is to use a
twin element hot water tank.
The bottom element can be left asis but the top element can be replaced
with a 2kW element which can be
run from solar power during the day,
when sun shines. When the sun does
not shine, a contactor could be used
to connect it back to the mains.
David Haddock,
Bethania, Qld.
Note: Not all hot water tanks have
booster elements but many do have
provisions for such an element.
Preventing corrosion in
solar-boosted hot water systems
Thanks for your articles about connecting your solar panels to an electric
hot water tank. The most recent article left me with the impression it was
too hard to do as over time a DC current would result in corrosion of the
electric element, an AC supply being
required to prevent this.
The frequency of 50Hz alternating
current is arbitrary. Would a 1Hz supply work? What about simply swapping the polarity of the DC at the end
of each day?
Does anyone have any knowledge
on the most effective period to prevent
corrosion? I might try it on my kettle
as I don’t think its any different to an
electric hot water tank.
Hamish Rouse,
Mt Martha, Vic.
Response: you are quite right that the
polarity doesn’t need to reverse at
50Hz. However, the problem with a
24-hour period is that the total current flow from one period to the next
could be quite different, meaning that
you could still have a DC current flow
on average. Also, it’s possible that too
much corrosion could occur in a 24hour period for it to easily be reversed
in the next 24-hour period.
So we would suggest a shorter period
than this, although 1Hz would probably be OK, or even a somewhat lower
frequency. A relay swapping the element polarity every few minutes would
probably do the trick but you would
have to make sure the relay could handle switching the (potentially) high DC
current or it wouldn’t last long.
Serviceman story a reminder of a nice,
easy repair
I liked the Serviceman story regarding the repair of a MIG welder.
Some time ago, I needed an AC TIG
welder to weld aluminium. These
things are not cheap but I found a second-hand unit in the Hunter where
the AC function had failed but the DC
function (for welding steel) was still
working. I bought it thinking that it’s
only electronics so it should be easy
to fix.
Getting it back to Canberra I opened
it up to start the repair. I couldn’t see
most of the control board (with TTL
components) for all the grinding dust.
I blew out the unit with compressed
air. I then tested it again and the AC
function worked. It was the simplest
electronic repair I have ever done!
Garry Woods,
Canberra, ACT.
BackPack problems may
be due to bad LCD pin connections
I just read the letter titled “Pain in
the BackPack” from M. L., on page 97
of Ask Silicon Chip, in the October
2017 issue. I had the same problem
after building the Micromite Plus LCD
BackPack kit.
In my case, it was caused by a faulty
through-hole connection on the PCB at
the CON3 LED pin. The solution was
to solder the pin on the top side, after cutting away a little of the socket
strip plastic.
I then also found the touch feature
didn’t work. This turned out to be the
same problem and was cured with the
same fix on the CON3 T_CLK pin.
Playing around with the Micromite
has been a great learning experience.
I also had a problem getting stable
analog input readings (from a thermistor via a resistive voltage divider).
Adding an RC low-pass filter at the input didn’t help.
Replacing the 5V switchmode supply with a linear 5V regulator fed from
12V battery only made a small improvement. Increasing the LCD backlight switching frequency from 200Hz
to 2000Hz greatly reduced the noise.
www.okw.com.au
www.okw.com.au
TO EACH HIS OWN HOUSING
ROLEC OKW
OKW
ROLEC
Australia New
New Zealand
Zealand Pty
Pty Ltd
Ltd
Australia
Unit 6/29
6/29 Coombes
Coombes Drive,
Drive,
Unit
Penrith NSW
NSW 2750
2750
Penrith
Phone: +61
+61 22 4722
4722 3388
3388
Phone:
E-Mail: sales<at>rolec-okw.com.au
sales<at>rolec-okw.com.au
E-Mail:
siliconchip.com.au
Celebrating 30 Years
December 2017 5
Want to work
for Australia’s
Electronics Magazine
If you live, breathe and sleep electronics you could be just the person we’re
looking for. While formal qualifications
are well regarded, don’t let a lack of letters after your name put you off, if you
have the experience we’re looking for.
The right person will certainly have
skills in the following areas:
Analog and digital circuit design from
concept to completion
Circuit analysis and debugging
PCB layout (we use Altium Designer)
PC software development and
embedded programming
Operating electronic test
equipment
Mechanical design
But most of all, you’ll have the ability
to write interesting articles (in English)
describing what you’ve built and how
SILICON CHIP readers can reproduce what
you’ve done. You will have seen the style
of SILICON CHIP articles – you’re almost
certainly an existing SILICON CHIP reader.
If you have skills in other areas which
would help SILICON CHIP appear each
month, tell us about them too: skills such
as sub-editing, desktop publishing/layout, circuit drawing, photography, image
processing, technical support/customer
service (via telephone), project management, parts ordering and management,
database administration, website design/programming and operating CNC
equipment.
We don’t expect you to have all these
skills – but we’ll help you to develop them
as required.
You’ll need to be highly self-motivated
and able to work well by yourself as well
as in a small team. Being able to work
to the rigorous deadlines of a monthly
magazine is vital.
Candidates will be given a six-month
trial with a permanent position at the successful conclusion.
If you think you have what it takes,
email your resume/CV (along with contact
details!) to silicon<at>siliconchip.com.au
6
Silicon Chip
Perhaps digital currents are adding
noise to analog AVDD or AVSS (IC1
pins 19 & 20). Increasing the capacitor
value between these pins from 100nF
to 10µF and soldering a wire to each
end of it to provide analog power and
ground to the thermistor’s resistive
voltage divider totally cured it.
On the next Micromite PCB revision, similar analog power and ground
header pins could be added. Also,
the PCB design methods you use for
your outstanding audio amplifiers
may help.
A temporary software solution is to
read the analog input many times and
take the average. It slows things down
but it works. For example:
SETPIN 22, AIN : SETPIN 23, AIN :
SETPIN 24, AIN
PRINT AnalogSample(22),
AnalogSample(23),
AnalogSample(24)
FUNCTION
AnalogSample(InputPin)
LOCAL Vin = 0
LOCAL INTEGER Sample
For Sample = 1 to 1000
Vin = Vin + Pin(InputPin)
Next
‘multiplication faster than division
AnalogSample = Vin * 0.001
EndSub
Response: soldering the pins on the
top layer of the board should not be
necessary and this suggests a failure
of the through-hole plating which is
not good.
Modern PCB quality is high and
we’re very surprised to hear of this
kind of manufacturing fault, especially
since most PCBs now go through an
electrical testing procedure before they
are sent out.
As you’ve discovered, the only way
to reduce analog reading noise to
a reasonable level is to connect the
analog sensor grounds directly to the
AGND pin.
Since this is internally connected to
digital ground in the PIC chip, we can’t
run separate analog and digital ground
tracks. The Backpack is a general purpose board so compactness was prioritised over analog reading accuracy.
It would be a good idea to have a
separate analog ground connection on
microcontroller boards. But generally
speaking, if you need accurate measurements, it’s easier to connect a separate analog-to-digital converter board
Celebrating 30 Years
to the PIC via an SPI bus and this will
not only allow you to separate out the
digital noise but it will likely also provide better resolution and more inherent accuracy.
For example, breakout boards for
the AD7793 24-bit low-noise ADC are
available for less than $10 and offer
much better performance than the
typical 10-bit ADC in a PIC.
Useful tip gleaned from Serviceman
I was just reading the Serviceman’s
Log the other day and Dave’s tip about
cutting the slot in the Torx bit, in order
to remove a recessed screw, proved to
be very useful.
My pressure cleaner was leaking and
I wanted to dismantle it to see what the
problem was, so Dave’s tip solved the
issue of the three inaccessible screws.
Unfortunately, the pressure cleaner
is a write-off, due to the specialised
parts being unavailable but at least I
was able to find what the problem was.
I have already emailed him and told
him how useful his suggestion was.
Has Leo stepped down as Editor, or
is he just on long service leave? He’s
been the Editor of Silicon Chip since
day one and it’s a bit different seeing
Nicholas as Editor.
I’ve been collecting Silicon Chip
magazines over the last few years and
I think I now have almost all the issues, although I still have some issues
to check for missing pages.
However, I have not been able to
find a copy of the February 1988 issue.
Hopefully, one will show up sometime, but it could be rare now.
Bruce Pierson,
Dundathu, Qld.
Response: If you check page two of the
January 2017 issue, you will see that
Nicholas has been listed as the Editor
for some time now.
Leo Simpson is still the Publisher
although it remains to be seen how
much longer he will stay in that role.
If you look up the date of his early
articles in Electronics Australia (in
1967), you will see that he has been in
the magazine business for a long time!
Unfortunately, while we keep back
issues in stock for some time, we tend
to discard them after about 20 years
due to minimal demand.
The earliest back issue that we
have in stock is January 1997. We imagine quite a few readers would still
have a copy of the February 1998 issue though.
siliconchip.com.au
Silicon-Chip--Future-Products.pdf
1
4/29/16
10:59 AM
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siliconchip.com.au
Celebrating 30 Years
December 2017 7
Helping to put you in Control
UniPi Neuron S103 PLC
UniPi Neuron S103 is a
universal control unit. Based
on the popular Raspberry Pi
3 model B it features 4 DI,
4 DO, 1 AI, 1 AO and a 1
wire interface.
SKU: UPC-001
Price: $289.95 ea + GST
UniPi 1.1 starter set
A Raspberry Pi 3 B
board fitted with an
industrial grade I/O
expansion board.
Together they form
a programmable
control unit for universal use in automation,
regulation, and monitoring systems.
SKU: UPC-075
Price: $269.95 ea + GST
Atmospheric Temperature &
Humidity Sensor
Wall mountable with radiation
shield. Range: -40~60°C and
0-100%RH. RS485 Modbus RTU
output.
SKU: RKS-113
Price: $259.95 ea + GST
Ethernet Digital IO
Voltage, Temperature,
Humidity Alarm and
Control. This item is an
Ethernet control unit
with 4 digital inputs, 4
relay outputs, 4 analogue
inputs and a 1-Wire
interface for up to 8 x 1-Wire sensors.
SKU: TCC-025
Price: $279.00 ea + GST
Breakout Board
The MCP4725 is an I2C controlled Digitalto-Analog converter (DAC)
and this little board makes it
easy to use on a breadboard
in your projects.
SKU: SFC-008
Price: $7.10 ea + GST
Din Rail Power Supply
DRC-100B is a 27.6V 100W
Din Rail Power Supply
with Battery Charger (UPS
function). Provides AC Fail
and low battery alarms.
SKU: PSM-1172
Price: $102.60 ea + GST
LabJack USB Data Acquisition Module
The most economical
member of the LabJack
family, the U3-HV has 12
flexible I/O, 4 HV analog
inputs (12 bit -10 to 20
VDC), 2 voltage outputs
and USB interface.
SKU: LAJ-022
Price: $192.00 ea + GST
For Wholesale prices
Contact Ocean Controls
Ph: (03) 9782 5882
oceancontrols.com.au
Prices are subjected to change without notice.
8
Silicon Chip
NBN modem rebooter circuit was
unnecessarily complex
Following the recent publication of
the automatically rebooting NBN modem in the Circuit Notebook section of
Silicon Chip, September 2017 (www.
siliconchip.com.au/Article/10785).
Please see above a picture of my lowtech device that does the same thing.
It too de-powers the NBN modem at
3:00am each morning but it doesn’t repower it until 15 minutes later.
This is a disadvantage compared to
your published design but I can live
with the 15-minute downtime at that
time of the morning. My approach has
no Micromites, no SMDs, no firmware,
no software and is ultra-reliable.
However, the way things are going
with electricity in this country, neither
approach may be needed much longer.
There may just be enough blackouts to
re-set NBN modems frequently.
Thanks for the great magazine.
Jim McLellan,
via email.
Response: your approach is commendably simple but does have the
disadvantage that the reset time will
change if there is a blackout and you
may not notice it straight away. The
published circuit does at least have a
backup battery.
We agree it’s overly complex for
the job it does but we purposefully
published it as-is since that was the
approach the author took and there
were some interesting aspects to the
design.
November issue enjoyed
Today I received my hard copy edition of this magazine; it’s a great read.
I think the article on Making Phone
Calls via Satellite is awesome. And
Celebrating 30 Years
the 30 years article is great as well –
how the years have gone by!
I still insist on reading the printed
version rather than online. I like to
give my eyes a “digital detox” away
from the screen and read a physical
magazine for a change.
It is certainly a magazine I look forward to receiving in my PO Box once
a month. Thanks again for a great
magazine.
Peter Casey,
West Pennant Hills, NSW.
Comments on Digital Radio Mondiale
and history of AM stereo
As a keen radio and shortwave listener over many years, I found the two
articles on DRM, on pages 61 and 63 in
the September issue of Silicon Chip to
be of great interest (www.siliconchip.
com.au/Article/10797 and www.
siliconchip.com.au/Article/10798).
They brought to mind several debacles in both Australia and New Zealand in the area of broadcasting.
In New Zealand in the 1970s, with
consumer AM/FM receiving equipment becoming available due to small
numbers of imports and overseas travellers returning with portable and hifi
equipment, there was pressure on government to permit the establishment
of FM broadcasting. However, it did
not commence until 1982.
Part of the reason for delaying its
introduction was that the 88-108MHz
band was to a large extent used for the
Land Mobile Service which meant that
a shift of this service to other frequency bands was necessary.
That came with the consequent cost
and delays in implementing the new
base stations and mobile equipment
required.
siliconchip.com.au
What this indicated was a lack of
planning for future changes and public demand and pressure for a service
which existed in many other parts of
the world using this frequency band.
In Australia, 1985 was the year that
AM stereo was introduced. However,
in its wisdom, the government had decided to allow all four systems available to be licensed and let the market
decide on the ultimately successful
system. This was the same strategy
adopted by the FCC in the USA.
The FCC eventually made the Motorola C-QUAM system the standard.
In Australia, AM Stereo was never going to be a success due to the size of
the country with such relatively small
and widely spaced population and
with low quantities of suitable equipment available. So AM stereo here died
a slow death.
As far as the closing of Radio Australia is concerned, yes, it is unfortunate, however, the ABC has been so
starved of funds by successive governments over time that they need to
make every dollar count, especially as
they have to invest in ever-changing
technology in order to remain a leader
in the area of broadcasting.
Nevertheless, I am in support of a
reinstatement of Radio Australia and
the three internal shortwave services.
A different funding model needs to
be found whereby a separate allocation by government for the service is
made available, possibly via the Foreign Affairs and Aboriginal Affairs
departments.
And now looking to the future of
broadcasting. In the case of the expansion of DAB+ services, it would appear from the table on page 62 of the
September 2017 issue that a number
of the regional areas with large populations are not about to have a DAB+
service any time soon.
Canberra and Darwin have had a
trial DAB+ service for some years using Channel 10B, which is now to be
upgraded to a new service using Channels 9A and 9B.
As for the implementation of services using DRM, the ACMA website
states that “DRM is unlikely to be a
viable option in the short to medium
term in Australia as there are only a
few receivers currently available in
the market.
In addition, the prospect of dual
DAB and DRM receivers being introduced into the Australian market is
siliconchip.com.au
low”. So I guess that statement says it
all, it is not under consideration.
Personally, having had experience
of listening to DRM transmissions from
several broadcasters, I must say that
unless the signal-to-noise ratio is good,
the transmission will not be decoded
and the audio will drop out.
This is the case even though the station can still be seen on the waterfall
display and the signal strength meter.
It is sort of like using a mobile phone
in a poor area where the signal just
drops out.
So for now, in my area (the Hunter
Valley), I will continue to use the existing AM and FM stations. The quality of the FM broadcasts is pretty good,
depending on program material and
from what I have, read it may be better than DAB+.
Thank you for an interesting and
thought-provoking publication.
Richard Kerr,
Cessnock, NSW.
Comment: the statement from ACMA
sounds like a chicken-and-egg argument. Of course there won’t be many
radios in Australia capable of receiving DRM if there are no DRM broadcasts.
The same could have been said of
DAB/DAB+ just a few years ago. We
agree with you that good FM stations
can provide better sound quality than
DAB+. The digital compression is just
too severe for it to be hifi.
Nothing new under the sun when it
comes to heating water
I saw your article on adjusting hot
water heater thermostats in the October 2017 issue (www.siliconchip.com.
au/Article/10834).
You may be interested in doing
an article on an Australian company
called Microheat.
They developed and own the patent for an “instantaneous” electric
hot water technology which basically involves zapping the hot water
with electricity. See http://mams.rmit.
edu.au/xogcg47u4b2s.pdf and www.
microheat.com.au/the-technology
Basically, it zaps the water to
30~50°C instantaneously with minimal standby power.
Joseph Goldburg,
Dingley Village, Vic.
Response: That “instantaneous” hot
water heating system is neither new
nor instantaneous. The heating “element” consists of two plates immersed
Celebrating 30 Years
December 2017 9
in the water and the plates have the
full 230VAC applied to them.
The water is heated up as it passes
between the plates. Any heating effect
relies on mineralisation (ie, salts) in
the water to provide some conduction.
Despite the name, it does not use microwave heating. Nor will it work on
water which is very pure or distilled.
So rainwater or water which is very soft
will not be able to be heated effectively
or will take a very long time to heat.
The rate of heating will depend
solely on the amount of heat which
can be pumped into the water and
the rate at which the water passes between the plates.
Unless the metal plates are very
large (and close together) the heating
effect is likely to be slower than in
a tank with a conventional resistive
heating element. Nor is this method of
heating any more efficient than with
resistive elements.
This is not to say that this system
of heating will not work. It clearly will
work but the heating effect will be fairly modest and at low flow rates.
Finally, this system of heating was
used over 70 years ago in electric
jugs. The “element” consisted of two
closely-spaced metal discs. This had
the advantage that the heating element would not burn out if it was not
fully immersed but they were slower
to boil water than jugs with a resistive element.
Printed back issues
take up too much space
I have been buying Silicon Chip for
many years and I am sure like many
other readers have quite a stash of
back issues.
With plans afoot to move interstate
at the end of the year, I have started
the process of looking around the shed
to see what will make the cut into the
moving box. Unfortunately, 15 years
worth of back issues won’t make it.
I do find myself occasionally looking up back issues for old projects, but
not enough to justify keeping them all.
Has there been any thought about digitising the old issues of Silicon Chip
and making the archive available for
purchase?
Circuit Cellar and Elektor both allow
you to purchase a complete archive or
access back issues as PDF files through
the website.
I think this might also be a good way
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upcoming demise of Flash. By having
full PDF issues on the website each
month you remove the need to manage the individual projects.
By adding a digital watermark to
the files you could link them with the
email address of the original purchaser
allowing you to track where they come
from should issues start appearing on
pirate sites.
While I offer the suggestion as
food for though I am currently going
through the process of looking through
each magazine and removing the pages
with any articles of interest with the
intention to scan them and make my
own PDF copy for personal use.
Bill Coghill
Ramsgate, NSW.
Response: we would love to offer PDF
downloads but we lack the resources
to police the already rife copyright violations which cost us money.
Magazine sales are a large proportion of our revenue and without them,
the magazine will fold (no pun intended). We expect that if we offered PDFs,
the problem would just get worse, regardless of watermarking.
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Silicon Chip
Celebrating 30 Years
siliconchip.com.au
Seeing as you are a long-term print subscriber, perhaps
you can take advantage of our subscription upgrade offer
which allows you to get access to all the online issues that
you already have as print issues, at a greatly reduced price.
See the entries listed under “Subscription upgrade
[print to combined]” at the following link for pricing details: www.siliconchip.com.au/Shop/SubRates?show_
upgrade=1
Online issues are available back to May 1997. We suggest you try out the free previews on our website to see if
reading the issues on-screen suits you before paying for
an upgrade.
Hifi Radio Receiver would be appreciated
With reference to the letter “Modern hifi radio receiver
design desired” in the Ask Silicon Chip section of the October 2017 edition of Silicon Chip, I too live in the country
and would be very interested in such a project.
As always I look forward to each edition of Silicon Chip
– it’s an excellent magazine. My particular interest is in
the Micromite projects.
David Hebblethwaite,
Maleny, Qld.
Problem with programmed chips for 50A Charger Controller
I have a need to charge a battery from a vehicle to run
some radio equipment.
I purchased the 50A Charger Controller PCB (November 2016; siliconchip.com.au/Article/10413) and pre-programmed microprocessor from Silicon Chip and the other
items from my local Jaycar store.
12
Silicon Chip
Assembly and checkout went smoothly and I verified
that all components were the correct value. I noticed some
discrepancies between the circuit diagram (Fig.3 on page
35) and the PCB, for example, D4’s cathode actually connects to the battery + terminal, not JP1 as shown on the
circuit.
I’m not quite sure how D4 protects the board if the battery is connected in reverse as either the PCB track will
vaporise or the diode would fail due to over-current.
I powered the unit up using a bench supply for testing
and varied the voltage up and down. I confirmed that pin
6 on IC1 was varying in voltage from 3.2 to 4.5V but neither relay was switching.
I figured it might be a dud microcontroller so I purchased
another one from Silicon Chip and had the same result.
I had a friend check both microcontrollers out but they
seemed to be blank. I then had him download the software from your website and program them. Imagine my
surprise when the unit then worked!
Please check your stock of pre-programmed chips and
confirm that they are really programmed.
Also, the circuit description on page 35 states “it switches on transistor Q1 to activate relay RLY1 and interrupt the
charge” …it should say “it switches OFF transistor Q1 to
deactivate RLY1 and interrupt the charge”.
The circuit also has a flaw in that if the battery
voltage falls below the supply dropout voltage of REG2,
the charger will never be connected to the battery to charge
it.
Paul A. Smith,
Engadine, NSW.
Response: we’re sorry that you received apparently blank
chips and we are quite surprised by this. We did check the
programmed chips we have remaining in stock for that
project and they are all correctly programmed.
However, they were probably programmed at a different time from the ones we sent you. We will refund what
you paid for the chips and software.
You are right that there is an error in the PCB design
regarding diode D4. We will publish an errata and design
a revised board which we will order when the existing
stock runs out.
It would be worthwhile cutting the track between the
anode of D4 and the adjacent 100kW resistor and soldering a short wire from there to the opposite end of that
resistor, so that it provides proper protection to the
circuit.
You are also correct about the circuit caption being
wrong. However, we don’t agree with your statement that
“The circuit also has a flaw in that if the battery voltage
falls below the supply dropout voltage of REG2 the charger
will never be connected to the battery to charge it.”
If the battery drops below 12V, the output of REG2 will
simply be the battery voltage minus REG2’s dropout voltage, which is a fraction of a volt.
The relay will still operate down to below 9V. If your
battery is discharged down to below 9V, it would be advisable to slowly bring the battery up in voltage with a low
current charge rather than the high current available via
the charger controller.
Besides, a lead-acid battery that has been discharged to
9V will normally have severely reduced capacity due to
sulfation and will probably require replacement.
Celebrating 30 Years
siliconchip.com.au
Sophisticated radio design desired
I read the letter titled “Modern hifi AM radio receiver design desired” on pages 99-100 of the October issue, in the Ask Silicon Chip section. I too have
thought about building the February-April 1991 AM
Tuner design myself but realised most of the parts are
no longer available.
I have made enough simple AM and FM radio projects that I would like to build something more sophisticated. I would prefer a design which included
not just AM and FM but also LW and SW which are
still used in Europe.
Silicon Labs have the “SiXXXX” range of radio
chips that could be used. I noticed that one of the sets
includes DAB radio as well. I know you had a FM/
DAB radio project a while back but that was based on
a ready-made module.
Jeff Dunn,
Auckland, New Zealand.
Response: we will consider a radio design based
on the Si4685 IC but such a project would require
extensive software development and could take many
months to produce.
We also wonder whether it would end up being more
expensive to build than an equivalent commercial
product, such as the Jaycar AR1946 receiver which
has all the features you’ve asked for.
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Another request for a comprehensive radio design
I would like to see you design a multi-band AM/
FM radio using an Si4735 IC. The radio could receive
LW, MW, SW and FM (depending which IC version is
chosen). Tuning would be simple using two up/down
buttons plus one band change button. Stereo on FM
would be nice.
The advantage of this IC is than no alignment is
needed. The audio amplifier could be Class-D and
capable of around 10W/channel.
You could use a pre-built module. These are so
cheap, you could not buy a volume control pot for
the cost of the amplifier module.
Maybe for a future radio, DAB+ could be added
and the ability to play MP3 or WAV files when radio
reception (or programming) is poor. It could run from
three 18650 batteries (with its own internal charger).
These days, I find it hard to keep up with newer
technologies, I don’t know how you do it.
Rod Humphris,
Ferntree Gully, Vic.
Comment: as per the response above, if we did this,
we would use the Si4685 in order to have DAB+ reception in addition to FM, AM, SW and LW.
We wonder how many people will build the radio
given that the chips are only available in leadless
SMD packages.
These certainly can be hand-soldered but some care
is required. 18650 cells are problematic (there are a
lot of dodgy ones around); perhaps a LiPo pack would
be a better solution.
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Celebrating 30 Years
December 2017 13
Rail Guns – the stuff of science fiction writers for more than a century
(Jules Verne, for example) – are rapidly becoming the stuff of science fact!
Whether catapaulting aircraft off the deck of a carrier without
steam, propelling a projectile with such force that it does huge
damage without any explosive warhead . . . or even
launching satellites without rockets (still in the
future – or is it?), electromagnetic force
is changing conventional
wisdom even as we speak!
Rail Guns and
Electromagnetic Launchers
By Dr David Maddison
T
here is a surprisingly long history behind electromagnetic launchers, going back to the mid-19th century. In 1844, a Mr Benningfield (first name unknown)
invented an electric gun called the SIVA or Destroyer but
little is known of what became of it as there was no further
mention of it after 1844.
An advertisement for a demonstration of the device said
“Officers consider that this invention will, in great measure,
supersede Gunpowder, and say that it is very much more
to be feared than any Engine of War in use.
The balls were projected in a continuous stream at a
rate of more than 2,000 per minute, each ball having force
14
Silicon Chip
enough to kill at a greater distance than a mile with certain aim, and continue from year to year at a cost far less
than gunpowder, although with more force.”.
In 1845, in The American Journal of Science and Arts,
October edition (page 132), Charles G. Page described a
“magnetic gun” in which “Four or more helices arranged
successively, constitute the barrel of the gun, which is
mounted with a stock and breech. The bar slides freely
through the helices, and by means of a wire attached at the
end towards the breech of the gun, it makes and breaks the
connexion with the several helices in succession, and acquires such velocity from the action of the four helices as
Celebrating 30 Years
siliconchip.com.au
Benningfield’s
electric gun from
an advertisement
of 1844. Although
little is known of
it, the claims made
certainly seem
ambitious.
to be projected to the distance of forty or fifty feet.”
In 1901, Norwegian Kristian Birkeland is credited with
having invented the coil gun. A magnetised iron projectile was pulled through a series of solenoids, with a system to disengage power to the coils as the projectile passed
through them.
A later version used a coil instead of an iron projectile
and a novel method of switching in which the inductance
of the projectile coil was matched to the drive coils so that
the back-EMF of the drive coil matched the voltage of the
projectile coil so that switching would occur at zero current.
However, there seems to be a similarity with this invention and the 1845 one mentioned above.
The results were disappointing though, as a velocity of
only 100 metres per second was reached with a 10kg projectile fired from a 4m long cannon; much less than the
predicted 600 metres per second. Nevertheless, a projectile range of 1km was achieved. A major problem was be-
At left is the drawing
from Kristian Birkeland’s
1904 US patent entitled
“Electromagnetic gun”.
Figure 1 shows the cross
section of the barrel
illustrated in an unusual
downward pointing
orientation and the coils
in cross section. Note
the projectile contained
within the barrel. Full
patent document at siliconchip.com.au/link/aag6
Below is Birkeland’s
Electromagnetic (Coil)
Gun.
siliconchip.com.au
From the Earth to the Moon, an
1865 novel by Jules Verne,
tells the story of the Baltimore
Gun Club (a society of weapons
enthusiasts) and their attempts
to build an enormous ‘‘space
gun’’ to launch three people
in a projectile with the goal of
landing on the moon. Given the
date and the
lack of scientific
knowledge, some
of Jules Verne’s
assumptions
and calculations
are surprisingly
close to reality.
ing able to supply enough power to the device.
The above mentioned devices were based on solenoids
but the rail gun we know today was invented by Frenchman Louis Octave Fauchon-Villeplee in 1916 who called
it an electric cannon. Its power source was batteries.
His initial working model had a two-metre-long barrel
and was intended to accelerate a 50g, 270mm projectile
to 200 metres per second, for which a required current of
5000A at 40-50V was calculated.
In experiments a current of 600A was achieved which
could drive a projectile through 80mm of wood at 25m, the
limitation apparently being generating the large currents
required. The work was abandoned after World War 1.
In 1920, Fauchon-Villeplee described a rail gun designed
to propel a 100kg projectile at a muzzle velocity of 1600
metres per second, over a distance of 120km. The instantaneous power developed in the barrel would be 3.4GW at
an average current of 3.55 million amps.
The gun assembly with generators was to be mounted on
railway bogies and would have weighed 1000 tonnes. The
power was to be produced by a homopolar generator and
was designed to fire one shot every 20 minutes, consuming
60kg of petrol. The gun was not built due to lack of funding.
The June 1932 issue of “Modern Mechanics and Inventions” magazine mentioned two scientists whose work in
generating pulsed ultra-strong magnetic fields was seen as
the basis of an “electric cannon”.
One was P.L. Kapitza (a Nobel Prize winner) of Cavendish Laboratory, Cambridge University and the other was
T.F. Wall. It is not known where this work went in respect
of a gun but a dramatic image of the hypothesised gun was
produced for the magazine.
In 1933, a Texan by the name of Virgil Rigsby invented a
coil gun intended to be used as a “silent machine gun” but
the military had no interest in it. It was patented in 1934.
The first plans to actually use a rail gun for military service came from Joachim Hänsler in 1944, from Germany’s
Ordnance Office. Theory was developed and a device was
built using batteries as the power source but it was never
employed.
The device was able to propel a 10g mass to 1000 metres
per second. This was a good speed but not much better than
could be developed with chemical propellants at the time.
Further rail gun developments came from General
Electric in the USA, accelerating a 45g projectile to 550
metres per second in 1957; R.L. Chapman, D.E. Harms
Celebrating 30 Years
December 2017 15
Virgil Rigsby with what we would know as a coil gun today.
It used 17 coils and a timing mechanism, similar to that used
on car ignition systems at the time, was used to sequentially
activate the coils. This picture is from November 1936
Popular Science, but there was also an earlier version that
appeared in the June 1933 Popular Mechanics.
“Modern Mechanics and Inventions”
magazine from June 1932 showing a
proposed “electric cannon”.
and G.P. Sorenson accelerating 210mg to 9.5km/s in 1963
and D.E. Brast and D.R. Sawle accelerating 30mg to 6km/s
(21,600km/h!) in 1964.
The Australian contribution
In 1970, J.S. Adams, at what was then the Defence Standards Laboratory in Melbourne, accelerated a 300mg projectile to 3km/s.
The first large-scale rail gun in the world was built by
John P. Barber at the Australian National University in the
early 1970s and one experiment accelerated a 3g projectile
to 5.9 km/s. Its power source was a homopolar generator
facility designed by Sir Mark Oliphant.
The homopolar generator (see box) could deliver 500MJ
of energy with current pulses of up to 1.6 million amps. A
variety of rail guns were built with bore sizes from a few
millimetres to 20mm, with lengths from under a metre to
several metres and input currents of up to 400,000A.
The success of the Australian work led other major organisations around the world such as the US Defense Advanced Projects Agency (DARPA) to establish advanced
rail gun research programs in the latter half of the 1970s.
Another Australian rail gun was at what was then known
as the Materials Research Laboratory of the Department of
Defence at Maribyrnong in Victoria (an institution where
the Author used to work). The research program was general in scope and was about studying the science of these
devices with launch velocities up to 10km/s and input energies of up to 500kJ or more.
Unfortunately, the rail gun seems to be another area in
which Australia was once a world leader in a technology
that was not pursued.
Advantages and disadvantages of
electromagnetic launchers
Rail guns and coil guns have the advantage of greater
What is a homopolar generator?
A homopolar generator is a now uncommon type of DC electrical generator which
uses a rotating disc in a perpendicular magnet field to generate a potential difference
between the centre of the disc and its rim.
The homopolar generator used at ANU to
power the railgun had the disc in the form
of a heavy flywheel that could store enormous amounts of energy which could be
quickly discharged in the form of a current
pulse into the railgun or other experiments
it was connected to.
For details of the homopolar generator
used in ANU, readers are referred to “The Big
Machine” at siliconchip.com.au/link/aag7
The generator was in use from 1962 until 1985 after which it was dismantled. This
author is privileged to have seen this device.
Image credit: Australian National University: University Photographs, ANUA 226-895-2
16
Silicon Chip
Celebrating 30 Years
Mark Oliphant (in lab coat) demonstrates
the homopolar generator to the GovernorGeneral, Sir William Slim, October 1954.
siliconchip.com.au
Just what is a Rail Gun?
A rail gun comprises two parallel electrically conductive rails
bridged by a conductor connected together by a moveable armature. A DC current is applied to the rails and flows through the
armature and the resulting magnetic field causes acceleration of
the armature, which is also either the projectile or pushes on one,
down the rail and out of the device.
Often the armature has to be given a start by compressed gas,
for example, as if the current is applied when it is stationary it
might become welded to the rails. A plasma, which is electrically
conductive, can also be used as the armature in some implementations of the rail gun.
The Lorenz force drives the armature along the rails. In any inductive loop, which is essentially what the rails and armature are,
the Lorenz force acts to push the components apart via opposing
magnetic fields. If one part of the inductor is free to move, in this
case the armature, it will be driven along the rails in a direction determined by the polarity of the power. If the current is high enough
with a fast enough rise time, it can be ejected at great velocity.
The US Navy has advanced rail guns under development although deployment seems to be considerably delayed. Two contractors are involved in development, BAE Systems and General
Atomics Electromagnetic Systems (GA-EMS). The Navy’s short
term goal is a weapon in the 20MJ to 32MJ range that can shoot
a projectile 50 to 100 nautical miles with a repetition rate of at
least ten rounds per minute.
The amount of energy represented by 32MJ is the same as
4.8kg of C4 military explosive. It is also about the amount of energy behind a 10.5kg projectile with a velocity of Mach 7 (8644
km/h) although much less than that, maybe 50%, will be delivered to the target. By way of comparison, a tank’s 120mm gun
can generate 9MJ of energy at the muzzle and a cruise missile
like the Tomahawk can deliver 3000MJ of destructive power to a
target from 450kg of explosive.
While some weapons might be more destructive with the
amount of energy delivered to a target, rail gun projectiles are
Driving
Current
Magnetic
Field
Projectile
(Above): railgun
schematic showing
how opposing
magnetic forces are
established when a
current flows, forcing
out the projectile.
You can demonstrate
this effect at home
as explained in the
link in the text box.
(Right): simulation of
magnetic field lines in
a railgun at a certain
instant in time with
the electrical potential
on the rails shown
as different colours.
siliconchip.com.au
very fast in comparison to conventional weapons, are cheaper and
can be launched in greater numbers with a fully developed operational system.
An important consideration limiting the employment of shipmounted rail guns is the amount of electrical power required. The
Zumwalt-class destroyers of the US Navy are the only non-nuclear
vessels that have sufficient spare power available for a rail gun. A rail
gun capable of propelling a projectile to the desired range would required 25MW of available power to charge a capacitor bank or other
pulsed power system. The Zumwalt destroyer can produce 78MW
while a typical naval vessel only has 9MW spare. Existing vessels
would have to be fitted with extra power systems if rail guns were
to be retro-fitted.
GA-EMS has three rail guns under development. The 3MJ Blitzer,
the 10MJ medium range multi-mission rail gun system and the 32MJ
Advanced Containment system. A live action video of the Blitzer rail
gun in operation can be seen at “Blitzer AUSA 2016 ” siliconchip.
com.au/link/aah3
In August this year (2017) it was announced that GA-EMS had
completed final assembly and factory acceptance testing of a 10MJ
(megajoule) medium range multi-mission rail gun system in preparation for transport to a proving ground in Utah. This weapon is a
third generation design with a fifth generation pulsed power system.
It is designed for a fairly small footprint on ship and mobile platforms. The system was previously tested with projectiles accelerated
at 30,000g and the projectiles had two-way communication with the
ground station. In the current phase of development of this rail gun
there is a focus on the gun’s fire repetition rate.
Another version of the rail gun is one in which a plasma (hot electrically conductive gas stripped of its outer electrons) is fired rather
than a solid projectile. HyperV Technologies Corp. has developed
some of these devices. The plasma rail gun is not designed to operate in air but in a vacuum or near vacuum. It is intended to be used
in various types of nuclear fusion reactor projects, laboratory astrophysics experiments and in thrusters for spacecraft.
Projectile
Current
Force
Rail
BAE Systems prototype railgun on display on the USS Millinocket.
A GA-EMS railgun was on display at the same time. Note these were
on static display only and not installed on the ship and no testing has
yet been done at sea, though it had been planned to do so by now.
BAE Systems 32 MJ railgun
at the Naval Surface Warfare
Center in Dahlgren, Virginia,
USA. You can watch it in
action at “Electromagnetic
Railgun - First shot at
Dahlgren’s new Terminal
Range” siliconchip.com.au/
link/aah4
Celebrating 30 Years
December 2017 17
A concept from General Atomics about how a railgun might be used as a battlefield weapon. In direct fire mode a
projectile can reach the horizon in six seconds, in indirect fire mode the projectile is launched into space and can reach a
land target 370km away in six minutes.
safety for their users, since no potentially hazardous propellants and explosives are needed, which simplifies the
supply chain and strict storage and handling requirements.
Much higher projectile velocities can also be achieved compared with conventional guns. This leads to great destructive power by kinetic energy alone although some proposed
projectile designs have terminal guidance and even small
explosive charges.
Another advantage of rail guns in military applications
is the relatively low cost of the projectiles compared with
a guided missile.
But a significant disadvantage of all launcher designs
is the requirement for large generators and pulsed power
supplies.
The mass driver can theoretically achieve high enough
velocities for launching materials from Earth to space or
from objects in space where electricity may be the only
power source, eg, from solar panels and where no chemical fuels are available.
Note that by using chemical propellant guns of a very
special design it is also possible to launch materials into
space from Earth.
Google “Project HARP”, which stands for Super High
Altitude Research Project, [siliconchip.com.au/link/aah6].
By the way, this is quite different to, and should not be
confused with, the now-defunct HAARP project (HAARP:
Researching The Ionosphere), featured in a 2012 SILICON
CHIP article (siliconchip.com.au/Article/492). Also see the
Jules Verne Launcher [siliconchip.com.au/link/aah5].
18
Silicon Chip
The coil gun
A coil gun, also known as a Gauss rifle, uses one or more
coils mounted on a common axis to accelerate a projectile
down the central axis of the coil assembly. It is important
that when multiple coils are used that there is a proper
sequential activation and deactivation of adjacent coils or
the projectile will become trapped.
If one coil is used the projectile must be inserted at the
proper location within the coil body. (Imagine a magnetic
object put into the central axis of an electrically-energised
coil, it would simply oscillate back and forth under normal circumstances.)
A rail gun requires a projectile or armature to be in contact with rails but in a coil gun the projectile does not nec-
Representation of a coil gun. The projectile has passed
through the first set of coils which have been deactivated
and is being pulled and accelerated toward the middle
coil which has been activated. Having passed through the
middle coil, which will then be deactivated, the third coil
will be activated and the projectile accelerated toward that.
Diagram source: ZeroOne.
Celebrating 30 Years
siliconchip.com.au
A General Atomics Electromagnetic Systems 32MJ Advanced Containment railgun system in test configuration.
essarily need rails and can be suspended by the magnetic
field, although in some designs the coils runs along a track.
Coil guns are much more simple to construct than rail
guns due to fewer practical difficulties and are a popular
choice among hobbyists. Some links are provided elsewhere on hobby projects.
In 1978 a Soviet scientist by the name of V.N. Bondaletov,
using a coil gun, achieved a record for acceleration by accelerating a 2-gram ring to 5km/s over a distance of just 1cm.
Applications suggested for coil guns including firing projectiles into space, military mortars (one project that was
funded by DARPA has projected mortars twice the range of
conventional ones) and Electromagnetic Missile Launcher
(EMML) for launching Tomahawk cruise missiles. These
projects do not currently appear to be under active development. The Chinese are said to be developing an active
protection system for tanks based on a coil gun.
The mass driver for space launch
Electromagnetic launch systems have been proposed
as a cheaper method of getting materiel into space since in a conventional
rocket launch most of the mass of the Flight Body
launch vehicle is the rocket body with
relatively little payload. An electromagnetic launcher leaves the launcher device on the ground ensuring that
most of the flight body is payload.
Electromagnetic launchers have
been proposed to launch materials
A concept for an electromagnetic
launcher to launch payloads into
space from the side of a mountain.
Image source, Ian R. McNab, 2003.
siliconchip.com.au
from the Earth, Moon and other bodies such as asteroids.
In the case of a launch from Earth there is a significant
problem of high velocities required to launch objects into
orbit of greater than 7500 metres per second. This means
long launch tubes, high energies, high acceleration of 1000G
or more and aerodynamic heating of the flight body.
The high acceleration means that only robust payloads
such as water, solid metals, fuels and other items that can
easily sustain a high acceleration without damage can
be utilised. Certainly, humans are out of the question for
launch by this method.
The high velocity also requires some sort of cooling system and heat shield attached to the flight body.
For launches from the Moon and asteroids of mined raw
or refined materials the low gravity and lack of an atmosphere means that lower accelerations can be used and aerodynamic heating of the flight body is not an issue.
There have been several concepts of using a mass driver
for space launch.
Mass Driver 1 was an early constructed prototype mass
Evacuated Launch Tube
Containing
Railgun Accelerator
~10MWe power plant
to provide launch
power
High (2-3km)
mountain on or
near the Equator
Celebrating 30 Years
December 2017 19
ACCELERATION
TUBE
LAUNCH
EGRESS
TUBE
HATCH
PLASMA
EMPTY SLED
WINDOW
PROJECTILE
Y-AXIS
Z-AXIS
(VERTICAL)
X-AXIS
PROJECTILE
MAGLEV SLED
Launch ring concept. This has an underground accelerator
ring and an above ground launch ramp.
driver designed to launch materials from the lunar surface
to the fifth Lagrange point. This is an area of stable orbit
between the Earth and moon where it has been proposed
to build space colonies and where objects will remain in
place without station keeping.
The device was built by students at the Massachusetts
Institute of Technology in 1976/77 for around $2000. It had
20 drive coils, a “bucket” (armature) in which the payload
was contained and four copper tubes through which the
drive current, supplied by car batteries, was carried.
The bucket was electrically connected by brushes to the
rails and a microswitch was activated as the bucket passed
each coil causing the energising of the appropriate coils
in sequence via capacitor discharges which propelled the
bucket via the Lorenz force. An acceleration of up to 33g
could be achieved.
There is also a 2006 concept from LaunchPoint Technologies who developed the Launch Ring concept. This design
comprises a circular evacuated ring with a linear motor and
a sled containing the launch vehicle held without contact
with the ring by magnetic levitation. This is accelerated
around the ring multiple times until it has reached a velocity of 9000 metres per second at which point it is diverted
to a ramp built up a hill or mountain which is located at a
tangent to the acceleration ring.
It was estimated that the launch vehicle would reach the
required velocity in about one hour. Multiple sleds could
be maintained within the ring allowing multiple launches in sequence. The egress window would have a plasma
window at the exit point to prevent air entering into the
evacuated system.
Conceptual designs were created for both superconducting and non-superconducting systems. A later more cost
effective concept was also developed but details have not
been released. See siliconchip.com.au/link/aah7
LaunchPoint Technologies Launch Ring. The launch
tube would be built up the side of a mountain while the
acceleration tube would be buried in the ground.
higher maintenance and shorter service life; the inability
to launch light aircraft such as drones and a high thermal
signature and energy requirement due to the large amount
of steam that has to be produced for a single launch – a
typical figure is about 600kg. These systems are also very
heavy and take a lot of space in the ship.
EMALS uses a linear induction motor to propel a carriage
attached to the aircraft along the launch track.
Linear induction motors are also typically used on magnetic levitation trains and also the tracked train servicing
the terminals at the JFK Airport in New York and are a
well-established technology.
EMALS consists of six main systems comprising:
• Prime Power Interface that connects the ship’s power
to the energy storage generators;
• Launch Motor in the form of a linear induction motor;
• Launch Control System to control the current to the
Launch Motor in real time;
EMALS
(ElectroMagnetic Aircraft Launch System)
Traditionally, aircraft are launched from aircraft carriers
using a steam catapult. These are effective and reliable but
have a number of disadvantages, including uneven acceleration leading to excessive forces on air-frames and therefore
20
Silicon Chip
EMALS launch motor in land-based experimental
installation. Image credit: General Atomics.
Celebrating 30 Years
siliconchip.com.au
“Below deck” view of EMALS equipment.
Image credit: General Atomics.
EMALS energy storage system in land-based testing.
Image credit: General Atomics.
• Energy Storage System that provides power to the Launch
Motor for two to three seconds during the launch process and is recharged between launches;
• Power Conversion System that is a solid state system
that converts power from the Energy Storage system to
the appropriate voltage and current to drive the shuttle
along the Launch Motor and
• Energy Distribution System that delivers power from
the Power Conversion System to the launch motor via a
system of cables and connectors.
Like other linear induction motors, EMALS use a row
of stator coils along the track. These are energised only in
the vicinity of the shuttle as it is propelled down the track
to minimise losses. EMALS can launch a 45,000kg aircraft
91m down the length of the track to achieve a launch velocity of 240km/h.
A key to the operation of EMALS is an energy storage
mechanism. Ship power is used to spin up a series of four
disk (flywheel) alternators which are discharged during
the launch process. A maximum energy launch will reduce the speed of the rotors from 6400 RPM to 5205 RPM.
It takes 45 seconds to recharge which is faster than a
steam catapult can recharge. The maximum energy launch
represents 136kWh of energy or about the same as four litres of petrol.
EMALS offers lower maintenance and staff requirements,
lower life-cycle cost, reduced thermal signature, increased
capabilities to launch lighter unmanned aircraft and future heavier aircraft and with reduced weight and volume.
EMALS also offers flexibility of installation so can also be
used on a variety of ship sizes.
The United States Navy has an EMALS system operational on the USS Gerald R. Ford (CVN 78) and will next
have one operational on the USS John F. Kennedy (CVN 79).
Associated with EMALS but a separate system is the
Advanced Arresting Gear (AAG) system. This system has
only just finished development after many delays but is
currently installed on the USS Gerald R. Ford and will
When is a “Rail Gun” not a “Rail Gun ”
There are various devices which have been called “Rail Guns”
over the years which have nothing to do with the electromagnetic
devices we are talking about here. We show two of these below.
There are the railway-mounted heavy artillery pieces of both
world wars. The 800mm German Schwerer Gustav (WWII) is the
largest gun ever made and used in combat, and could fire seven
tonne shells a distance of 47km.
Another type of “rail gun” which you may encounter uses custom-made rifles (using conventional ammunition), designed for
competitive shooting where the emphasis is on ultra-high precision. See siliconchip.com.au/link/aah8
Built in 1941, Germany’s Schwerer Gustav (English:
Heavy Gustaf) rail-mounted monster. See siliconchip.
com.au/link/aah9
Unlimited class railgun for competitive shooting – not
to be confused with the electromagnetic variety. Image
source: siliconchip.com.au/link/aaha
siliconchip.com.au
Celebrating 30 Years
December 2017 21
Resources
“The Big Machine” article about the homopolar generator
built by Sir Mark Oliphant at the Australian National University
which was used to power the world’s first large scale rail gun:
siliconchip.com.au/link/aahb
A very nice and clear explanation of the physics of a moving bar
in a magnetic field which is relevant to the rail gun can be seen
at “Electromagnetic Induction: Induced EMF in a Moving Bar in
a Magnetic Field” siliconchip.com.au/link/aahc
Another video explaining the physics is “Rail Gun example”
siliconchip.com.au/link/aahd
and “U.S. Military’s Most Powerful Cannon - Electromagnetic rail
gun - Shoots 100 miles - Mach 7” siliconchip.com.au/link/aahe
Advanced Arresting Gear, below deck view
be installed in other carriers of that class such as the USS
John F. Kennedy. Energy is absorbed via water turbines
and induction motors.
Videos to watch:
“Fighter Lands on Next Generation Carrier USS Gerald R. Ford for the First Time” siliconchip.com.au/link/aahg
and “USNI News Video: Sailors Describe First Fighter
Landing, Launch on USS Gerald R. Ford” siliconchip.com.
au/link/aahf
The US Department of Defense has also given the Indian
Navy approval to purchase EMALS and AAG.
Acknowledgement: The author wishes to acknowledge the assistance of Andrew Krelle in locating some of the source documents.
The rail gun in the Australian Parliament
Rail guns have been mentioned nine times in the Federal Parliament from 1984 to 1988.
This was mainly in connection to the one that was under development by the then Defence Science and Technology Organisation’s Materials Research Laboratory in
Maribyrnong, Victoria and in relation to the then Government’s opposition to the Strategic Defense Initiative
of the United States (see below).
The questions can be seen here: siliconchip.com.au/
link/aahi
Geoff Pryor’s 1984 cartoon about then Prime Minister Bob Hawke’s embarrassment when it was disclosed that he
had committed Australia to collaboration on the US “Star Wars” program (Strategic Defense Initiative) through the
Australian Department of Defence despite his party’s opposition to it. siliconchip.com.au/link/aahh
22
Silicon Chip
Celebrating 30 Years
siliconchip.com.au
Building your own electromagnetic launcher device – some ideas
Building some type of electromagnetic launcher is within the
scope of an experienced and responsible electronics hobbyist
and there are many plans and videos on the Internet showing
how to do this.
SILICON CHIP presents these URLs for information only. We cannot advise you on the legality of making a high power one in your
jurisdiction, particularly in Australia with its many “nanny state”
laws so you would need to determine this yourself.
One tip: never refer to it as a ‘‘gun’’– rail or otherwise!
Nevertheless, here are a few examples from overseas enthusiasts. While they do not have anything like the energy of a traditional firearm, very high energies and voltages are involved in
devices of this kind and they can be potentially lethal.
A video safely demonstrating the principles of a rail gun using
only cardboard, aluminium foil, glue, 9V battery, a piece of steel
rod and two magnets followed by instructions on how to build a
small rail gun can be viewed at “How To Build a Railgun Experiment” siliconchip.com.au/link/aahj
The author has additional details and other interesting projects
at siliconchip.com.au/link/aahk
Very simple experiment
to demonstrate railgun
principles using basic
materials of cardboard,
aluminium foil, glue, 9V
battery, a piece of round metal steel rod and two magnets.
The magnets may not be needed if a high enough current
is used.
A variation of this idea is to use model railway track as the two
parallel rails as shown in the video “Lorentz Force Experiment using N-Scale Track (240fps)” siliconchip.com.au/link/aahl and a
similar experiment without rail track “Fuerzas de Lorentz (corto) /
Lorentz forces (short)” siliconchip.com.au/link/aahm
David Wirth
and his
portable
railgun.
It uses 3D
printed
components
and is
controlled
by an
Arduino.
You can
read more at siliconchip.com.au/link/aahn
A DIY rail gun by Zebralemur siliconchip.com.au/link/aahq is
claimed to be the most powerful built by an individual. It uses 56
400v, 6000µF capacitors.
Zebralemur’s home made railgun, claimed to be the most
powerful built by a non-government entity.
An Instructable on building your own rail gun is at siliconchip.
com.au/link/aahr This person makes a coil gun and provides an extensive discussion about the electronics involved.
“World Fastest Six Stage Coil Gun Yak Questions Answered”
siliconchip.com.au/link/aahs
Thinkbotics, a company that supplies to robot experimenters
have developed the EM-15 coil gun and their website siliconchip.
com.au/link/aaht states that plans will be available ‘‘soon’’.
The electronics of the coil gun consist of a voltage step-up transformer converter, a Cockcroft-Walton voltage multiplier cascade,
a capacitor energy storage bank, a voltage comparator to set the
charge voltage on the capacitor bank, an SCR switching section
and a single accelerator coil.
Construction details were published in the March 2008 edition
of Nuts and Volts magazine, see siliconchip.com.au/link/aahu
Here is a video of a home made coil gun siliconchip.com.au/
link/aaho You can read more about this project at siliconchip.
com.au/link/aahp
Thinkbotics EM-15 coil gun.
The CG-42 coil
gun. Note the eight coils
which are sequentially
energised to propel the
projectile through.
siliconchip.com.au
A simple mass driver can be built with plans at this link and
there is also a video of the device. siliconchip.com.au/link/aahv
Finally, here’s a clever launcher contraption made with rare earth
magnets, no power required. “Magnet Gun -magnetic launcher”
siliconchip.com.au/link/aahw
Celebrating 30 Years
SC
December 2017 23
by Jim Rowe
(no, that’s not
him flying . . .)
Build this
Touchscreen
Altimeter
for hang-gliders, etc
With full WEATHER REPORTING on board!
This accurate altimeter has a bright colour touchscreen to display altitude
in feet or metres, atmospheric pressure, temperature and relative humidity.
It can show all readings at once or provide a larger display for altitude –
the most important one if you’re flying!
I
t’s especially useful for hanggliders, where the touchscreen facility is most useful.
Some ultralights, too, have a dearth
of cockpit instruments – just take this
one along with you when you fly! And
you can use a solar panel to keep the
battery charged on long flights.
Our first altimeter was featured back
in 1991 and since then sensor technology has changed radically and become
much, much cheaper.
Apart from being based on our
popular Micromite Touchscreen, our
Touchscreen Altimeter uses two tiny
electronic modules which have been
recently reviewed in SILICON CHIP: the
Elecrow GY-68 digital barometer mod24
Silicon Chip
ule (it’s elsewhere in this issue) and the
AM2302/DHT22 temperature and humidity module (February 2017).
Of course, even if you have no intention of leaving the Earth’s surface,
this project will also provide a useful
weather station display with the advantage of Touchscreen control.
And if you ever decide to climb Mt
Everest, this little unit can even cater
for that extreme: the summit of Mt Everest is reckoned at 8848m above sea
level (we go up to 9000m!) and our
temperature goes all the way down to
-40°C (Everest seldom goes this low
during the climbing season).
Battery charge may be slightly problematical – best take a solar charger
Celebrating 30 Years
panel with you!
By the way, we are well aware that
you can purchase various weather stations with colour displays very cheaply. But they don’t have the touchscreen
facility nor the ability to simply highlight one reading, such as temperature.
Presentation
The Altimeter is housed in two small
plastic cases, one for the Touchscreen
Micromite BackPack and the other for
the two sensor modules. The larger
UB3 case is 130 x 68 x 43mm (LxWxH)
and houses the Touchscreen Micromite
BackPack, together with the single
18650 lithium-ion cell which powers
the project and the Elecrow charger/
siliconchip.com.au
Specifications
Altitude range:............................................ 0-9000m (0-29520ft) above MSL or GND, with 1m resolution and ±1m accuracy
Temperature range: ................................... -40°C to +80°C, with 0.1°C resolution and ±0.5°C accuracy
Relative Humidity measuring range:......... 0 to 100%, with 1% resolution and ±2% accuracy
Barometric Air Pressure range: .................. 300-1100hPa (mBar), with 0.1hPa resolution and ±0.12hPa accuracy*
*between 950 and 1050hPa, at 25°C
Power requirements: .................................230mA at 5V, (380mA at 3.7V from inbuilt 18650 Li-Ion cell)
upconverter module (reviewed in
SILICON CHIP, August 2017 – www.
siliconchip.com.au/Article/10754).
The smaller UB5 case measures 83
x 54 x 31mm (LxWxH) and houses the
two sensor modules. The two cases are
connected together via multi-way cable, which can be as short or as long as
needed to suit your purpose.
So why have two cases instead of
one?
We tried using a single larger case
but it had problems with internal heat
build-up which compromised the
reading accuracy. More on this anon.
Circuit details
Fig.1 shows how all the modules are
connected together.
Starting with the DHT22/AM2302
temperature and RH module, we won’t
go into its operation in great depth
here since we covered this in detail
in the February 2017 article (pages
46-48 – www.siliconchip.com.au/
Article/10529).
The main things to know are that it
has its own dedicated 8-bit microcon-
troller, to measure relative humidity
via a special polymer capacitor and
temperature via a negative temperature coefficient (NTC) thermistor.
Each time the micro uses these to
take a set of measurements, it calculates the corresponding temperature
and relative humidity (RH) and sends
them out as a serial 40-bit data package via the DATA line.
The data is encoded using a special
pulse-width-modulation system and
this is decoded by the Micromite and
displayed on the touchscreen.
Fig.1: the Altimeter is based on two low-cost modules, one measuring barometric pressure and the other temperature
and relative humidity. Their readings are monitored by a Touchscreen Micromite BackPack which displays the data
on a touchscreen readout. An 18650 cell supplies power, itself kept charged by a mini solar/USB charger.
siliconchip.com.au
Celebrating 30 Years
December 2017 25
Here’s the display in Altimeter mode.
The green text shows the altitude units
(metres or feet) and the reference level
(MSL or GND).
Barometric Pressure
and Altitude
Basically, atmospheric pressure
is due to the weight of air immediately above your location.
The primary SI unit for pressure
is the Pascal (Pa), which is equivalent to a force of 1 Newton per
square metre.
A column of air one square centimetre in cross section, measured
from sea level to the top of the
Earth’s atmosphere, has a mass
of about 1.03kg and a weight of
10.1325N.
This corresponds to a pressure
of 101,325Pa or 1013.25hPa (hectoPascals), since 1hPa = 100Pa. So
the ‘standard atmosphere’ is defined
as 1013.25hPa.
The actual barometric pressure
at any particular location depends
upon its elevation, or altitude, with
respect to mean sea level (MSL),
because the higher the elevation,
the lower the weight of air directly
above you and the lower the pressure.
It also depends on various aspects of the weather, including the
amount of moisture in the atmosphere – ie, the relative humidity
(RH).
The relationship between air
pressure and altitude is usually defined as the Barometric Formula.
This can be written as:
where altitude is in metres, P is the
measured air pressure and Po is the
air pressure at MSL, or 1013.25hPa.
If you substitute 1013.25 for P in the
above formula, the result will be 0
metres which is MSL.
26
Silicon Chip
When you touch the button at the
bottom of either of the other displays,
this ‘Change Settings’ display appears,
allowing you to make changes.
Here’s the display in Weather Station
mode. Again, you can touch the button
at the bottom to change any of the
settings or switch to Altimeter mode.
Every DHT22/AM2302 module is
calibrated during manufacture with its
calibration coefficients saved in its micro’s one-time programmable memory.
These coefficients are used to achieve
impressive levels of measurement resolution and accuracy.
The RH measurement range is from
0-100%, with rated resolution of 0.1%
and an accuracy of ±2%, while the
temperature measurement range is
from -40 to +80°C with a resolution
of 0.1°C and an accuracy of ±0.5°C.
The Elecrow GY-68 barometer-altimeter-temperature sensor module is
based on the BMP180 device made by
Bosch Sensortec, a division of the large
German firm Robert Bosch GmbH.
(www.boschsensortec.com)
The BMP180 is based on piezo-resistive MEMS technology, where MEMS
stands for ‘MicroElectroMechanical
Systems’. It uses a tiny sensor element
which flexes mechanically in response
to changes in atmospheric pressure,
with the flexing sensed by measuring
changes in the element’s resistance.
The BMP180 chip is fitted inside a
tiny 3.6 x 3.8 x 0.93mm metal package, which has a very small vent hole
(about 0.5mm diameter) in the top to
allow the sensor element access to the
outside air.
Apart from the sensor element, there
are three other functional blocks inside
the device: an ADC (analog to digital
converter) to make the measurements,
a control unit which also provides the
I2C serial interface for communicating
with an external micro, and finally an
EEPROM which has 22 bytes of storage
for the device’s 11 x 16-bit calibration
parameters.
As with the DHT22/AM2302, every
BMP180 device is individually calibrated during manufacture and the
calibration parameters are saved in
its EEPROM.
So the external micro can read these
parameters and use them to correct
that sensor’s readings for offset, temperature dependence and other factors.
With suitable software, the BMP180
can provide high accuracy measurements of barometric pressure, temperature and altitude above mean sea
level (MSL).
The quoted relative accuracy for atmospheric pressure is ±0.12hPa (hectoPascals) from 950-1050hPa at 25°C,
while the absolute accuracy is quoted
as -4/+2hPa over the range from 3001100hPa and for temperatures from
0-65°C.
All this comes from a chip which
only draws about 12µA from the +5V
supply!
Both sensing modules have the ability to measure air temperature. We’re
taking advantage of this in our Altimeter project, as the software for the Micromite takes the average of the two
temperatures to achieve optimum display accuracy.
Celebrating 30 Years
Lithium battery and charging
Since its main application is as an
altimeter for ultra-light aircraft and
hang gliders, we needed a battery power supply which was compact and light
in weight, with reasonable battery life.
With those factors in mind, we settled on a single 18650 lithium-ion cell
as the battery, together with one of the
Elecrow Mini Li-Ion Charger/Converter modules.
A quality 18650 cell like a Panasonic, Sanyo or similar will have an energy storage capacity of between 1500
and 3400mAh (milliamp-hours) when
fully charged.
So since the project draws about
230mA at 5V (mainly to power the
Micromite and its backlit LCD), which
translates into about 390mA drawn
siliconchip.com.au
Interior view of
the main unit,
housed in a
UB3 Jiffy box.
The Micromite
Backpack
fixes to the
box lid with a
cutout for its
touchscreen
display.
from the 3.7V Li-Ion cell (allowing for
converter efficiency), it should be capable of running the unit for between
three and eight hours.
Watch those 18650s!
As we pointed out in a recent article, there are 18650s . . . and
18650s. Don’t be tempted to
use a “bargain” or unknown
brand (did someone mention
ebay?), especially one labelled higher than 3400mAh
– they’re a con, as no such
18650 cell exists yet!
Similarly, any 18650 cell
you use should have protection circuitry built in – it
makes the cell slightly longer
but it means it won’t overcharge or overdischarge.
However, we’ve seen
cheap “protected” cells
which contain no more than
a spacer to make them look like
they’re protected.
Our tip is to always buy a reputable brand and preferably, buy here
in Australia. At least then you have
some recourse if the 18650 turns out
to be a dud.
Charging
The Elecrow Charger module allows
charging the 18650 Li-Ion cell from the
USB port of a PC or a low-cost USB
plugpack or alternatively, from a small
solar (photovoltaic) panel.
As well, it provides a DC-DC converter to boost the 3.7V terminal voltage of the Li-Ion cell to the 5V level
needed to run the Micromite BackPack and the two sensor modules.
This second function only comes
into operation when power switch
S1 is closed.
One minor shortcoming of Elecrow’s
Mini charger module is that it doesn’t
provide any ‘pass through’ of the USB
data lines between its USB input and
output connectors (CON2 and CON4).
But this only affects the initial uploading of the Weather Station/Altimeter
software into the Micromite – not normal operation.
Luckily, the initial software uploading to the Micromite can be easily
done, as shown in the circuit.
You will need to connect the 5V/TX/
RX/GND pins of the Micromite to one
of the USB ports of your PC via either
a Microbridge module or a standard
low cost CP2102-based USB/
UART bridge module.
If you’re using one of the newer V2
Micromites, it’s even easier since these
have a Microbridge built in. So all you
need to do for uploading the software
is connect the Micromite’s mini USB
connector directly to a USB port of
your PC or laptop.
Why two cases?
Now let’s turn to the physical side
of the project and explain why the
project is split into two small cases,
instead of a single case.
We started with everything squeezed
into a single UB3 case, the smallest
practicable size to fit everything in.
We soon discovered that the heat
Fig.2: this
wiring diagram
matches the
photo above
but the wiring
is slightly
clearer. Note
the reversed
colour coding
on the “Bat
Out” terminal
– black is
positive and
red is negative!
siliconchip.com.au
Celebrating 30 Years
December 2017 27
Weatherproofing
Because the sensor unit (especially)
would normally be used in the open air
(where it can read temperature and pressure) we would be inclined to weatherproof
it as much as possible, consistent with still
being able to make reliable readings.
To protect them, a conformal coating,
such as HK Wentworth’s “Electrolube HPA”,
could be sprayed on the underside of PCBs
and also on any soldered joints. Don’t spray
the top side of any of the modules!
Errata: there is a discrepancy
between the circuit diagram
(Fig.1) and wiring diagram (Fig.3)
Some DHT22/AM2303 modules come
attached to a small breakout board as
shown in El Cheapo Modules Part 4
(February 2017; www.siliconchip.com.
au/Article/10529).
If using the breakout board, the 1kW
resistor and 100nF capacitor shown in
Fig.1 are not needed and the DHT22 can
be wired to the DIN socket as shown in
Fig.3. Otherwise, if your module comes
with no breakout board, solder the resistor
and capacitor as shown in Fig.1.
from the Micromite and (mainly) its
LCD Touchscreen backlighting steadily raised the temperature inside the
case, so that the apparent air temperature rose significantly, giving spurious readings.
So that’s why we ended up with two
separate cases.
As shown in the photos, the two
sensor modules are mounted in the
bottom of the smaller case, which has
two 3mm diameter ventilation holes in
the bottom of the case to ensure that
conditions inside are substantially the
same as those outside.
Inside the main unit, the Micromite BackPack and its Touchscreen
are mounted under the case lid, while
the Elecrow Mini Charger module is
mounted on the bottom at the lefthand end.
The Li-Ion cell holder is mounted
on the front side of the case, as low as
possible so that it just clears the underside of the Micromite PCB when
the lid assembly is attached.
In order to do this, the Mini Charger
module is attached using only three
screws, and in addition part of the
cell holder’s ‘side flap’ is cut away at
the positive end.
Also mounted on the front side of
the case to the right of the Li-Ion cell
holder is power switch S1, a mini
SPDT toggle switch.
Construction
As shown in the layout/wiring diagram of Figs. 2 and 3, assembling
both units is pretty straightforward
because we are just linking up prebuilt modules.
But before you can begin the assembly, you’ll need to prepare both boxes
by drilling and cutting the
various holes. To do this,
follow the diagram of Fig.4
and 5 closely.
You can avoid cutting out
and drilling the holes in
the UB3 box lid/front panel if you buy one of the
laser-cut front panels
from the SILICON CHIP
online shop.
Another point to note is that before
fitting any of the components into the
larger UB3 case, you’ll need to cut
away four of the moulded splines inside the front side of the box, as shown
in Fig.4. This is to allow the 18650 LiIon cell holder to be attached to the inside, down low enough to clear both
the Mini Charger module and the underside of the Micromite LCD BackPack module.
The splines can be cut away with
a sharp hobby knife, or a small rotary
tool if you prefer. Once the two boxes
have been prepared you can fit the two
modules into the UB5 box. Here the
AM2302/DHT22 module is mounted
inside the box at lower right, using
three M2.5 x 8mm machine screws
and nuts, with three extra M3 hex nuts
used as spacers.
The GY-68 barometer module is
mounted in the same way at upper left,
in this case using a single M2.5 x 8mm
machine screw and nut, with a single
M3 nut again used as a spacer.
The cord grip gland can also be fitted
Fig.3: photography and wiring diagram for the sensor unit,
built into a UB5 Jiffy box. We originally built the whole
project in one box but found the heat from the Micromite
display compromised the accuracy of readings.
28
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Celebrating 30 Years
siliconchip.com.au
in the 12.5mm hole at the left-hand end
– but don’t tighten up the outer cord
gripping nut at this stage (only when
you have fed the cable through it).
Next cut off two sections of SIL header socket strip: one four clips long, and
the other three clips long. After removing any burrs these are slipped over the
4-pin header on the barometer module
and the 3-pin header on the AM2303
RH sensor module, ready for soldering the various wires from the connecting cable.
To prepare the cable itself, carefully
remove about 50mm of the outer plastic
sleeve from one end. Then peel back
the metal screening foil and twist it together with the bare wire just inside it.
Strip away about 4-5mm of insulation from the ends of the main conductors. After these ends are tinned, all of
the wires together with the screening
foil and wire can be passed through
the cable grip gland, until the end of
the cable’s outer sleeve is about 5mm
past the inner end of the gland. Then
the gland’s outer nut can be tightened
up to hold the cable in this position.
Then solder the various wires to their
correct pins of the header sockets on
the two modules. We suggest that you
use the colour coding shown in Fig.3,
to help avoid swapped connections.
Two small points to note: if the cable
supplied has six wires instead of five,
connect the ‘extra’ white wire to the
same socket lugs as the black ground
wire and the screening foil wire.
Also note that the red wire of the
cable must connect to the VIN socket
lug for the GY-68 module as well as
the VCC lug for the AM2302 module,
while the black wire must connect to
the GND lugs for both modules. This
will involve two short lengths (about
40mm) of insulated wire, ideally with
red and black insulation respectively.
The internal wiring of the UB5 sensor unit should now be complete and
you can fit the box lid. All that will
then remain is to fit the 5-pin DIN plug
to the other end of the cable.
To do this, first slip the plug’s outer
plastic sleeve over the end of the cable and out of the way. Then carefully
remove about 15mm of the cable’s outer sleeve from the end, and as before
peel back the screening foil and twist
it together with the bare earthing wire.
Then strip away about 5mm of the insulation from each of the inner wires.
Next, twist the ends of the black and
white wires together, and lightly tin
siliconchip.com.au
the ends of all bared wires before soldering them to the rear of each of the
plug’s pins.
As shown in Fig.3, the blue wire solders to pin 1, the green wire to pin 4,
the black/white/screen wires all to pin
2, the orange wire to pin 5 and the red
wire to pin 3.
When you’re happy with these connections, squeeze together the cable grip
lugs on the rear of the lower part of the
plug shell using a pair of pliers, so that
they will hold the cable in position.
Then fit the upper half of the shell
and slide the plug’s outer plastic
sleeve back up the cable and over
the plug’s metal shell, to hold it all
together.
Main unit assembly
Most of the information you’ll need
to assemble everything in the UB3 main
unit box can be found in the diagrams
of Fig.2, along with the internal photo.
The easiest way to do this is in the following order:
Main Unit and Sensor Unit Drilling Diagrams
Fig.4: the main unit
is built in the larger
(UB3) Jiffy box,
drilled and cut as
shown here. These
diagrams are
shown here close
to 2/3 life size (ie,
if photo-copying to
use as a template,
you’ll need to
enlarge them to
150%).
To save you some effort and at the same time achieve an even more
professional result, a laser-cut lid/front panel is available in clear or
black Acrylic from the SILICON CHIP Online Store: siliconchip.com.au/
Shop/19/3337 (clear) or siliconchip.com.au/Shop/19/3456 (black).
Fig.5 (left): the sensor
unit is built in a smaller
UB5 Jiffy box, drilled as
shown here.
Celebrating 30 Years
December 2017 29
Fig.6: a side-on
“X-ray” view of
the main unit
assembly. The label
is held in place by
the acrylic lid but
a very fine mist
of spray glue will
help to keep it in
intimate contact.
First, fit the 5-pin DIN socket to the right-hand end of the
box using a pair of 6mm long M2.5 screws and nuts. Then
mount power switch S1 in the 6mm hole in the front side of
the box, as shown in Fig.2. Next, mount the Elecrow Mini
Solar/LiPo Charger module in the bottom of the left-hand
end of the box, using three 9mm long M2.5 screws and nuts,
together with three M3 nuts as spacers. The module should
be mounted with the USB micro input socket end to the left,
just inside the stepped access hole.
Slide the Li-Ion cell holder down inside the front of the
box as far as it will go, orientated as shown in Fig.2. This
should allow you to mark the location of the two holes which
need to be drilled in the bottom of the holder, to match the
holes already drilled in the box. You should be able to mark
the hole locations using a small scriber or needle.
Then remove the cell holder again, so that you can easily drill a 2.5mm hole in each of the two marked positions.
After drilling remove any burrs with a larger drill or countersink, and if you can manage it also countersink both
holes on the inside of the holder. If you slide the prepared
holder back down into the box, you should then be able
to fasten it in position using two 6mm long countersinkhead M2.5 screws and nuts – with the nuts on the outside
as indicated in Fig.2.
When the holder is in place, you need to use a sharp knife
or rotary tool to cut away a section of the left-hand upper
‘wing’ of the holder, as indicated by the cross-hatched area
in Fig.2. This is to prevent it from interfering with some
solder joints on the underside of the Micromite BackPack
PCB, on the latter’s front left. You can also see this in the
internal photo.
Solder the ends of the Li-Ion cell holder’s leads to the
rear lugs of the JST2.0 socket on the Charger module, after cutting each one to an appropriate length and stripping
and tinning about 4mm from the end of each wire. The red
wire should be soldered to the lug marked ‘+’, and the black
wire to the lug marked ‘-’.
Next connect the two wires from the JST2.0 plug lead connected to the socket on the Charger module labelled ‘BAT
OUT’, to their designated locations. Note that since many
of these plug leads have reversed colour coding, the black
positive wire should be connected to the uppermost lug of
S1 while the red negative wire connects to pin 2 of CON1.
All that remains is to add the rest of the wiring, using
Fig.2 and the internal photo as a guide.
Note that the three wires from CON1 which are marked as
30
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connecting to pins 17, 18 and 21 of the Micromite should be
soldered at their upper ends to the lugs of a 3-way section
of SIL socket strip, while the wires marked +5V and GND
should be soldered to a 2-way section of the same socket
strip. Both sections of socket strip will then be ready to connect to the corresponding pins of the Micromite.
The next step is to mount the Micromite BackPack and its
LCD touchscreen to the underside of the box lid, or to the
replacement laser-cut acrylic lid/panel if you are using this.
Parts List – Touchscreen
Altimeter & Weather Station
1
1
1
1
1
1
1
1
1
UB3 jiffy box (130 x 68 x 44mm)
laser-cut Acrylic front panel to suit above #
front panel label to suit ^
UB5 jiffy box (83 x 54 x 31mm)
Micromite V2 LCD BackPack + 2.8-inch LCD #
Elecrow GY-68 barometer/altimeter module #
DHT22/AM2302 temperature/RH module #
Elecrow mini LiPo/Li-Ion charger module #
1kW resistor and 1 100nF ceramic capacitor if
not using a DHT22 with breakout board
1 18650 rechargeable Li-Ion cell
1 1 x 18650 Li-Ion cell holder
1 SPDT mini toggle switch
1 5-pin DIN socket, panel mounting
1 5-pin DIN plug, inline type
1 1.5m length of 5/6-way screened ‘computer’ cable
1 3-6.5mm cable gland
7 M2.5 x 8mm pan head machine screws & nuts
7 M3 hex nuts
2 M2.5 x 6mm pan head screws and nuts
5 M3 x 6mm pan head machine screws
1 16-way female header (to cut into 1 x 4-way,
2 x 3-way and 1 x 2-way)
4 M3 x 10mm long machine screws
4 M3 Nylon flat washers
4 12mm long M3 tapped Nylon spacers
2 M2.5 x 6mm countersink head screws and nuts
1 120mm length of rainbow ribbon cable (to
make interconnections)
# Available from the SILICON CHIP Online Shop:
siliconchip.com.au/Shop
^ Download from siliconchip.com.au/Shop/11/4482
Celebrating 30 Years
siliconchip.com.au
End-on views of the main
unit (left photo) showing
the connections for
power in, from either
a solar panel or a USB
supply/PC port; and
(right photo) the 5-pin
DIN socket which
connects to the
sensor unit.
Just before you do this, however, you
may want to attach the front panel artwork shown in Fig.7 to the lid/panel,
to make it look more professional.
For more information on assembling
and using the TouchScreen Micromite
BackPack, refer to the article in the
May 2017 issue (www.siliconchip.
com.au/Article/10652).
You can see how the BackPack and
LCD is attached to the rear of the lid/
front panel in Fig.6.
The LCD board is attached directly
to the panel using four 10mm long M3
machine screws, with 1mm thick Nylon flat washers as spacers and four
M3 x 12mm long tapped Nylon spacers
underneath as ‘long nuts’. Then the
Micromite BackPack PCB is attached
to the lower ends of the tapped Nylon
spacers, using only three 6mm long M3
machine screws.
No screw is used in the front left
position, because if fitted the head of
this screw would conflict with the top
of the Li-Ion cell holder during final
assembly.
Note that all connections between
the Micromite BackPack PCB and the
LCD board above it are made via a 14-
way SIL header and socket at their
right-hand ends.
Once the Micromite and LCD boards
are secured to the underside of the
front panel, you’re almost ready for
final assembly of the main unit.
Only two things remain to be done:
slipping the 18650 Li-Ion cell into its
holder (making sure that its positive
end is to the left) and then fitting the
3-way and 2-way SIL sockets on the
wires from the 5-way DIN socket to
the correct pins along the rear of the
Micromite PCB.
Plug the cable from the sensor unit
into CON1, so the two units are linked
together.
Programming the firmware
Your Altimeter is now virtually
complete but you need to download
the project’s firmware program from
the SILICON CHIP website, and then upload it to the Micromite.
The firmware for this project is
called “Altimeter.bas”, and you
can download it (free to subscribers)
from www.siliconchip.com.au
The three
mounting screws for the
Elecrow Charger PCB and the 5-pin
DIN socket on the end. The 18650 cell
holder mounts on the side wall of the case (see nuts).
siliconchip.com.au
Celebrating 30 Years
The next step is to connect the Micromite in your Altimeter/Weather
Station to a USB port of your PC, either
directly in the case of a Micromite V2
or via a USB/UART bridge module in
the case of a Micromite V1.
Either way, we suggest that you start
up Control Panel>Device Manager to
make sure that the Micromite has been
recognised as a virtual COM port and
to take note of the COM port number
and baud rate it has been allocated.
Now you should be able to start
up the MMEdit program and use it to
open the downloaded Altimeter.bas
program.
Then after making sure that MMEdit
can communicate with the Micromite
in the Altimeter/WeatherStation, it’s
just a matter of getting it to upload
the program and then set it running.
Since the programming connection
to the PC also provides power, you
should find that the Altimeter/WeatherStation springs to life as soon as the
program is set running.
You should see the display on the
LCD showing the altitude, air temperature, the relative humidity, the barometric air pressure (see photo of the
Weather Station display).
If all is well so far, the programming cable can be disconnected from
the Micromite.
The display will probably go dark
again, unless your have turned on
power switch S1 and your Li-Ion cell
has some initial charge.
Now the front panel assembly can
be gently lowered into the box and the
four small 10mm long self tappers used
to fasten the two together.
Your Altimeter/Mini Weather Station should now be complete and ready
to go. Charge the Li-Ion cell for a few
hours (via a USB cable, power supply
December 2017 31
Fig.7: a full-size front panel
artwork for the Altimeter/Weather
Station, ready to photocopy
(or download from siliconchip.
com.au/Shop/11/4482). We
printed ours on heavy, glossy
photographic paper. The idea is
that this label is mounted behind,
and visible through, the clear
acrylic laser-cut front panel, so it
is fully protected from, especially,
the weather (and grubby fingers!).
This label will normally be
held in place by the front panel;
however, a very fine dusting of
spray adhesive will hold it in
position while you drill the label
holes (all 3mm) and cut out the
Touchscreen Display rectangle
with a very sharp hobby knife.
or solar panel) before you turn on S1
again to put the project to work.
What it can do
When you turn it on for the first time,
you should get the weather station display shown in the photos.
The device will initially start up in
this mode, and will also have its altitude reference set to MSL (mean sea
level) and the altitude units set to metres – as indicated in the line of text
just below the Altitude reading.
At the bottom of the display you’ll
see a red button labelled “TOUCH TO
CHANGE MODE OR UNITS”.
And if you do touch this button, the
display will change into a one giving
you the options of changing to the alternative Altimeter display, changing the altitude units to feet instead
of metres (or back again), or changing
the altitude reference level from MSL
to the current ground level (or back
again). There’s also an “EXIT WITHOUT ANY CHANGES” button at the
bottom of this screen.
So if you want to change over to Altimeter mode, this is done quite simply
by touching the button at upper right,
labelled “ALTIMETER MODE”.
This will change the display over to
one showing just the altitude, in large
digits for high visibility. But the altim-
eter units and reference level won’t
have changed at this stage, so the text
just below the altitude digits will still
read ‘metres above MSL’.
If you’re happy with these settings,
fine. But if you’d rather have the altitude in feet rather than metres, simply
touch the button at the bottom of the
screen to bring up the ‘change options’
display again.
Then touch the button labelled
“FEET”, and you’ll return to the Altimeter screen with the reading shown
in feet rather than metres.
Here’s an important point to note,
though. If the altitude reference level
is still set to MSL, you may be getting
a negative altitude reading if the air
pressure in your vicinity happens to
be significantly higher than the nominal MSL level of 1013.25hPa (hectoPascals).
This can be a bit confusing, but
the problem is easily fixed by touching the button at the bottom of the
screen once again, and then touching
the “GROUND REFERENCE” button
at lower right on the ‘change settings’
display.
This will set the altitude reference
level to the current barometric pressure level; ie, the altitude at your current position.
This ‘ground reference level’ can be
So what is the Micromite – and what will it do for YOU?
We’ve made many references to the “Micromite” and the “Micromite BackPack” in
this article – after all, that is the platform
on which the Altimeter/Weather Station is
based.
The Micromite was developed in Australia
by Geoff Graham and has been used exten-
32
Silicon Chip
sively in SILICON CHIP projects and as a microcontroller platform in its own right.
It’s similar in some respects to other microcontrollers such as the Arduino, Raspberry Pi
etc.The Micromite has developed an enormous
following around the world, mainly due to its
ease-of-use and the fact that it uses “MMBASIC”
Celebrating 30 Years
reset at any time, simply by switching
to the ‘change settings’ display and
touching the “GROUND REFERENCE”
button again.
By the way whenever you change
any of the settings in the ‘change settings’ display, all of the setting parameters are saved in the Micromite’s
non-volatile memory. This means that
if you turn off the device power, next
time you power it up again the same
settings will be restored.
You can always change back from
Altimeter mode to Weather Station
mode, simply by touching the button
at the bottom of the screen and then
the “WEATHER STN MODE” button
at upper left.
Similarly, you can change the altimeter units to metres and the altimeter
reference level back to MSL.
One last point: as mentioned earlier, when fully charged, a single 18650
Li-Ion cell of decent quality should be
able to power the Altimeter/Weather
Station for between 3.8 and 8.75 hours.
This should be long enough for most
purposes, but don’t forget to charge it
up before going on a flight or journey.
When the cell’s voltage is falling to
the point where it’s no longer capable
of powering the unit, you’ll notice that
the display starts flickering.
Time to turn it off and charge it! SC
– a variant of the hugely popular and very
easy to understand BASIC language.
In past issues, we have prepared several
features on the Micromite and its peripherals, including some aimed at first-time users.
Log on to siliconchip.com.au, search for
“Micromite” – and enjoy!
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by Andrew Pullin
Interfacing
with the
Raspberry Pi
for Beginners
While the Raspberry Pi (RPi) micro computer is very popular and has a very
large user base, not too many people are aware that the RPi’s GPIO interface
can be used for some very interesting applications, such as driving fancy
graphics displays. As well, it can provide a user-configurable clock and can
interface easily with third party sensors and other equipment. Finding out how
to do this stuff is tricky though and this article will reveal how to go about it.
T
he Raspberry Pi was originally developed by the
Raspberry Pi Foundation, a UK Charity, to promote
the teaching of basic Computer Science in Developing Countries (see siliconchip.com.au/link/aagc).
But the popularity of the cheap, single-board computer
(SBC) has seen it explode onto the world market and its
uses are much wider than originally intended, including
as a powerful embedded controller.
The GPIO pins
The General Purpose Input Output (GPIO) connector of
the RPi is typically a 40-pin header on the board but there
is a little bit more to it than that. Some of the pins connect
directly to the central Broadcom BCM28xx System on a
Chip (SOC) IC. Some provide power supply rails and some
ground connections.
These pins are unfortunately not connected in an easy-toremember way. This is partly due to the fact that the slightly different Broadcom SOCs used in the various Raspberry
Pis have different interface circuitry.
This causes some compatibility issues between earlier
and later versions of the RPi.
The Raspberry Pi 1 Models A+ and B+, Pi 2 Model B, Pi
3 Model B and Pi Zero/Zero W have a 40-pin GPIO header
labelled J8. The original Raspberry Pi 1 Models A and B have
a 26-pin connector instead, with 14 connections missing.
To make things even more confusing, the Model B rev.
2 also has an extra 8-pin header labelled P5 on the board
(and for some reason, P6 on the schematics) offering access to an additional four GPIOs.
Another point of difference is that Models A and B provide access to the ACT status LED via GPIO pin 16 while
Models A+ and B+ provide the same access via GPIO 47
as well as the power status LED via GPIO 35.
GPIO pin assignments
For the moment though, let’s look at the 26/40-pin main
GPIO header. Fig.1 shows the pins on this header, numbered according to their position and colour-coded based
on their function.
The accompanying legend indicates the meanings of
these colours. Unfortunately, this is not how the pins are
Enlarged for clarity, this
shows not only the GPIO
header (the double row of
pins along the top, labelled
J8 on the PCB) but also
the identification of this
particular RPi (a Raspberry
Pi 3 Model B V1.2).
34
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Celebrating 30 Years
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HDMI
micro USB
Power
DSI Display Port
CSI Camera Port
Micro SD
(opposite side)
USB 2 Ports
Bluetooth 4.1
WiFi
GPIO Pins
Network
CPU, GPU, Memory
USB 2 Ports
An enlarged version of the Raspberry Pi 3, identifying the various interfaces. The one we are particularly interested in is
the row of 40 header pins (2 x 20) along the edge of the board, labelled GPIO (General Purpose Input Output) Pins. This
article gives a broad range of uses for the GPIO which you otherwise might not have been aware of.
actually mapped to the RPi processor.
This is shown in Fig.2 – ignore the shading for now and
just compare the pin numbering to Fig.1. As you can see,
it is quite different. The numbering scheme in Fig.2 shows
the RPi I/O pin number that’s connected to each pin on the
header (referred to below as the BCM pin number, which
is short for Broadcom).
This may seem a little confusing but in many cases, you
can simply connect whatever digital input/output that you
need to control to any one of these pins and then change
your software to communicate using the number shown
in Fig.2.
The good news is that this numbering scheme applies
to any RPi with a 40-pin GPIO header.
There are some cases where you need to use a specific
pin for a specific purpose, though. This is indicated by
the extra labels in Fig.2 and the shading around the outside of the pins, which shows how the pins are related in
terms of function.
The special functions include one UART, two SPI buses, two I2C buses, three PWM outputs and three square
wave outputs.
Fig.1: the pins on the GPIO header, numbered according to
their position and colour-coded based on their function.
siliconchip.com.au
In case you aren’t familiar with the acronyms:
UART stands for Universal Asynchronous Receiver/Transmitter and is basically a 3.3V bidirectional RS-232 serial port.
SPI is Serial Peripheral Interface, a higher speed (and simpler) bidirectional serial bus.
I2C stands for Inter-Integrated Circuit and is a slower serial
bus which only requires two wires (plus ground) and it
can be shared by multiple devices, unlike SPI or VART.
PWM stands for Pulse Width Modulation and allows you
to produce a square wave with a variable frequency and
duty cycle, eg, to control the brightness of LEDs, motor
speed and so on. The square wave/clock outputs are similar except that only their frequency can be varied; the
nominal duty cycle for these outputs is 50%.
These functions are shared with the general purpose
I/O pins, meaning the pins labelled with special functions
can be switched between normal inputs, normal outputs
or those dedicated functions. So if you want to use one of
Fig.2: the RPi I/O pin number that’s connected to each
pin on the header (referred to in the text as the BCM pin
number, which is short for Broadcom).
Celebrating 30 Years
December 2017 35
NOTE: URL “SHORTLINKS”
URLs (website addresses etc) in this feature have been
shortened to SILICON CHIP Shortlinks, saving you a lot of keystrokes (and mistakes!). In the online version, clicking on
these shortlinks will take you direct to the relevant website.
these functions, you will have to use a pin or set of pins
as indicated in this diagram.
Before we move on, here’s a hint: before hooking any
hardware up to the GPIO port, first figure out which of
these dedicated-purpose pins you need to use. You can
then use the remaining pins for other digital I/O tasks
without any conflicts.
Serial bus connections
UART connections are simple; TXD is the transmit pin
and RXD is the receive pin. You could arrange for two Raspberry Pis to communicate with each other by connecting
TXD on one to RXD on the other and vice versa, then making a ground connection between the two.
The I2C buses also have two pins but they have different purposes. SDA (SD) is the data pin and SCL (SC) is the
clock pin. All devices on an I2C bus have their SDA pins
joined together and their SCL pins joined together. On each
bus, there should be a single pull-up resistor between each
of these two networks and the 3.3V supply rail. The values
of these resistors depends on the bus speed.
For more information, see siliconchip.com.au/link/aagd
SPI buses have at least three pins. SCLK is the clock and
this is wired directly between the master and each slave
device on the bus. MOSI stands for “master out, slave in”
and MISO “master in, slave out”. Like SCLK, all identical
pins on the bus are joined together.
SPI bus zero has two additional chip enable/slave select
(CE) pins which can be wired to two separate slaves and
these are pulled low to indicate which slave the master is
communicating with at any given time.
You can have more than two slaves on the SPI0 bus but
then you will need to use additional GPIO pins, set as outputs (normally high) and pull them low manually before
initiating communication with that slave (and bring it high
when finished).
The SPI1 bus has three hardware CE pins, so you can
have one more slave than on SPI0 before you need to resort to manually driving the chip enable/slave select pins.
We have more details on using these serial buses below
but first let’s look at the other functions available on the
GPIO header.
Power supply rails
You can use some of the pins on the GPIO header to
power external circuitry. Pin 2 and 4 are both connected
to the 5V rail, which is normally directly connected to the
RPi’s power supply (typically a USB charger). Pins 1 and
17 provide a regulated 3.3V supply while pins 6, 9, 14, 20,
25, 30, 34 and 39 are ground connections.
These eight ground pins are all joined together by the
ground plane on the RPi so it doesn’t really matter which
one(s) you use for connecting either power supplies or as
a ground reference (eg, as part of a voltage divider).
However, you probably shouldn’t use the same ground
pin for both purposes. So use at least one dedicated ground
36
Silicon Chip
reference pin, while the others can be used as a supply rail.
In practice, when powering circuitry from one of the
3.3V or 5V pins, use the nearest ground pin to complete
the circuit.
Remaining GPIO pins
All pins, other than the power and ground pins, can be
used as either inputs or outputs. This is configured by the
software running on the Raspberry Pi. Pins that are not labelled with special functions in Fig.2 can only be used in
this manner while the other (special function) pins can be
used as inputs or outputs only if they are not being used
for their specific function.
You need to be wary when using the GPIO pins as inputs
since most of them have pull-ups or pull-downs built into
the Raspberry Pi. Referring to the pin numbers given in
Fig.2, those labelled 0-8 are pulled high by default while
the rest are pulled low. Note that the pins which are pulled
high include all four I2C pins plus both SPI-0 Chip Enable
pins, which makes sense when you consider their functions.
GPIOs which are configured as outputs can drive the digital inputs of other ICs or light LEDs if the current is limited
to what the Broadcom chip can handle (16mA each, 51mA
total). But they are not designed to drive anything directly
that requires high current like motors. Output current can
be boosted in various ways, such as by adding transistors
or using a third-party HAT (Hardware Attached on Top)
board which boosts the current capabilities.
Note also that any GPIOs which are driven externally
must not be driven below 0V or above 3.3V. This can damage the RPi. For signals which may exceed these limits, you
need to use either a series resistor and clamping diodes or
a level-shifter IC.
None of the RPi pins are 5V-tolerant.
If you need to communicate with a digital chip that uses
5V signalling, in many cases, a 3.3V output from the RPi
will successfully drive the input of the 5V device.
But you’d better check the device’s data sheet to make
sure that it will reliably read voltages above 3V as a high
level. For signals going from the 5V device to the RPi,
you’re best off using a level shifter IC such as the 40109B
although there are other approaches.
For pins which are programmed as digital inputs, the
software can read their value and this will return a value
of zero (when the voltage on that pin is low) or one (where
it’s at or near 3.3V). Similarly, for pins set as digital outputs,
the software can set their value to zero, in which case the
voltage will be pulled down to around 0V, or one, in which
case the pin’s voltage will be pulled high, close to 3.3V.
So that covers the basics of RPi GPIO and you can find
tutorials on the internet which show you how to program
the I/O pins as digital inputs or outputs. But the devil is
in the detail and those details are what makes the RPi really useful.
Alternative pin functions
The Raspberry Pi Organisation website (siliconchip.com.
au/link/aagc) has some very useful information on it about
everything Pi but it is sometimes hard to find the more technical information unless you know where and what to look for.
Often, it is simpler to just Google for information elsewhere to find it, then search the Pi site separately. Having done the above, I discovered a very useful website at
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siliconchip.com.au/link/aage
This website provides all the pinouts of the GPIO on the
Raspberry Pi and here is where the first surprise comes from.
A hidden graphics display function
The GPIO header can do more than one thing if you know
how and where to look for the information. The first thing
I learned was that the GPIO can be used as an up to 24-bit
colour display driver called the Parallel Display Interface
(DPI). The details for the DPI can be found at: siliconchip.
com.au/link/aagf In a nutshell, this interface can be used
to drive an RGB display using one of three formats;
• RGB24 (8-bit red, 8-bit green and 8-bit blue),
• RGB666 (6-bit red, 6-bit green and 6-bit blue) or
• RGB565 (5-bit red, 6-bit green and 5-bit blue).
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The DPI is controlled by the Graphics Processing Unit
(GPU) part of the Broadcom SOC and is user configurable
via a simple text file in the Linux Operating System that’s
typically used on the RPi.
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User-configurable clocks
There are three user-configurable General Purpose Clock
(GCLK) pins on the GPIO header. These signals are derived
from the peripheral clock sources via clock generators with
MASH (multi-stage noise shaping) dividers. These allow
the GPIO clocks to produce audio signals.
Wow! That was unexpected. I can see the need and use
for some kind of clock interface on the GPIO interface but
to have the capability to drive audio devices out of the box
is pretty powerful.
As shown in Fig.2, the Clock Pins on the GPIO header are:
• Pin 7 (BCM 4): GCLK0
• Pin 29 (BCM 5): GCLK1
• Pin 31 (BCM 6): GCLK2
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This one is pretty technical and very confusing for beginners, especially since it lies and actually needs two
wires (one for data and one for ground). Basically, this is
used in a very simple master/slave configuration to communicate with certain devices such as the DS18B20 digital temperature sensor.
The default pin used for this protocol is pin 7 on the
GPIO header (BCM 4) but this can be changed. If you are
interested in doing this, refer to our article titled “1-Wire
Digital Temperature Sensor for the Raspberry Pi” in the
March 2016 issue (siliconchip.com.au/Article/9849) which
has all the details.
Pulse Code Modulation (PCM)
PCM is a digital representation of a sampled analog signal. The Raspberry Pi can produce this form of digital audio
output which can be fed to a Digital to Analog Converter
(DAC) for high quality sound. The output signal from a DAC
chip is normally a couple of volts but with only a weak
drive strength so it will probably need to be fed to an audio amplifier before it can power headphones or speakers.
You can also use this PCM interface to connect to a highspeed ADC (analog-to-digital converter), ie, the opposite
of a DAC. Or you can even use it with a CODEC, which is
basically a synchronised DAC and ADC in one package.
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The PCM function is available on the following four pins:
•
•
•
•
Pin 12 (BCM 18): PCM CLK (Clock)
Pin 35 (BCM 19): PCM FS (Frame Synchronisation)
Pin 38 (BCM 20): PCM DIN (Data In)
Pin 40 (BCM 21): PCM DOUT (Data Out)
There are a number of tutorials on how to use this PCM
interface on the Internet. This one from AdaFruit is useful: siliconchip.com.au/link/aagg
Note that CLK is the bit clock and there will be one pulse
on this line for every bit transmitted to the DAC (DOUT)
or received from the ADC (DIN). The FS pin will typically produce one pulse for every set of samples transmitted
and/or received. In the case of a stereo DAC/ADC/CODEC,
this is one pulse for every pair of samples (ie, left and right
channels) and the current polarity of the FS signal indicates
which channel is being transmitted/received.
Depending on the sampling rate and resolution, these signals can have quite high frequencies; up to around 24MHz.
So signal routing can become an issue.
Inter-Integrated Circuit (I2C) details
I2C is a serial communication protocol originally developed by Philips Semiconductor to enable simple low
level communication between chips and uses two wires
plus ground, as described earlier. It is now a communication standard in the computing world for sensors, microcontrollers, port expanders and more.
Sensors! Microcontrollers! Now we are talking.
I2C is supported by a large range of devices, especially
devices which don’t need to get a lot of data in or out; this
is one reason why most sensors support I2C. You can also
use I2C to communicate with another micro, however, this
will be slower than if you use SPI (as described below).
The primary I2C port on the RPi is I2C1 and uses the
following two pins:
• Pin 3 (BCM 2): I2C1 SDA (data)
• Pin 5 (BCM 3): I2C1 SCL (clock)
As the I2C Pins on the GPIO port have built-in pull-up
resistors, you don’t need to add external resistors for normal low-speed signalling. However, you may need to add
extra pull-up resistors for higher speeds.
Again, there are some very good tutorials on the Internet
and if you are serious about using your RPi then learning
as much as you can about I2C cannot be a bad thing. Try
this one: siliconchip.com.au/link/aagh
There is a second I2C port (known as I2C0) on the following pins:
• Pin 27 (BCM 0): I2C0 SDA (EEPROM Data)
• Pin 28 (BCM 1): I2C0 SCL (EEPROM Clock)
As a beginner, I would strongly advise that you do not
use I2C0. The reason for this is that it is wired up directly
to the EEPROM on the RPi. An EEPROM is an Electronically Erasable Programmable Read Only Memory.
The one on the RPi can be wiped and reprogrammed
using these GPIO pins and that could make your RPi less
useful than a brick if you don’t know what you are doing.
Don’t say I didn’t warn you!
Serial Peripheral Interface (SPI) details
The SPI is also known as the four-wire serial bus and
38
Silicon Chip
Shown here for comparison and identification, these
are the front (above) and rear (opposite) views of the
Raspberry Pi Model 3 micro PCBs.
allows you to do some really cool things. One of the most
common uses of SPI is to communicate with other devices like Arduinos, enabling you to load Sketches directly
into them.
As described earlier, there are two SPI buses available on
the 40-pin GPIO. The first one, SPI0, uses the following pins:
•
•
•
•
•
Pin 19 (BCM 10): SPI0 MOSI (Master Out, Slave In)
Pin 21 (BCM 9): SPI0 MISO (Master In, Slave Out)
Pin 23 (BCM 11): SPI0 SCLK (Serial Clock)
Pin 24 (BCM 8): SPI0 CE0 (Chip Enable/Slave Select 1)
Pin 26 (BCM 7): SPI0 CE1 (Chip Enable/Slave Select 2)
The second port, SPI1, is on:
•
•
•
•
•
•
Pin 38 (BCM 20): SPI1 MOSI
Pin 35 (BCM 19): SPI1 MISO
Pin 40 (BCM 21): SPI1 SCLK
Pin 12 (BCM 18): SPI1 CE0
Pin 11 (BCM 17): SPI1 CE1
Pin 36 (BCM 16): SPI1 CE2
One of the things that make the SPI peripherals so versatile is that they have several “master modes” which allow communications with different kinds of chips. The
first mode is “Standard Mode” which is the normal 3-wire
protocol (not including chip select or ground).
The second is “Bi-Directional Mode” which uses one
less wire. MISO is not used and MOSI instead functions
as MOMI (Master Out, Master In) where it functions as either MISO or MOSI depending on whether data is being
transmitted or received.
The third mode is “LoSSI Mode” which stands for Low
Speed Serial Interface. This is a 9-bit communications
mode typically used to interface with small LCD screens.
A great explanation of all these modes is available on
the Raspberry Pi Foundation website here: siliconchip.
com.au/link/aagi
UART serial port details
As we said earlier that a UART is typically used for RS232 communications.
The U for Universal means that transmission speed and
data format are configurable.
As it is an asynchronous serial port, there is no need for a
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nisation clock). For the two possible pin assignments for
each of these functions, see the link above.
Further information
The Broadcom BCM2835 SOC was used in the original
RPi Model A1/1+ and Model B1/1+; the BCM2836 on the
Model B2; and the BCM2837 on the Model B2v2.1 and
Model B3.
All of these SOCs are backwards-compatible with
the BCM2835 and a large amount of very technical and very useful information can be found
in the BCM2835 ARM Peripherals Datasheet at:
siliconchip.com.au/link/aagl
No analog inputs or outputs
With the exception of the micro SD socket (right side of the
PCB) there is virtually no connection made to the rear of
the PCB.
separate clock signal and so two wires can be used for full
duplex communications (simultaneously transmitting and
receiving data).
This type of serial port has been used for decades to get
different devices to talk to each other.
Back in the 1980s, I used to work at a Cabling Company
in Adelaide and I had a book with about 100 different serial port configurations and how to wire them up. It impressed me back then and not much has changed. The pins
used for UART are:
• Pin 8 (BCM 14): TX/TXD (transmit)
• Pin 10 (BCM 15): RX/RXD (receive)
Since we also need a common ground, there is a convenient one at pin 6. A good general discussion of serial
communications on the RPi can be found here: siliconchip.
com.au/link/aagj
JTAG
Most 32-bit and 64-bit microprocessors support an interface known as JTAG which stands for “Joint Test Action
Group”. This can be used for programming and testing various chips and the chips can be chained together so that
a single JTAG interface can be used to communicate with
all of them, simplifying circuit board layout.
As well as programming chips, JTAG can be used for
“boundary scan”, which allows a device to inspect and
possibly change the state of the pins on an IC. For debugging, the JTAG interface can provide one or more “test access ports”.
Note that using a JTAG interface generally requires complex and quite specialised software and while we have
successfully used it to program some devices, it really is a
lot of work to get up and running (and beyond the scope
of this article).
If you want to know more then Google is your friend.
This is a very good tutorial for debugging a Raspberry Pi
using JTAG but we have to warn you that it’s heavy going:
siliconchip.com.au/link/aagk
The RPi has two possible sets of JTAG pins, with only
the TRST (test reset) function fixed to BCM pin 22. The
other JTAG functions are TDI (data in), TDO (data out),
TCK (clock), TMS (test mode select) and RTCK (synchrosiliconchip.com.au
There is only one sticky point about the RPi GPIO compared to other micros and this is that the “out of the box”
version has no analog inputs or outputs.
This is an issue because there are a multitude of sensors
available on the market and not all of them have a digital
output so you can’t directly connect them to the Pi. The
operating word here is “directly”.
The Pi can create analog signals (sort of) by using PWM
and then passing this signal through a low-pass filter but
that’s pretty crude and only works well in certain situations. You can use the PCM interface described above with
a DAC but that requires quite a few extra components.
The most common solution for analog I/O is to plug in
a HAT board designed for this purpose. (HAT stands for
Hardware Attached on Top).That is certainly an easy way
to do it, but of course HATs cost money and so the Community has been hard at work problem solving and come
up with a few ideas of its own.
While it is of limited use, you could consider combining
an external comparator with the PWM or PFM functions to
form a “Poor Man’s ADC”, as described here: siliconchip.
com.au/link/aagm
Another common method is to use an off-the-shelf ADC
module such as one with the MCP3004/3008 and interface
to it using the GPIO pins.
One of the great things about the MCP3004/3008 is that
they have built-in SPI interfaces. A tutorial showing how
to do this can be found at: siliconchip.com.au/link/aago
How to access GPIOs through software
There are a few different ways to control the GPIO pins
from software on the RPi. Some are supplied with the RPi
operating system and some are from third parties.
The Raspberry Pi Foundation recommends running the
NOOBS operating system, which is a custom-built version of Linux.
But it is not the only operating system available. There
are several versions of Linux, Windows 10 IoT Core and
one called RISC OS. If you’re using the recommended
NOOBS, you will already have most of the software libraries that you need.
The Raspberry Pi Foundation recommends using the
Python programming language that comes standard with
NOOBS and the C language is also very common; it too
comes standard.
Each of the many tutorials I discovered had various libraries and technologies to install depending upon the application, but one such common library is WiringPi, which
Celebrating 30 Years
December 2017 39
can be found at siliconchip.com.au/link/aagn
According to their web page, “WiringPi is a pin- based
GPIO access library written in C for the BCM2835 used in
the Raspberry Pi. It’s released under the GNU LGPLv3 license and is usable from C, C++ and RTB (BASIC) as well
as many other languages with suitable wrappers. It’s designed to be familiar to people who have used the Arduino
‘wiring’ system.”
Beginners may find Python programming easier. We published an article in the November 2016 issue titled “Using
your Raspberry Pi with a smart-phone as WiFi-controlled
switch” (siliconchip.com.au/Article/10416).
It gave detailed set-up procedures and sample code which
shows how to control some GPIO outputs from a Python
web script. That code could be adapted to perform other
tasks quite easily.
If you are familiar with C/C++ then we suggest that you
install WiringPi and give it a go. After that, the sky is the
limit.
Conclusion
While Raspberry Pi was intended as a low-cost computer
for educational purposes, the GPIO port also gives users the
ability interface the Pi to the real world quickly and easily.
I now have two Raspberry Pis and a couple of Arduinos
and what started out as a simple search to learn a bit more
about how to make them talk to the world has ended up
as this article.
I hope readers can get use it as a jumping-off point for
their own projects based on the Raspberry Pi.
References
• A general overview of the Raspberry Pi from Wikipedia:
siliconchip.com.au/link/aagq
• Official GPIO documentation: siliconchip.com.au/link/
aagr
• Comprehensive GPIO Pinout guide for the Raspberry Pi:
siliconchip.com.au/link/aags
• Compute Module I/O pins: siliconchip.com.au/link/
aagt
• Display Parallel Interface details:
siliconchip.com.au/link/aagu
• BCM2835 ARM Peripherals Datasheet from Broadcom,
2012 (PDF): siliconchip.com.au/link/aagv
• Raspberry Pi debugging with JTAG (PDF):
siliconchip.com.au/link/aagw
• Pulse Code Modulation interface:
siliconchip.com.au/link/aagx
• I2C with Raspberry Pi: siliconchip.com.au/link/aagy
• SPI with Raspberry Pi: siliconchip.com.au/link/aagz
• Using UART on Raspberry Pi with Python:
siliconchip.com.au/link/aah0
• GPIO Interface library for the Raspberry Pi:
siliconchip.com.au/link/aah1
• MCP3004/3008 4/8-channel 10-bit ADCs data sheet
(PDF): siliconchip.com.au/link/aah2
The RPi website, raspberrypi.org, has a wealth of
information and references to help you on your way.
40
Silicon Chip
The Raspberry Pi 3 is distributed in Australia by element14.
See siliconchip.com.au/link/aagp It is available through a
number of retailers including Altronics and Jaycar.
SC
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The Altronics Mega Box
Article by
Bao Smith
T
Make your
Arduino projects
easier to build and look much
more professional with this kit from
Altronics. It includes a pre-cut plastic instrument
case, 16x2 alphanumeric LCD, four illuminated pushbuttons,
two relays, an infrared receiver, rotary encoder and pluggable terminal
blocks. This makes building your Arduino Uno or Mega project a breeze.
he Altronics MegaBox kit (Cat
K9670; www.altronics.com.
au/p/k9670-inventa-mega-box-forarduino/) is a clever Arduino prototyping system developed by Altronics.
It comes with a large PCB measuring
197 x 115mm and the Arduino module and optional shield board plug into
this. The PCB then neatly fits into the
supplied case with the controls accessible through holes cut into the front.
It’s easy to build since all the components are through-hole types. While
we describe it as a prototyping system,
it’s quite possible to build a finished
project using it; something that would
come in handy everyday.
As well as the extra components
mentioned above which you can use
to build your project, the PCB has a
210-pin prototyping area which lets
you fit the extra components you need
which are not already provided by the
MegaBox or fitted to the Arduino or
shield boards.
All the connections from the main
Arduino board and the other hardware in the box are broken out into
female headers so that you can easily
make connections between them using jumper wires.
The MegaBox also has a lot of extra power supply connection points,
which you will often find you need.
For example, near where the Arduino
module is mounted, there are four sets
42
Silicon Chip
of five sockets giving you additional
3.3V, 5V, GND and VIN connections.
Similarly, there are two 14-pin headers
near the prototyping area, one giving
you access points to the 5V rail and
the other GND.
Due to the way the boards are
mounted they provide a separate 6-pin
in-circuit serial programming (ICSP)
connector. Then you have connection
points to attach wires for interfacing
with other components like the illuminated pushbuttons, relays, LCD, LEDs,
rotary encoder and infrared receiver.
Note that to take full advantage of
all the features in the MegaBox, you
really need to use an Arduino Mega to
have enough I/O pins. But you certainly can use it with an Uno for some applications and this is how we tested it.
What can it be used for
When you plug a shield board into
an Arduino, you can play around a bit
but all you’re really left with is a bit of
a curiosity. To turn it into something
truly useful, you need a user interface
for your device, some kind of enclosure and so on. The MegaBox gives
you all that.
For example, you may recall the article in our July 2017 issue on building
the Arduino Music Player (See www.
siliconchip.com.au/Article/10722).
We plugged an MP3 player shield
into an Arduino Uno but to make it
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truly useful, we had to add a keypad
and an LCD so you could control it.
And while that worked well, all you
ended up with was three separate modules connected by flying leads; hardly
a “finished product”.
If we had the MegaBox, we could
have easily built that finished product
and with a lot less hassle. In fact, you
could take our Arduino Music Player
code and adapt it to the MegaBox, giving quite a nice little package.
It already has an LCD module onboard and since it has a remote control
receiver too, you could use a universal
remote to control it. That’s even more
convenient than the numeric keypad
we used at the time.
You could also use the four illuminated pushbuttons to provide standard functions such as play, stop, pause
and next/previous track, and the rotary encoder to scroll through menu
items. The more we think about it,
the more we realise that adapting the
code in this manner would be a really
fun project!
You may also remember our Arduino-based Digital Inductance and Capacitance Meter from the June 2017
issue (see www.siliconchip.com.au/
Article/1067). Guess what – Altronics
have actually designed a shield board
for that project and it integrates perfectly with the MegaBox.
We don’t have space to describe it
siliconchip.com.au
The Altronics MegaBox connected and running the provided example program. The illuminated pushbuttons are
controlled via an IR remote control, and the LCD backlight brightness is adjusted by the rotary encoder, with an integer
value displayed on the screen indicating the number of units away from the rest position of the rotary encoder.
fully in this article but we’ll show how
to build it and integrate it with the
MegaBox (or separately) next month.
Those are just two examples of what
you can do with the MegaBox. Given
the plethora of Arduino shields, the
hardware provided by the MegaBox
itself and the ability to add extra components in the prototyping area, it’s a
really flexible system that would be
suitable for a lot of different purposes.
Circuit description
The MegaBox circuit is shown in
Fig.1. Much of this is taken up by the
Arduino module, the optional shield
and the wiring between them.
The headers where the shield can
be plugged in are wired directly to
the corresponding pins on the Arduino, which is also plugged into a set of
headers. So the shield works as if it’s
plugged on top of the Arduino board,
even though the two are mounted
side-by-side.
A third set of headers, shown next
to the ones the Arduino is plugged
into, are provided so that it’s easy to
wire up any free Arduino pins to other
parts of the board.
Most of the rest of the circuitry is in
separate blocks with headers for the
inputs and/or outputs of each block.
So to use one of these sub-circuits, all
you have to do is run jumper wires
between the Arduino headers and the
headers for that sub-circuit.
One of the few portions of circuitry
already wired to the Arduino itself
surrounds LED3, which lights up
when the SCK pin is high, indicatsiliconchip.com.au
ing that SPI serial communication is
in process.
LED3 is driven by NPN transistor
Q4 which is in turn driven by pin 13
(the SCK pin on the Arduino Uno)
via a 10kW current-limiting resistor. A
second 10kW base pull-down resistors
shunts any leakage current to ground.
There’s also a reset pushbutton (S5)
on the MegaBox board because the
button on the Arduino itself is inaccessible due to being mounted upsidedown. This is simply wired between
the Arduino reset pin and ground.
Headers CON3-CON6 provide an
easy way to access the 3.3V, 5V and
VIN (DC input) supply rails and make
ground connections. Each provides
five sockets to make connections to
one of these rails.
Separate sub-circuit blocks
Pushbuttons S1-S4 are illuminated
momentary types; the illumination
is provided by a built-in LED. Three
headers are provided to make connections to these buttons.
One 8-way header (CON2) gives
access to the LED anodes via 1kW current-limiting resistors; the cathodes
are connected to ground. That same
8-way header also gives access to the
switch common terminals.
Two additional four-way headers
This is what the PCB should look like after all the soldering has been completed.
Three of the 3-way screw terminals do not have a matching relay, so you will
need to solder wires to the adjacent pins to utilise them. Also, you can see that
digital pin 3 of the Arduino main board is mislabelled on the PCB.
Celebrating 30 Years
December 2017 43
Fig.1: complete circuit diagram for the Arduino MegaBox.
(CON17 & CON18) are provided to
connect to the normally open and normally closed contacts plus there are
four jumpers (JP1) to short the normally-open contacts to ground.
This makes it easy to sense when a
44
Silicon Chip
button is pressed since all you need
to do is fit the shorting block on the
jumper for a button and then wire the
same button’s common terminal to an
Arduino digital pin. Set that pin as a
digital input with internal pull-up and
Celebrating 30 Years
the pin will be high normally and is
pulled low when the button is pressed.
Two extra general purpose LEDs,
LED1 and LED2, are provided and
would be most useful for debugging
purposes since they are mounted insiliconchip.com.au
lows you to wire these relays up to
Arduino pins.
There are also three extra 3-way
pluggable terminal blocks at the back
of the unit which are wired to solder
pads on the board and you could potentially wire these up to extra circuitry fitted to the prototyping area.
An infrared receiver is mounted at the front of the unit and it is
powered from the 5V supply, with a
47W/47µF RC filter to prevent supply noise from affecting its operation. Its output is available on a
1-pin header (IR interface) and the
signal can be decoded using the
Arduino IRLib or other library.
There is provision for mounting a
16x2 LCD panel on the front of the unit
and its 16 pins are wired directly to
a 16-pin female header (CON9). The
power supply (+5V and GND) pins are
pre-wired for you along with contrast
adjustment trimpot VR1.
Transistor Q3 allows PWM control
and dimming of the backlight and it
has a 1kW base current-limiting resistor and a 10kW resistor to ensure it
stays off when not driven.
A rotary encoder (similar to a potentiometer but with a digital output) is
provided for user input and is wired
to a 2-way header (Encoder interface)
with 10kW pull-ups to 5V on its two
output terminals. It provides a “graycode” output.
When rotated in one direction, the
binary output at terminals A & B will
have the following sequence: 00, 01,
11, 10, 00, 01, 11, … while rotation in
the other direction will give: 00, 10,
11, 01, 00, 10, 11, … There are various Arduino libraries to help you decode this, including one called (predictably) “Encoder”.
Construction
side the case. These are also provided with 1kW current-limiting resistors
and have their cathodes connected
to ground and their anode connections made via a 2-way header (LED
interface).
There are also two on-board DPDT
relays. One set of contacts for each
siliconchip.com.au
relay is wired to a 3-way pluggable
terminal block at the back of the unit.
Each relay has a back-EMF quenching diode across its coil and a BC548
transistor to drive that coil, along
with 1kW base current-limiting resistors and 10kW pull-down resistors. A
two-way header (Relay interface) alCelebrating 30 Years
The main task when building the
MegaBox is soldering all the components onto the main PCB. Fig.2 shows
the overlay diagram which indicates
where all the components go. Many of
them are headers (mostly female but
some male too).
Our sample MegaBox didn’t come
with much in the way of instructions
and if yours doesn’t either then this
article should be a useful guide. You
can also refer to our photos to see how
the finished board should look.
Start by soldering all the low-profile
components first (eg, resistors and diodes) then move on to the relays, semiDecember 2017 45
Fig.2: exact-size PCB overlay for the Altronics MegaBox, which shows the
locations of the various headers and other components.
conductors and capacitor. Some components, such as the diodes, capacitor
and relays, need to be fitted the right
way around. For the diodes and relays, match up the stripe/line on the
component to the one shown in Fig.2
or on the PCB.
For the three LEDs, the cathode
(shorter lead) is on the same side as
the flat portion of the plastic lens and
should be matched up with what is
shown in Fig.2 and the PCB silkscreen.
On the single 47µF electrolytic capacitor, the stripe down its side indicates the negative lead while the positive lead will be longer. The longer
(positive) lead goes to the pad marked
with the “+” symbol.
We found it easier to fit the switches, terminal blocks and infrared sensor
before the headers and left the rotary
encoder for last.
Note that the headers supplied may
be longer than needed and you will
have to cut the female headers to length
and snap the male headers apart.
The various different header lengths
required are listed in the parts list
46
Silicon Chip
while the headers supplied are likely
to be 40 pins long and so you can cut
these up to form several of the smaller headers. You will be left with some
spare headers at the end.
To snap the male headers, grab either
side of the location where you want to
snap them with two pairs of pliers (or
just one pair) and then apply force to
bend the header until it snaps. Doublecheck you will get the right number of
pins before snapping.
The female headers are a little more
tricky because you need to cut them
apart using side cutters. This almost
always destroys one pin so you should
make the cut in the middle of the pin
past the end of the last one you want
to keep.
You can then remove the pin at the
cut (if it didn’t already fall out) and
file any jagged plastic edges smooth.
Three dual-row female headers are
required and while Altronics do provide a long dual-row header to cut
apart, doing so is quite tricky; you really need a large pair of side-cutters.
Instead you can cut and fit two singleCelebrating 30 Years
row headers side-by-side.
Soldering the pin headers so they're
straight can be tricky. Our tip is to
solder one pin, then visually check it
is flush and straight and re-melt the
joints if it isn’t, while applying a small
amount of pressure.
Once it’s straight, you can solder the
other pins. You may also find that it
helps to use a small flat piece of wood
or similar material to support the header during soldering.
The right-angle female header is
used as the socket for the LCD but note
that you will have to solder a 16-pin
male header to the back of the LCD
panel to plug into this.
When soldering the rotary encoder,
be sure to solder the two support pins
on either side to prevent it from being
ripped off the board.
An example program
Altronics provides a small example
program on their website that showcases the LCD screen, rotary encoder,
IR sensor and four illuminated pushbutton switches. You can download it
siliconchip.com.au
from http://download.altronics.com.
au/files/software_K9670.zip
This program assumes you're using
an Arduino Mega for the pin layout;
you can use an Arduino Uno, like we
did, but some of the I/O pin numbers
will need to be changed. Here are the
pin numbers we used with their software to work with the Uno:
• Encoder interface: pin A → D2,
pin B → D3 (line 35)
• LCD screen: RS → D4, E → D5,
DB4 → D6, DB5 → D7, DB6 → D8,
DB7 → D9
• Backlight interface → D10 (line 46)
• IRD1 → D11 (line 53)
• SW1 LED → A3, SW2 LED → A2,
SW3 LED → A1, SW4 LED → A0
(lines 60-63)
Before you can compile and upload
the software in the Arduino IDE, you
will need to install third-party libraries from the following sources:
https://www.pjrc.com/teensy/td_
libs_Encoder.html
https://www.pjrc.com/teensy/td_
libs_IRremote.html
You might run into conflicting
names for the IRremote library as the
header file shares the same name as
the RobotIRremote library.
The easiest way to solve this problem without renaming one of the
libraries is to just remove the RobotIRremote library from "C:\Program Files\
Arduino\libraries" (or wherever the
Arduino IDE is installed) temporarily. That’s assuming it was already installed. Otherwise, it won’t be an issue.
With the libraries loaded, you can
upload the program to your Arduino
board using a type-B USB cable and
then make the various pin connections
using male-male flying jumper leads
(not included in the kit but see parts
list for a suitable set from Altronics).
It helps to have a variety of lead
lengths for tidiness but you will at
least need a few that are more than
100mm long, if not 200mm to match
the width of the PCB.
To figure out where the wires go, first
refer to the list of connections above
in reference to changes to the software
(which is a complete list) but you can
also refer to the photos in this article
as a guide.
Note that when you run the software, you will need to adjust contrast
trimpot VR1 for text to be visible on the
LCD. We found that we had to wind
it almost fully anti-clockwise for the
text to be visible.
siliconchip.com.au
Parts List
1 double-sided PCB, coded K9670, 196.5 x 115mm
1 quarter-rack plastic instrument case with pre-cut holes
1 16x2 alphanumeric backlit LCD screen (LCD1)
1 infrared receiver (IRD1)
4 right-angle illuminated momentary pushbutton switches (S1-S4)
1 4-pin PCB-mount vertical tactile switch (S5)
1 10kW horizontal trimpot (VR1)
2 2A 5V mini DIL DPDT relays (RLY1,RLY2)
5 3-way PCB-mount right-angle pluggable terminal blocks (CON8,CON12)
1 rotary encoder with nut, washer and knob (S6)
1 2x18 pin dual-row female header
1 2x14 pin dual-row female header
2 2x3 pin dual-row female headers
1 16-pin right-angle female header (CON9)
1 16-pin female header (CON16)
2 10-pin female headers
8 8-pin female headers (including CON2)
1 6-pin female header
4 5-pin female headers
2 4-pin female headers
3 2-pin female headers (including CON7)
2 1-pin female headers
1 2x18 pin dual-row male header
1 2x4 pin dual-row male header (JP1)
1 2x3 pin dual-row male header
1 16-pin male header (for LCD1)
1 10-pin male header
5 8-pin male headers
solder
plus mounting screws and rubber pads for the case.
recommended: Arduino Uno or Mega; set of various male-to-male single
jumper wires (try Altronics P1016); universal infrared remote control (eg,
Altronics A1012); 4 shorting blocks (for JP1). All not included in the kit.
Semiconductors
4 BC548 NPN transistors (Q1-Q4)
2 5mm red LEDs (LED1,LED3)
1 5mm green LED (LED2)
2 1N4004 1A diodes (D1,D2)
Also, note that their software doesn’t
adjust the LCD backlight until you turn
the rotary encoder. You could connect
the backlight control pin directly to
5V so that the backlight runs at full
brightness all the time (as long as the
unit is powered).
Or you can remedy this by adding
the line "analogWrite(BL, 255);" after
the line 69, which reads "lcd.begin(16,
2);". This will cause the backlight to
start out at its highest brightness (if
you haven’t wired it directly to 5V, as
suggested above).
The data sheet for the LCD screen
used in this project is available from:
siliconchip.com.au/link/aahx
The sample software will detect
rotation of the front-panel encoder
and display the rotation amount on
the screen.
It will also pick up and display some
infrared remote control codes, specifically, RC5 codes 0x001 - 0x004 and
0x801 – 0x804. These correspond to
the buttons 1-4 on a universal remote
Celebrating 30 Years
Capacitors
47µF 16V electrolytic
Resistors (all 1/4W, 1% metal film)
7 10kW (brown black black red brown)
10 1kW (brown black black brown brown)
set on one of the more common Philips
TV codes.
When these buttons are pressed
and are generating the correct codes,
it will toggle on/off the corresponding LED in one of the four pushbutton switches.
Conclusion
The Altronics MegaBox is a very
flexible system and can be used with
virtually any Arduino shield (apart
from a few that are too tall to fit in
the case). Altronics supply a range of
shields but it can be used with shields
from other sources, too.
Building the MegaBox is not difficult so it’s suitable for relative beginners. You can purchase the MegaBox
kit (K9670) for $80 plus postage, or
$75 each if you're buying two or more.
It is available from the Altronics
website at www.altronics.com.au/p/
k9670-inventa-mega-box-for-arduino
or you could pick the kit up from one
SC
of their retail stores.
December 2017 47
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Tel: (03) 8791 6300 Fax: (03) 9701 0177
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DJI, the world’s leader in civilian drones and aerial imaging technology, has
unveiled AeroScope, its new solution to identify and monitor airborne drones
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Tel: 1300 090802
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tional environments.
OKW’s new enclosure Applications web page for engineers
OKW has added a new Applications section to its website to help design engineers
specify the best enclosures for their electronics.
Each of the eight application sector includes a range of examples showing how
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Examples feature links to the standard
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Technology featured in the new Applications section spans the range of OKW products: wearable, handheld, wired, wall mount
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OKW’s customisation services are available even for low volume batches. Customers can specify bespoke colours, EMC shield48
Silicon Chip
SuperHouse:
Aussie DIY
home automation channel
If you want to learn how to
hack your house using Arduino,
ESP8266, ESP32, Raspberry Pi and
other common parts, have a look at
the SuperHouse Automation channel on YouTube.
Most home automation videos on
YouTube are just product reviews
and showing you how to use commercial gadgets.
This channel is different: hosted
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Oxer, it shows his ongoing journey
to hack every aspect of his house
and turn it into a SuperHouse.
Jonathan doesn’t just show the
end result. He works through the
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designs his projects and how they
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He releases his designs and
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Topics covered include custom
light switches, RFID, home automation system architecture, switchboard automation, MQTT, Powerover-Ethernet, CCTV, electronic
door locks, electric window mechanisms, security sensors, robot lawnmowers, and watchdog timers.
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Contact:
Rolec OKW Australia/New Zealand
PO Box 806, Penrith NSW 2751
Tel: (02) 4722 3388
Website: www.okw.com.au
Celebrating 30 Years
Contact:
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XC-4410
ELECTRONICS KITS
Great way to teach kids the fundamentals.
v
XC-4380
AB-3440
XC-4983
SNAP ON KITS
Bright pieces. Easy snap together. No tools or soldering. Ages 8+.
SHORT CIRCUITS BOOK VOL.1
AND PROJECT KIT KJ-8502
Kit includes baseboard, springs and components
to make 20+ projects, and 96-page coloured
Short Circuits Vol. 1, which is complete with
comprehensive assembly instructions and a full
technical discussion explaining exactly how the
circuit works. No soldering required.
$
$
3995
12 95
Batteries
not included
34-IN-1 KIT KJ-8983
Build up to 34 projects including electric
fan, FM radio and learn parallel and series
circuits. Requires 4 x AA batteries.
Batteries not
included.
$
29 95
$
69 95
698-IN-1 KIT KJ-8985
Build you own helicopter, alarm clock,
lighthouse, sound effects and more.
50 piece kit. Requires 4 x AA batteries.
Batteries not
included.
$
2795
ELECTRIC CURRENT
EXPERIMENT KIT KJ-8901
12-IN-1 ELECTRICAL
EXPERIMENT KIT KJ-8919
Learn the common principles of electric
current and magnetism. Requires 2 x D
batteries, scissors, and tape. Ages 8+.
12 different experiments to construct that
demonstrate various electronic principles.
Requires 2 x AA batteries. Ages 8+.
To order phone 1800 022 888 or visit www.jaycar.com.au
$
14 95
FM RADIO KIT KJ-8978
Create a fully functional selectable
FM radio with this simple snap on kit.
Requires 2 x AA batteries.
See terms & conditions on page 8.
$
15 95
BURGLAR ALARM KIT KJ-8974
Create burglar alarms and learn various
circuits designs. Requires 2 x AA batteries.
Page 51
EXTRA TECHY GIFTS FOR CHRISTMAS
CAR
HOME OFFICE
$
AC600 OUTDOOR
ROUTER YN-8349 WAS $119
FROM
39
95
Provides Wi-Fi access in your
outdoor entertaining area,
carpark, shed etc. Dual band
for speed up to 433Mbps.
Single PoE connection.
Functions as Wi-Fi repeater,
access point, or router.
Dual-Band
NOW
DUAL BAND WIRELESS
NETWORK ADAPTORS
149
$
159
$
SAVE $10
6/12/24V 15A BATTERY CHARGER 140A DUAL BATTERY ISOLATOR
KIT WITH WIRING MB-3686 WAS $159
MB-3623
Suitable for gel and lead acid batteries.
Microprocessor controlled for automatic
4-stage charging, including float charge.
Safe to leave connected without risk to
the battery.
• 5A <at> 12V, 7A <at>12V/24V,
2A <at> 6V/12V/24V outputs
• 230(H) x 170(W) x 140(D)mm
Allows two batteries to be charged from
your engine alternator at the same time.
Emergency override feature. LED status
indicator.
• 67(L) x 67(W) x 53(H)mm
12V LEAD ACID
BATTERY TESTER QP-2261
250 LUMEN
WORKLIGHT ST-3273
Tests most automotive cranking lead
acid batteries, including an ordinary
lead acid battery, AGM flat plate,
AGM spiral, and GEL batteries.
• 6-30VDC voltage range
• 125(L) x 70(W) x 25(H)mm
$
84 95
Ultra compact, ideal for notebook
computers being moved around and where
a larger dongle may be easily knocked and
damaged. Dual band 2.4GHz and 5GHz.
USB2.0 AC600 YN-8334 $39.95
USB3.0 AC1300 YN-8336 $69.95
FROM
169
Rugged, holds a high
power 3W COB LED
with magnetic base for
convenient mounting.
Torch function.
PANASONIC CORDLESS PHONES
129
$
VDSL2/ADSL2+ WIRELESS
MODEM ROUTER YN-8345
NBN-ready device. Equipped with a
Gigabit Ethernet WAN port to provide
an instant connection to a Fibre / NBN
/ UFB service when available. Multiple
high speed Wi-Fi connections.
14 95
NOW
29 95
$
SAVE $20
BUNDLE DEAL INCLUDES ALARM AND:
1 X DOOR/WINDOW SWITCH
LA-5616 $29.95
1 X KEY FOB REMOTE
ALARM +
ACCESSORIES
LA-5618 $29.95
$
1 X MOTION SENSOR
LA-5614 $39.95
AR-1956 ORRP $49.95
Turn your smartphone into a remote control.
Organize all devices in your home via your
smart phone and make it a remote control.
• Includes voice control
WITH NFC AA-2108
Streams music from your Bluetooth®
or NFC® enabled device to your stereo
system. Easy to setup and can be
controlled from up to 10m away.
• 58(L) x 58(W) x 15(H)mm
348
SAVE $50
See website for more details.
$
99
179
$
720P WI-FI IP CAMERA QC-3835
Page 52
54 95
WIRELESS AUDIO RECEIVER
KLIKR SMARTPHONE
CONTROLLED IR REMOTE
299
View live footage on your Smartphone with
this high quality and easy to set-up camera.
Download free App to quickly configure and
monitor up to 15 cameras. Record videos to
microSD card (available separately).
• Motion detection
• Infrared LEDs for night vision
• 2-way audio
WITH BLUETOOTH®
Includes direct link to mobile, call block
and do not disturb modes, app alerts, full
speakerphone conferencing functions plus
an answering machine.
1 CORDED & 1 CORDLESS HANDSET
YT-9014 $169
1 CORDED & 2 CORDLESS HANDSETS
YT9016 $199
HOME THEATRE
$
SMARTPHONE CONTROL LA-5610
Control it via touchscreen, wireless key
fob remote or your Smartphone over your
wireless network. Features SMS, email
or auto-dial feature. 8 zones. Kit includes
motion sensor, 2 x door/window sensors,
key fob remote, batteries and power
supply. Easy to install and use.
Dual-Band
$
$
WI-FI ALARM SYSTEM WITH
99
SAVE $20
See website for contents.
SECURITY
$
NOW
$
STEREO
AMPLIFIER WALLPLATE AA-0519
119
$
Replace that bulky amplifier powering your
ceiling speakers with this clever wallplate.
Stream music from your Smartphone or
connect audio to the AUX input. Includes
12V mains adaptor.
• 2 x 15WRMS (4Ω) Class-D amplifier
Follow us at facebook.com/jaycarelectronics
CAT5/TCP/IP HDMI EXTENDER
AC-1734
Easily extend your HDMI source to a
display up to 100m away using CAT5E/6
cable. Suits common router or switch. IR
extender. 1080p.
ALSO AVAILABLE:
SPARE TCP/IP HDMI RECEIVER
AC-1735 $99.95
Catalogue Sale 24 November - 26 December, 2017
TECH TIP:
SINGLE BOARD COMPUTERS
With the advances allowing shrinking of technology, we can now fit a computer
onto a single printed circuit board- the single board computer. There are many
flavours of single board computers, from microcontrollers that are good for a
single dedicated task, through to the Raspberry Pi and PCDuino which can run
full multi-tasking operating systems.
An Arduino® UNO is a microcontroller single board computer, and it’s actually
comparable in processing power to the computer on Apollo 11. Arduino®'s are
great for doing a single task, such as reading a sensor and displaying it. Because
they are so simple, they are also a great way to learn programming, and are easy
to connect to real world hardware.
A Raspberry Pi, on the other hand, is comparable to a Pentium based computer,
and can run a full graphical desktop with apps like browsers and video players.
From replacing an old computer to constructing a home surveillance system, the
Raspberry Pi allows you to do more complex things than an Arduino®, especially
if it involves data intensive operations like video, audio or connecting to the
internet.
The PCDuino is similar to the Raspberry Pi in processing power, but adds the
real world accessibility of the Arduino® by incorporating an Arduino® compatible
pinout. Like the Raspberry Pi, the PCDuino also features HDMI, USB and Ethernet
to connect with common peripherals.
SEE OUR ARDUINO® PROJECTS:
www.jaycar.com.au/arduino
BEGINNER
DUINOTECH
CLASSIC (UNO)
XC-4410
The Duinotech Classic
is a 100% Arduino®
compatible
development board. Its
stackable design makes
adding expansion shields a
piece of cake. Powered from 7-12VDC or from
your computers USB port
• ATMega328P Microcontroller
19 95
$
SOLDERLESS BREADBOARD
$
29 95
INTERMEDIATE
WITH POWER SUPPLY PB-8819
830 tie-point breadboard with removable
power supply module. Includes 64 mixed
jumper wires of different length and colour.
• 3V and 5V switchable output
9 ea
$ 95
19 95
$
2 X 16 LCD CONTROLLER SHIELD
XC-4454
Allows you to create a user friendly
interface for your project. Comes with a
built-in 16 character by 2 line LCD display
with backlight. Six push button keypad.
$
FROM
99 95
RASPBERRY PI 3B
SINGLE BOARD COMPUTER
XC-9000
Quad-Core 1.2GHz CPU. 1GB
RAM. Wi-Fi and Bluetooth.
It can run Raspbian or
Ubuntu (varieties
of Linux) or even
Windows 10 IoT
core. Use it as
a media player or
even use the GPIO
ports to interact with real
world electronics.
• 4 USB ports
• HDMI
• Wi-Fi and Bluetooth®
ENCLOSURES FOR RASPBERRY PI
$
SEE PAGE 8 FOR MORE ACCESSORIES
74 95
Perfect for protecting your Pi. Includes
openings for the USB, HDMI, Ethernet,
3.5mm, MicroUSB and MicroSD card
and cooling holes. 2 colours.
BASIC BLACK XC-9002
CLEAR ACRYLIC XC-9004
TOUCHSCREENS WITH HDMI
AND USB FOR RASPBERRY PI XC-9024
Compact, portable display to connect
directly to your Pi. HDMI input and includes
a touch interface.
5" XC-9024 $99.95
7" XC-9026 $159
ADVANCED
PCDUINO V3.0
WITH WI-FI XC-4350
A high performance
mini PC platform that
runs on Ubuntu or
Android ICS. Features
onboard HDMI, USB,
SATA, LVDS and Wi-Fi.
• Supported digital
audio via I2C
• 121(L) x 65(W)
x 15(H)mm
SEE WEBSITE FOR MORE DETAILS: www.jaycar.com.au/pcduino
To order phone 1800 022 888 or visit www.jaycar.com.au
19 95
$
BLACK ENCLOSURE
$
89 95
XC-4354
House your PcDuino in this enclosure for a
safe and presentable appearance.
• Suits XC-4350
See terms & conditions on page 8.
$
89 95
7" LCD TOUCH SCREEN
MONITOR XC-4356
• 1024 x 600 resolution
• LVDS screen with driver board
• 167(L) x 107(W) x 10(D)mm
Page 53
WORKBENCH
ESSENTIALS
4
There has been an obvious resurgence in people getting back to the
workbench and reviving skills involving manual dexterity. As you will
see across the following pages, Jaycar has all the DIY tools you'll
need to equip your workbench so you can create projects from the
power of your brain and your hands.
NOW
159
$
SAVE $20
$
64
95
6
3
2. 5 PORT USB CHARGING STATION
WC-7766 WAS $69.95
• Charge up to 5 Tablets or Smartphones
• Max power output 2.4A per port
• Total output 8.2A
• Includes 12VDC & 4A power supply
NOW
179
$
1. TRUE RMS MULTIMETER QM-1321
• Non-contact voltage detection
• Autoranging
• CATIII 1000VDC
• AC/DC Current
SAVE $20
Accessories not included.
1
$
39
2
5
$
199
95
$
NOW
59 95
3. 2MP WI-FI DIGITAL MICROSCOPE
QC-3752 WAS $199
• 10x - 200x magnification
• LED backlit stand
• USB interface for connection with PC
• Rechargeable battery
SAVE $10
4. 0-30VDC 0-5A REGULATED POWER
SUPPLY MP-3840 WAS $179
• Digital control & easy to read LED display
• Built-in over-current & short circuit
protection
• 270(L) x 120(W) x 185(H)mm
5. 20MHZ USB OSCILLOSCOPE QC-1929
• Ultra portable
• USB interface plug & play
• Automatic setup
• Waveforms can be exported as Excel or
Word files
• Spectrum analyser (FFT)
• Includes 2 probes
6. MAGNIFYING LED LAMP QM-3544
• Great for arts and crafts, including model
making
• 3x & 12x magnifying lenses
• Ultra bright LED lamp
• Mains powered
TECHY GIFTS FOR THE MODEL BUILDERS
$
69 95
PLASTIC WELDING KIT TS-1331
$
54 95
Save money and repair small/medium cracks
with this cordless welding kit.
• Cordless gas-powered welder
ROTARY TOOL KIT TD-2459
• Fast heating process
Drill, saw, sand, polish, carve or grind.
210 piece with flexible shaft.
• 4 plastic filler types included
$
24 95
14 95
$
MICRO ENGRAVER TD-2468
Engraves glass, ceramics, metals and
plastics for security or insurance.
• Spins at 10,000 RPM
FILE KIT TD-2128
All have integrated plastic handles and come
in a handy storage wallet. 10 piece.
• 162mm long each
TECHY TOOLS FOR YOUR CHRISTMAS PROJECT
400A AC/DC CLAMP
METER QM-1563
Easy one-hand operation
perfect for the working
installer or tradesman.
600V, 4000 count. 400A
AC/DC. Includes test leads
& temperature probe.
• Autoranging
• 30mm jaw opening
• 200(H) x 66(W) x 37(D)mm
$
99 95
$
48W SOLDERING STATION TS-1564
Adjustable temperature (150-450°C), ceramic
element and a lightweight pencil for fatiguefree soldering.
• Mains powered
• 150(L) x 115(W) x 92(H)mm
129
$
Page 54
39 95
$
LCD TYPE CALIPER TD-2082
Stainless steel. 5 digit LCD display. 150mm
range. Supplied with a sturdy clip-lock case.
ALSO AVAILABLE:
BUDGET 150MM DIGITAL VERNIER
CALIPERS TD-2081 $13.95
Follow us at facebook.com/jaycarelectronics
29 95
GAMING
CONSOLE
TOOL KIT TD-2109
Includes tools for nearly every console and
handheld on the market today - WII, X-Box,
Playstation etc.
Catalogue Sale 24 November - 26 December, 2017
EXCLUSIVE
CLUB OFFERS:
15% OFF
15% OFF
ALARM
F
F
O
15% SIRENS &
FOR NERD PERKS CLUB MEMBERS
WE HAVE SPECIAL OFFERS EVERY MONTH.
LOOK OUT FOR THESE TICKETS IN-STORE!
ALARM
STROBES
SIRENS &
M
ALAR
STROBES
RENS &
SIEXCLUSIVE
CLUB
OFFER
S
BE
STRO EXCLUSIV
NOT A MEMBER? Visit www.jaycar.com.au/nerdperks
NERD PERKS CLUB OFFER
E
CLUB OFFE
NERD PERKS CLUB
OFFER
R
SAVE 20%
SAVE 30%
GAMER
BUNDLE
INCLUDES:
USB GAMING KEYBOARD
XC-5130 $29.95
USB GAMING MOUSE
XM-5250 $32.95
$
Sign up NOW! It’s free to join.
E
EXCLUSIV
CLUB OFFER
NOT
A MEMValid 24/7/17 to 23/8/17
Sign up NOW BER?
! It’s free to
join.
Valid 24/7/17 to
BER?
NOT A MEM! It’s free to join.
NERD PERKS CLUB OFFER
20% OFF
23/8/17
Sign up NOW
Valid 24/7/17 to
23/8/17
30M ALARM CABLES*
NETWORK
CABLE
TRACER
ONLY
VALUED AT $62.90
NOT A MEMBER?
50
XC-5083
WAS $99.95
SAVE $30
NOW ONLY
$
69 95
*Applies to WB-1591 & WB-1596.
NERD PERKS
NERD PERKS
NERD PERKS
NERD PERKS
SAVE
SAVE
SAVE
SAVE
20%
30%
12VDC RELAY CARD KIT
DOUBLE GPO
KG-9142 REG $12.95 CLUB $9.95
5mA 3A.
PS-4065 REG $29.95 CLUB $19.95
With 2 x USB Charging ports.
20%
NON-CONTACT
AC VOLTAGE DETECTOR
NERD PERKS
NERD PERKS
SAVE
SAVE
SAVE
10%
200 PIECE SPRING ASSORTMENT F-TYPE LTE FILTER
HP-0638 REG $19.95 CLUB $14.95
Supplied in a plastic case.
LT-3067 REG $19.95 CLUB $17.95
FL694LP 4G.
NERD PERKS
HALF
PRICE!
SAVE
ZW-3100 REG $13.95 CLUB $9.95
NA-1004 REG $11.50 CLUB $5.75
NERD PERKS CLUB MEMBERS RECEIVE:
STORAGE CASE
HB-6305 REG $18.95 CLUB $15.95
19 compartment.
NERD PERKS
SAVE
20%
10%
AUTOMOTIVE FUSE BOX
7 CORE TRAILER CABLE
SZ-2002 REG $12.95 CLUB $9.95
6 way.
WH-3090 REG $44.95 CLUB $39.95
10m length.
15%
OFF
ALARM SIRENS & STROBES
To order phone 1800 022 888 or visit www.jaycar.com.au
SAVE
15%
RC-5496 REG $9.95 CLUB $7.95
0.1uF 50V Blue chip.
NERD PERKS
ELECTRONIC CLEANING
SOLVENT 175G
NERD PERKS
MONOLYTHIC
CAPACITOR PK.100
SAVE
WIRELESS 433MHZ
TRANSMITTER MODULE
HB-5062 REG $9.95 CLUB $7.95
111 x 60 x 30mm.
20%
NERD PERKS
25%
DIE-CAST ALUMINIUM BOX
QP-2268 REG $24.95 CLUB $19.95
Detects voltages from 50 - 1000V.
NERD PERKS
25%
20%
YOUR CLUB, YOUR PERKS:
REMEMBER TO GET YOUR CARD SCANNED AT
THE COUNTER TO GET POINTS*.
$1 = 1 POINT,
500 POINTS = $25 JAYCOINS GIFT CARD
See terms & conditions on page 8.
Conditions apply. See website for T&Cs
*
Page 55
WHAT'S NEW
WE'VE HAND PICKED JUST SOME OF OUR LATEST NEW PRODUCTS. ENJOY!
LONG RANGE LORA
IP GATEWAY XC-4394
LoRa is the latest technology being used by Arduino®
devices for powerful connectivity with 3G/4G
access (USB 3G/4G dongle required), or
via the WAN port. Faster and better,
highly customisable using the
open source OpenWrt system.
• LoRa and Wi-Fi connectivity
• Cloud-based remote
management
• Detachable high-gain antenna
149
$
$
ACCESSORIES FOR YOUR PI
89 95
MINI WIRELESS ALARM KIT LA-5282
No messy cables to run! Wireless connection
of all compoents. Quick and easy installation.
Easily expanded to cover a greater area.
• Super-loud 120dB siren
$
$
24 95
$
59 95
2.8" TOUCHSCREEN XC-9022
Connects directly to the Pi. Capable of up
to 2592x1944 resolution. Supports video
recording for 1080p <at> 30fps, 720p <at> 60fps
and 640x480p <at> 60/90fps.
• 25(W) x 20(L) x 9(H)mm
A compact fully featured 16 bit 320x240
pixel 2.8 inch resistive touch display.
Low power requirement, powered
directly from the GPIO pins.
DUMMY BULLET
CAMERA LA-5338
Realistic dummy surveillance
camera to deter thieves.
Includes a CCTV warning
sticker.
299
RF OVER CAT5 AMPLIFIER LT-3236
5MP CAMERA XC-9020
14 95
$
Capable of supplying quality signal to up
to four televison receivers. High output.
Wide bandwidth.
• 35dB maximum gain
• -20dB test point
2M LEAD TO SUIT LT-3237 $29.95
$
89 95
QUICK CHARGE™ 3.0
POWER BANK MB-3725
Huge 10,000mAh Li-Po battery supports
powering and recharging your devices
using latest Qualcomm® Quick Charge™
3.0 technology. Recharge the unit via USB
Type-C or micro USB.
MODIFIED SINEWAVE INVERTERS
15 95
12 95
$
$
PROTOTYPING HAT XC-9040
Includes screw terminals and solder
points for the GPIO pins.
• 85(W) x 56(L)mm
GPIO EXPANSION KIT XC-9042
Makes Raspberry Pi prototyping much
simpler.
WITH USB AND LCD DISPLAY
Power handheld power tools, televisions, gaming consoles,
home electronics and small appliances in your car,
truck, boat or RV. 12VDC to 230VAC.
Short circuit / overload protection.
• Dual USB port
• Remote control
• Thermal fan
1100W MI-5140 $279
1500W MI-5142 $399
2000W MI-5144 $549
FROM
$
279
TERMS AND CONDITIONS: REWARDS / NERD PERKS CARD HOLDERS FREE GIFT, % SAVING DEALS, DOUBLE POINTS & MEMBERS OFFERS requires ACTIVE Jaycar Rewards / Nerd Perks Card membership at time of purchase. Refer to website for Rewards/Nerd Perks
Card T&Cs. PAGE 3: Nerd Perks Card holders receive special price of $69.95 for Singing LED Christmas Tree Project Kit (1 x XC-4410 + 1 x XC-4536 + 3 x XC-4380 + 1 x AB-3440 + 1 x XC-4983) when purchased as bundle. PAGE 5: Wi-Fi Alarm System BUNDLE DEAL includes
1 x LA-5610, 1 x LA-5616, 1 x LA-5618 & 1 x LA-5614. PAGE 7: Nerd Perks Card holders receive 20% OFF 30m Alarm Cables applies to WB-1591 & WB-1596. Gamer Bundle for $50 includes 1 x XC-5130 & 1 x XM-5250 when purchased as bundle. Nerd Perks Card holders
receive 15% OFF Alarm Sirens & Strobes applies to Jaycar 620E Alarm Sensor, Sirens & Strobe product category.
BORANUP
AVE
CALO
UN
RD DRA
LOW
ER K
E
KEY LARGO DR
THE STRAITS
YS D
R
NEERA
BUP R
D
BUNN
INGS
NEW STORE: CLARKSON
12A/61 Key Largo Drive Clarkson, 6030 WA
(Enter via Lower Keys Dr - opposite Bunnings)
PH: (08) 6202 0131
FOR YOUR NEAREST STORE &
OPENING HOURS:
1800 022 888
www.jaycar.com.au
93 STORES & OVER
140 STOCKISTS NATIONWIDE
Head Office
320 Victoria Road,
Rydalmere NSW 2116
Ph: (02) 8832 3100
Fax: (02) 8832 3169
Online Orders
www.jaycar.com.au
techstore<at>jaycar.com.au
Arrival dates of new products in this flyer were confirmed at the time of print but delays sometimes occur. Please ring your local store to check
stock details. Occasionally there are discontinued items advertised on a special / lower price in this promotional flyer that has limited to nil stock
in certain stores, including Jaycar Authorised Stockist. These stores may not have stock of these items and can not order or transfer stock.
Savings off Original RRP. Prices and special offers are valid from Catalogue Sale 24 November - 26 December, 2017.
It is a long time since SILICON CHIP
reviewed a turntable – almost 20
years, in fact. Since then, vinyl
records and turntables had
experienced a long decline . . .
but more recently quite a strong revival,
with many groups and musicians releasing
new vinyl recordings. To meet this new demand,
a number of new turntables have appeared on the
market, including the Music Hall mmf-1.3 reviewed here.
Review by Leo Simpson
T
he mmf-1.3 is a 3-speed belt-driven manual turntable fitted with an Audio-Technica AT-3600L moving
magnet cartridge and an inbuilt RIAA preamplifier,
providing line-level signals which can be fed to any modern sound system.
If you have a stereo amplifier or surround-sound receiver with its own RIAA preamplifier, you have the option of
switching the turntable’s outputs to the unequalised (ie,
no RIAA equalisation or preamplification).
And while the turntable is belt-driven, it is powered by
an electronically-controlled low voltage motor; probably
a crystal-controlled brushless DC motor (often described
as a DC servo motor) which provides speeds of 33.33, 45
siliconchip.com.au
and 78 RPM. This is a more elegant approach than used
in most belt-driven turntables of the past which typically
had a mains-power synchronous motor driving a stepped
pulley to provide, usually, just two speeds.
There are several benefits in using the low voltage electronically-controlled motor. One of these is that the Music
Hall turntable can be used virtually anywhere that 12V DC
is available (OK, perhaps not in a car or on a boat!). It is
not affected by the mains frequency (ie, 50Hz or 60Hz) as
it uses a 12V DC plugpack.
And since it does not use a synchronous motor locked
to the local mains frequency, the turntable’s speed can be
set to the exact value.
Celebrating 30 Years
December 2017 57
Here’s the adjustment end of the tone arm, with the tracking
dial at the rear and the anti-skate control closest to the
camera. The tone arm is raised and lowered by the lever in
the foreground.
The belt drive fits right around the turntable inner rim
thence to the capstan, seen here in its access window. You
have to remove the platter mat to gain access to this window
but fitting the belt is neither difficult nor time consuming.
The presentation of the Music Hall turntable is very clean
and simple: a shallow glossy back plinth supported on four
large vibration-damping feet and fitted with a removable,
moulded clear Perspex dust cover. Lifting the cover gives
access to the 4-position switch which turns on the power
and selects the three speeds: 33.33, 45 or 78 RPM.
The tonearm is a straight (not curved) design with a removeable EIAJ headshell and adjustable counterweight
which allows the tracking force to be set between one and
four grams (once it has been balanced). There is also an
anti-skating force adjustment.
Note that since this is a manual turntable, moving the
arm off the rest does not start the platter revolving – that
is done by the speed selector/power switch. And nor does
the platter stop revolving once the stylus runs into the
central groove.
So the playing procedure is to start the turntable, position the stylus over the run-in groove and then flick the
damped lift/lower level to gently lower the cartridge into
the groove. At the end of play, you use the lever to raise
the tonearm and then you move it back to the rest position.
This is simplicity itself and the way most record enthusiasts like it.
The Audio-Technica AT-3600L moving magnet cartridge
is a middle-of-the-road model with a 0.6 mil conical stylus
and a recommended tracking force of 3.5 grams. It does have
a removeable stylus (AT-91R) so it can be replaced at some
time in the future (after you have played a lot of records!)
By the way, the AT-3600L cartridge is not suitable for
playing 78 RPM records. This will not affect most people
since 78 RPM discs are quite rare – but if you did want to
play them, to get the best results, you will need a cartridge
with larger stylus, typically 3 mil.
The much smaller stylus of any cartridge intended for
microgroove (ie, 33 and 45 RPM) records will ride in the
bottom of the groove of 78 RPM records and be very noisy.
In that case it is best to go for a dedicated 78 RPM mono
cartridge such as the Audio-Technica VM670SP.
The turntable itself is a lightweight aluminium casting
which has a thick rubber mat. Total weight of the platter
and rubber mat is 785g.
We like the inbuilt preamplifier on the Music Hall turntable as it means its output leads can be plugged into any
amplifier which can accept line level inputs, ie, with signal levels up to 1 or 2V.
On upacking the mmf-1.3 turntable, we checked the speed
of the turntable with the SILICON CHIP strobe disc and white
LED strobe (December 2015) and found it was spot on at all
speeds, straight out of the box. . .
. . . but if it proved to be slightly “out”, it’s a simple matter
of adjusting the speed by holding down the push button
for two seconds then turning the knob. Unfortunately, it is
under the turntable so takes a bit of juggling to get to!
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Silicon Chip
Setting up
The mmf.1.3 turntable requires very little assembly out
of the box. The main task is to install the platter on the
spindle and make sure the belt is sitting on the motor shaft.
Celebrating 30 Years
siliconchip.com.au
The mmf-1.3 is a fully manual turntable, which means
it doesn’t start operating when you lift the tone arm.
The motor is controlled via the speed selection knob.
Unusually, this turntable offers a 78RPM speed.
The rear panel sports the 12V DC input socket (plugpack
supplied), a “GND” terminal and stereo RCA output
sockets. You can choose RIAA line-level or “straight”
phono output via the switch alongside the output sockets.
But anyone using a turntable for the first time would be
wise to check that the tonearm is correctly balanced and
that the tracking and anti-skating settings are correct. The
instruction manual is quite good in this respect but anyone
who has never set up a turntable would probably be wise
to ask their audio retailer how it is done or have a look at
video on the internet.
RCA leads are supplied so it is simply a matter of connecting these to the line inputs on your amplifier and you
are ready to play. Before we did that, we checked the speeds
of 33.33, 45 and 78 RPM using our 100Hz white LED strobe
and strobe disc.
This showed that the speed settings were exact, with
no drift of the disc strobe markings on any speed setting
(see SILICON CHIP, December 2015: siliconchip.com.au/
Article/9640).
If the speeds had been slightly off, the turntable has a facility for slightly increasing or decreasing the speed. This
is a small pushbutton and knob on the underside of the
turntable, at the lefthand side.
To change a speed setting, you first select the speed, then
press and hold the button for two seconds and a LED comes
on, You can then turn the knob to increase or decrease the
speed to the desired setting. After that, you press the button again, the LED will flash and then turn off and the new
speed setting will be stored by the unit’s microprocessor.
We then set up the arm for balance, set the tracking for
3.5 grams and adjusted the anti-skating force accordingly,
prior to testing the tracking ability of the cartridge using a
variety of test records, some of which provide very stringent testing. In summary, the supplied Audio-Technica cartridge is adequate for average listening but records with very
high recording levels will cause it to seriously mistrack.
By the way, we regard 3.5 grams as a fairly high tracking force – we tried it at 2 grams and found that this made
little difference in tracking performance.
Our next series of tests involved frequency response
and we were able to confirm that the fitted Audio-Technica 3600L cartridge has a response within ±2dB from 20Hz
to 20kHz. Channel balance is within 1.5dB and channel
separation averages between -15 and -20dB. The waveform
on sinewaves is good. These tests were performed with the
CBS STR100 test record.
Wow & flutter was quite low and difficult to measure,
as was rumble. We would expect that result with this beltdrive/electronically controlled motor system.
And then it was on to playing records. This was the most
enjoyable part of this review, being satisfied that the Music
Hall turntable and cartridge performs well. The Audio-Technica has a clean, bright sound which does not emphasise
surface noise and clicks – most important if you are playing older records which will inevitably have their share.
You can buy it with confidence.
The Music Hall mmf-1.3 turntable has a recommended
retail price of $499 inc GST.
For further information, contact the Australian distributors, Convoy International Pty Ltd, Phone (02) 9774 9900;
SC
website www.convoy.com.au
The mmf-1.3 is supplied with an Audio-Technica AT-3600L
moving magnet cartridge, a middle-of-the-road model with a
0.6 mil conical stylus and a recommended tracking force of
3.5 grams. Note that this stylus will not play 78RPM records!
The hinged perspex lid on the mmf-1.3 turntable is
completely removable, for those who prefer to operate that
way (or to house the turntable in a hifi unit, for example).
Size (without lid) is 435mm W x 106mm H x 367mm D.
siliconchip.com.au
Celebrating 30 Years
December 2017 59
SERVICEMAN'S LOG
Video trials and tribulations
Dave Thompson*
What did we do before USB flash drives became available. They certainly
simplify the playback of digital content but even though they are not
mechanical, I have found some unexpected reliability problems. We have
become so used to the innate reliability of electronics equipment and
it now it seem that can no longer be taken for granted. Still, if you are
prepared to delve into these problems, the repairs can be quite simple.
Long-time readers of this column
may recall the trials and tribulations
I experienced when we purchased a
new home-theatre system a few years
back.
My main gripe was with disc region
codes; after years of playing discs from
all regions in our old, all-zones player, this new Blu-ray capable system
would only play Zone 4 discs.
For those unfamiliar, powerful entertainment-industry lobbyists forced
major manufacturers to implement a
region coding system for DVDs, which
meant, for example, discs produced for
the American market wouldn’t play
on a system designed for the
Australasian market.
This was apparently done to protect
the industry from loss of income due
to them not having control of when
and where movies are released.
But what it really does is impose
price-fixing and monopolising practices onto consumers, which is why
there is barely any legal basis for disc
zoning in most countries.
Thankfully, some manufacturers
ignored these directives and consequently most of us had relatively easy
access to region-free DVD players, at
least we did until Blu-ray came along.
Once again, consumers on this side
of the world are forced to buy inflatedpriced discs long after northern-hemisphere buyers get
to enjoy them, while they
also have a larger variety
of titles at subsidisedby-us prices.
Some good news
is that there is a
huge, quasi-underground network
of dedicated reverse-engineer
types working
to provide
region-free firmware for all brands of
consumer disc players.
Except that back then, there was no
firmware available for our particular
player, and while there might be something now, we’ve long-since worked
around the issue.
For starters, we don’t play Blu-ray
discs, and most of the material we
watch is digital content stored on
USB media, so it isn’t such a big deal
any more.
The biggest blow back then was the
fact we couldn’t play any of the dozens of European (Zone 2) discs we’d
picked up on our travels, including
many titles that were never released
on DVD in this region.
How these corporate bullies still
get away with dictating what we can
watch and when (if at all) escapes me,
which is why I enjoy undermining
their efforts to beat me down. Note that
I’m not advocating ripping off studios
or creators, I’m talking only about legally-acquired media.
When I discovered this LG system
was region-locked, I very nearly returned it and likely would have, until I learned there were no region-free
Blu-ray home-theatre systems on the
market here yet to swap it with. Such
is technological progress.
USB is the answer
This means the main way we watch
content on our system these days is
via a USB flash drive. The system is
network capable, and “internet ready”
but the proprietary WiFi dongle it requires is so ridiculously overpriced I
refuse to buy it.
Running a permanent cable is not
feasible either, given the location of
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Celebrating 30 Years
siliconchip.com.au
Items Covered This Month
•
•
•
Blu-ray player and HandyCam
360° passive infrared sensor
repair
Fuse blows, stove goes
*Dave Thompson runs PC Anytime
in Christchurch, NZ.
Website: www.pcanytime.co.nz
Email: dave<at>pcanytime.co.nz
the system and the distance from the
nearest network switch.
It’s not really a bother; we simply
load up what we want to watch on a
flash drive and put it into the single
USB port in the front of the player;
after a few seconds we have a basic
file-system we can surf around using
the remote and choose the file to play.
However, of late, we’ve had a few
problems with the drives. Initially, I
thought we might have worn out one
of them, as it would "drop out" once or
twice and we’d have to re-insert it and
fiddle about to try and find where we
left off. This was annoying but with it
only happening every now and then,
not a show-stopper.
Eventually I bought a couple of
higher-capacity flash drives and was
mildly peeved to find one sporadically
not being recognised by the system.
Eventually, it got to the point where
none of the drives would register until we plugged and re-plugged the
drive and even then only with
significant wiggling around;
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obviously there was something amiss.
Like all servicemen, I’m always
ready to drop everything and head to
the workshop. This particular night
we were hyped to watch a particularly
good show and the air was rendered
blue when we discovered that none of
the flash drives would "play".
After unplugging the raft of cables
and plugs connecting the base unit
to the speakers and peripherals, I repaired to the workshop to do some,
er, repairs.
Opening the thing up was simplicity itself. Six small screws held the
metal "top-hat" style metal case onto
the base. The shape of the cover required me to splay the bottom edges
out to lift it straight up and away to
reveal the interior.
The USB socket was in plain sight,
though due to the way it was situated,
the soldered connections were underneath the board. So another half a dozen screws needed to be removed and
a few flying leads and plugs removed
before I could flip the PCB over.
Immediately I could see the problem: every one of the socket’s four
solder joints had a tell-tale dark ring
around the lead coming through the
board. Flexing the socket widened
these rings on one side and compressed them on the other, indicating
that all were fractured and would only
electrically connect when the socket
was pressured this way or that.
No wonder the programs were dropping out and it was hard to get the
drive initialised in the first
place. In fact, I was surprised it worked at all,
given the gaps in the
solder joints.
By this time my
soldering station
was well up to
temp and a quick
application of heat
and a press of the
button on my Goot
solder sucker soon
had each pad on
the PCB and the
socket’s leads
clear of old, dry
solder.
I sweated in
each joint with a
fresh pool of solder and flipped
the board over to
check it had gotten
Celebrating 30 Years
right through to the opposite side as
well. It all looked good and within 10
minutes the screws were back in and
I was in the lounge plugging all those
cables back in.
From that point to this, any flash
drive inserted registers almost instantly and is ready to go within seconds.
Interestingly, I never recalled it being
that good before, so perhaps it had
been defective right from the word go.
There was certainly very little solder on those connections and a lot
less that it has now. I guess this is the
price we pay for lower-cost electronics
in general but surely a bit more solder
all-‘round wouldn’t break the bank.
HandyCam challenge
Another challenge I faced recently
was with my Sony HandyCam. While
this is now about 10 years old, it is
still a pretty good little camera and
since I need a decent camera for my
new YouTube venture, it was, as the
Americans say, a "no-brainer" to dust it
off and charge it up, ready for testing.
Over the years, I’ve taken a lot of
video and stills with this camera. The
4-megapixel sensor might be a bit lame
compared to what’s available now but
back then it was the business.
However, since in all those years I’d
never dumped many of the photos or
videos I’d taken from the 40-gigabyte
hard disc, it was pretty full.
I recently recorded a couple of test
clips with it and while only HD rated
(720p), it will do me fine, until I can
afford to shell out for a mirrorless,
DSLR FHD camera that can do 1080p
at 60 frames a second. Best tools for
the job, right?
And therein lies my problem; the
display shows a mere 18 minutes of
hard-disc space remaining if I continued filming at the current resolution.
To do anything serious, I’d need to
December 2017 61
dump the data on the camera’s drive
to one of my computers to free up a
bit of space.
To accomplish this, Sony deemed
it necessary to provide just one way
of getting the files from the camera to
a computer. Actually, there were two,
possibly three ways, but I’ll talk about
that in a minute.
The problem was that in the shift
to this new house, I’ve misplaced the
supplied USB docking station the
camera requires for a computer connection.
A quick look on the local auction
sites didn’t show any of the correct
model for sale and according to references I found in forum posts regarding the subject, Sony have long-since
stopped making and selling them. I also
tried the usual Chinese online sources
but there was nothing there either.
Convinced the docking station must
be packed away in one of the dozens
of boxes we still hadn’t un-packed, I
spent an entire weekend opening and
sorting through so much extraneous
rubbish that I was almost ready to
dump it all straight into a skip.
I don’t consider myself a hoarder
and it isn’t like I have to sleep standing up because every square metre of
62
Silicon Chip
floor space is packed to the ceiling with
swag but I do appear to have a lot of
stuff I could well do without.
How I ever accumulated it all is a
mystery. I can’t recall buying a lot of it
but it’s there so I must have acquired
it at some stage! Annoyingly, though,
the docking station was nowhere to
be found.
It was time to get creative. I blew the
dust off my eBay account and hit the
international auction sites to try and
find one. The model I was after is the
DCRA-171, made especially for my
camera and a handful of other models. I found a couple, and was quite
excited until I saw they were asking
as much as US$95! That seemed a little steep, but I guess the price reflected just how hard to find these things
were becoming.
After a bit more digging, I found one
listed on the UK eBay site, for a much
more reasonable £12, roughly NZ$25.
I placed a bid after discovering they
shipped overseas and even with shipping included, I’d be looking at about
fifty bucks, still a bit high but realistically a much more reasonable amount.
The day of the auction came and
went; when checked I discovered it
had been purchased by someone else
Celebrating 30 Years
after a small bidding war for £35! This
was getting tiresome.
It was about this time I noticed the
camera also has a memory card slot. It
is tucked away under the fold-out LCD
screen and I’d never really noticed it
before. This could be the solution. If I
could still get a memory card to fit it,
perhaps I could transfer the files from
the camera’s hard disc to the flash media and transfer them to the computer using a card reader. That sounded
much more feasible.
I checked AliExpress and the MSDuo cards the camera took were as
cheap as, er, chips and it was no big
deal if I had to wait a little while for it.
However, before I committed myself, I checked the camera’s user manual and believe it or not, there is no way
to transfer files from the hard drive to
the memory card. I could do it the other way, from the flash drive to the hard
disc, but not the way I needed. Darnit!
However, while I was looking on
AliExpress, a camera caught my eye; it
was one of those "action cameras" with
all the cases, mounts and trimmings
for just US$45. Cheaper than a docking
station and with claims of 4K video at
25 frames per second, this seemed an
ideal solution to my problem.
The only extra hardware this camera required was a microSD card and
as I already had a couple on hand, I
wouldn’t need to buy anything else.
Sadly, I put the Sony back in the
drawer while I waited for this one to arrive. I had plenty else to do in the meantime so I went on with that instead.
The camera duly arrived and I was
impressed. It came with a clear, water-proof housing and a dozen other
adaptors and mounts for helmets, handlebars and tripods. I mounted it onto
my tripod and set about testing it out.
The first thing I discovered was that
when set to 4K recording, it could only
manage about one or two frames per
second; a long way away from the 25
FPS claimed. No real harm; I wouldn’t
record in 4K anyway, so it was moot.
However, after further trials, I discovered the camera could only manage a maximum of 23 FPS at 720p and
while truthfully I had no right to expect a 4K, 25 FPS capable camera for
that money, I still felt burned.
And then there is the audio quality;
the on-board mic level was poor and
while this was to be expected when
mounted inside the water-proof case,
even when sitting outside the case the
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audio capture wasn’t great. If I did use
the camera, the cover could be handy
as at times it would be working in a
dusty workshop environment.
As a potential workaround, I carefully bored a 2mm hole through the
plastic case adjacent to the mic aperture in the camera’s case – after all, it
wouldn’t be going under water. While
this improved things a bit, it wasn’t
enough to allow me to record without an external mic, which the camera doesn’t have facilities for anyway.
Boy, this YouTube stuff is difficult!
With that camera a dead duck, I
returned to the Sony and the web. I
eventually stumbled upon a schematic someone had drawn up depicting
the DCRA-171 docking station’s proprietary USB connections. This was
more like it; this might enable me to
solder a cable or connector directly
to the camera’s PCB.
Though heartened, I was reluctant
to pull the camera apart. I remembered last time I repaired it, how complex it was and this time I would need
to strip it down even further, right to
the bottom of the camera.
I took my time and after careful
parts removal, finally reached the
socket. To my dismay, the connector
markings bore no resemblance to the
diagram. Nothing tallied and the two
components seemed miles apart, with
nothing referencing the other.
There were no pin numbers visible and though I had a good go with
a multimeter, trying to ‘ring out’ the
ground, +5V and data + and - leads
and match anything at all to the diagram, it was to no avail. Annoyed, I
reassembled the camera, wondering
where to go from here.
Then, I got lucky. As if on cue, an
email notification popped up saying a keyword search I’d set up on a
local on-line auction site had a hit.
I immediately went online found a
guy selling a DCRA-171 docking station for $20 plus shipping; I bought
it on the spot.
It arrived a few days later and I
hoped like hell I’d not caused more
problems mucking around with the
socket. I needn’t have worried. The
USB connected straight away and I
cleared the files from the drive. Now:
lights, camera, action!
360° PIR Sensor Repair
When something breaks, usually the
worst case is that you have to replace
siliconchip.com.au
it with a new one. B. P., of Dundathu,
Qld did just that, only to find that not
only was the brand new unit broken
and would need to be fixed, it also had
to be modified to fit where the old one
had been mounted! Here is the story
as he tells it…
When we built our new house in
the early 1990s, I installed a 360° PIR
(passive infrared) sensor underneath
the front verandah, near the outside
edge, to operate two coach lights on
the front wall of the house (either side
of the front door) automatically whenever someone approached.
The sensor only worked for a short
time. I wondered why it had failed
when it was still nearly new, so I removed it and inspected it. I found that
the circuit consisted of a 270Ω 0.5W
resistor in series with an X2 capacitor, followed by a bridge rectifier, zener diode and electrolytic capacitor
to supply the low voltage to operate
the unit. This is the same arrangement
used in many low-power mains-connected devices.
It was the inrush current limiting
resistor that had burned out. Luckily,
the resistor had burned out in such a
way that I could still read the value.
I replaced the resistor with the same
type and as a precaution, I wrote its
value on the PCB, just in case it ever
needed replacing again. The unit then
worked again for a short time, before
failing yet again and it was the same
resistor that had burned out yet again.
I could see that this was going to
be an ongoing problem, so I decided
to replace the resistor with something
more substantial. I looked through my
stock and decided to use two 150Ω 1W
resistors in series, as that was the closest I could find at short notice. The total was 300Ω, but it should work OK.
Well, that was obviously the right
thing to do as the unit then worked
for over 20 years with no issues, until
one day when my wife said that it had
stopped again. I took the plastic cover
off and it promptly disintegrated in my
hand due to its old age. So clearly, I
needed to replace the whole thing, no
matter what was wrong with it.
A couple of days later, we were in
Bunnings so I headed to the electrical department and we soon spotted a
similar unit on the display wall. However, when we checked the shelf, there
were none in stock.
In a stroke of luck, the company rep
for that brand was in the store doing
Celebrating 30 Years
December 2017 63
a stock-take, so she grabbed a ladder
to scan the unit on the wall to check
the stock. On her way up the ladder,
she spotted a box at the back of the top
shelf, with the last remaining 360° PIR
sensor, so we bought it.
Later, when I went to fit it, I checked
the light switch for the old sensor and
it was off, so it's possible that the old
sensor was still in working order.
The problem had been that a storm
one night, some time back, kept tripping the sensor and turning on the
coach lights, which are near our bedroom, so it had been turned off and
we then forgot to turn it back on later.
Note to self: next time, check that
the unit is switched on before taking
it apart to fix it!
Anyway, I got set to fit the new sensor and the first problem was that I
needed to drill new holes in the Villaboard ceiling because the new sensor had a different mounting arrangement to the old one. I screwed the base
to the ceiling with the idea being that
the PIR sensor itself would then clip
into the base.
But when I grabbed the unit itself,
I could see that there was a problem
because the three-wire terminal block
protruded and would foul the ceiling.
That would mean I would have to
drill a large clearance hole in the Villaboard, which I did not want to do.
I can’t say I was very impressed with
the design at that stage.
However, I was able to cut the terminal block into three individual terminals with a Stanley Knife so that the
terminals could lie flat and therefore
fit in the recess in the back of the unit.
Problem solved.
As I proceeded with the installation,
I thought I would set the three adjustments: LUX (light threshold), SENS
(movement sensitivity) and TIME
(light on-time) to the values I wanted.
I set SENS to maximum and LUX to
a daylight level so I could test the unit
after installation. But when I went to
set the time to the minimum, the small
adjusting knob kept turning and did
not stop.
Something was obviously wrong
there, so I took the unit down and
opened it up. The two sections of the
case are held together by four clips
around the edge of the unit, so I was
able to separate them without too
much trouble.
A closer look revealed that someone
had tried to adjust this unit on a previous occasion and turned the adjuster
hard against the stop and broken off
the small square plastic extension of
the knob that sits inside the pre-set pot.
What to do? I could not take the unit
back for exchange because it was the
only one in stock and besides that,
I had already modified the terminal
block. There were three choices: bin
the unit, put it up with the broken part
or try to repair it. I quickly ruled out
the first two, so I had to work out a
way to repair this small plastic knob.
I needed to think of something to
add a new square extension to it, in
order to restore it. I tried to think of
something of the right size with a
square cross-section to replace the
broken piece of plastic with and then
I realised a matchstick would do the
job. I cut the head off a match and compared it to the broken piece; it was an
almost perfect match.
So I removed the knob and very carefully drilled a hole where the stop had
broken off, using my cordless drill at
minimum speed, while holding the
knob in my fingers. I started with a
1/16-inch drill, then a 5/64-inch drill,
then a 3/32-inch drill. The resulting
hole was a tight fit for the matchstick
shaft, so I glued it into the hole using
a drop of super glue.
I then trimmed the match to length
carefully with a fine-tooth hacksaw
blade and reassembled the unit. This
somewhat unusual repair resulted in
the restoration of the sensor to “good
as new” condition and saved it from
the bin. Unfortunately, these days,
things are not made to be repaired,
so you often have to be crafty when it
comes to repairs.
I was then able to adjust the delay
time to just above the minimum set-
Servicing Stories Wanted
Do you have any good servicing stories that you would like to share in The Serviceman
column? If so, why not send those stories in to us?
We pay for all contributions published but please note that your material must
be original. Send your contribution by email to: editor<at>siliconchip.com.au
Please be sure to include your full name and address details.
64
Silicon Chip
Celebrating 30 Years
ting and soon had the unit mounted in
place. Job done. I turned the power and
light switch back on and went outside.
The lights were on, but they stayed on
for over a minute, so I started thinking
that maybe there was a fault with the
unit. Then the lights went out.
That was a relief as it just meant that
the TIME adjustment was set too high.
I set it to the minimum and stepped
aside. The lights stayed on for eight
seconds, so that was too short. I advanced the setting small amount and
this resulted in a 15-second delay before the lights went off.
I was aiming for 20 seconds, so I adjusted the setting by a hair and stood
aside. The lights then stayed on for
well over a minute, which was far
too long.
I set the adjustment back by a hair
and this resulted in a 15-second delay
again. This adjustment was far too sensitive, so I just settled for the 15-second delay. I then set the LUX setting
to a suitable level for night-only activation and the job was done.
Exploding circuit board
in my stove!
R. B., of Kambah, ACT was cooking
a stir fry when his induction cook-top
abruptly gave up the ghost. Luckily,
the repair was reasonably straightforward and economical, considering the
high purchase price of the unit...
Recently, I was cooking the evening
meal on my Belling stove which has
an induction cook-top. About halfway
through cooking, the stove went BANG
and the cook-top stopped working. I
rushed around and found a portable
butane cooker to complete the stir-fry.
After dinner I searched out the warranty and purchase documents for
the stove; it had a 2-year warranty
but the purchase was three years ago.
Not good.
Knowing that the induction cooktop was the most expensive part of
the stove, I was thinking this problem
was going to be expensive. With this
in mind I was keen to investigate the
problem and possibly repair it. To this
end I began to dismantle the stove.
It was not too hard to remove the
glass top as a unit, before which I had
pulled the fuse on the stove circuit.
To remove the top required removing
four screws at the back and disconnecting the power supply to the induction top and also unplugging the
signal wire connections to each of the
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control knobs on the front of the stove.
Laying the stove-top upside down, I
was able to remove the screws around
an aluminium tray which held the induction unit under the glass top. Turning the tray over it, was a simple matter to click out the induction coils and
unscrew their cable connections to a
circuit board.
The coils had to be removed to get
to the Torx screws which held a plastic
tray to the aluminium tray. This tray
has three circuit boards clipped into
it. Once the plastic tray was free it was
a simple matter to clip out the circuit
boards after marking and disconnecting the power cables and digital cable
connecting to a small control board.
Looking for the cause of the BANG,
on removing a power filter board I
found that underneath was a large
black soot and vapourised copper
splatter on the board and in the plastic tray.
After scrubbing all of the splatter
off the board it was clear what had
happened. This board had a narrow
track, with slots punched each side,
designed to be the fuse. To support this
analysis, on top of the board paralleling this track is provision to install a
proper 240VAC-rated fuse.
Therefore to make the repair I installed an appropriately-rated glass
mains fuse. There was another similar fuse on the other edge of the board
which I also replaced with a glass fuse
and then cut the copper track. Having
repaired the fuse I had to then determine the reason for the fuse blowing.
On the induction heating coil driver
board, there is a power transistor and
large capacitor for each cook plate.
Checking the large transistors with an
ohmmeter, I found that one transistor
was clearly fused (zero ohms between
all leads).
On looking at the board markings
the three leads on the transistor were
marked C, E and G – odd; I have not
seen a transistor marked this way. Using a solder sucker I unsoldered this
transistor, and to remove its heatsink
I was able to use a long clamp to pull
the clip sideways to cause it to pop
out of the groove; I did not want to
deform the spring in the clip so that
it could be reused.
Once the transistor was out I
could read the markings “TOSHIBA
40RR21”. Finding the datasheet on the
internet, it is an Insulated Gate Bipolar Transistor (IGBT) and “Dedicated
siliconchip.com.au
The underside of the stove-stop which shows the various induction coils and
their cable connections to the circuit board below. These coils were removed so
the aluminium tray could be unseated and the circuit board freed.
to Voltage-Resonant Inverter Switching Applications”. The resonant circuit appears to be formed with a large
capacitor and the induction coil for
each hot plate.
Being a specialised device I was not
so confident I would be able to find
a replacement. However, a Google
search found a replacement at www.
aliexpress.com
My stove cook-top is now working
as before, except next time I should not
have to clean up all the spatter and a
fuse blow-out will be safer.
SC
One of the power transistors on the induction heating coil driver board had
fused and needed to be replaced.
Celebrating 30 Years
December 2017 65
Build your own Super-7
AM RADIO
RECEIVER
Part II – by John Clarke
All on a
single PCB
– and no SMDs!
In this second and final article on the new Super-7 AM Radio, we show you
how to assemble it, then align it for best performance. Then you can put it
into its superb acrylic case . . . and your friends won’t believe you built it!
A
ssembly is not at all difficult –
everything is mounted on one
large PCB and we don’t use
any SMD components – so it’s standard soldering all the way.
And don’t be put off by alignment:
it’s not hard to do and can be done using quite basic equipment, as we will
explain shortly.
Of course, it can also be even better
using specialised equipment, such as
the Dead-Easy DDS Superhet IF Align66
Silicon Chip
ment Unit we published in the September 2017 issue (www.siliconchip.
com.au/Article/10799).
As its name suggests, this makes
alignment, or adjustment of the IF
coils, on the Super-7 AM Radio . . .
dead easy! (see the panel on page 73).
But if you can’t justify building a device such as this, there are other ways
to do it; maybe not quite so simple or
elegant but effective nevertheless. We
will cover other approaches to align
Celebrating 30 Years
the radio set shortly.
There are a number of test points
on the circuit board which can be
used for voltage measurements or to
provide signals to be displayed on an
oscilloscope.
We will show some typical waveforms in this article, so you will know
what to expect.
Fortunately, you don’t need an expensive ’scope for this – indeed, there
are any number of 1MHz bandwidth
siliconchip.com.au
kit models available on ebay and similar (ie, you build them first!) for well
under $100.
And if you’re at all into hobby electronics (or above) you really do need
an oscilloscope on your bench. Spend
a little more and you can get a really
good, higher bandwidth scope which
will suit your needs for many years.
Construction
The Super-7 AM Radio is built on
one double-sided PCB coded 06111171
and measuring 313 x 142.5mm.
It is housed in a multi-piece acrylic case, available from the SILICON
CHIP Online Shop. This also includes
a transparent tuning dial. Station
call signs (eg, RN for Radio National) and frequency markings that are
screen-printed on the PCB can be seen
through it.
The Super-7 AM Radio uses some
special AM radio parts. These include
a coil pack, a mini tuning gang capacitor and ferrite rod with coil. Otherwise,
most of the parts are pretty common –
you may have many of them in your
“junk” box.
Fig.1, the circuit, was published last
month. Fig.2 (overleaf) is the overlay
diagram and this shows where all the
components go on the PCB. Use this
(and the photos) as a reference while
following these instructions to fit the
components to the board.
Begin construction by installing the
resistors. Their colour code table is
shown on page 70.
We suggest that you also check each
resistor value with a digital multimeter before it is inserted – some colour
bands appear close to others (eg, red,
brown and orange) so it is always wise
to double check, especially before you
solder them in!
Resistors are not polarised – they can
be inserted either way into the board
but it is a good idea to install them so
that their colour codes all align in the
same direction. This makes it so much
easier to check their values later on.
Fit the PC stakes for the GND (TP
GND), two near CON2 (for the speaker),
one at TP1 and five for VR1. Three of
the PC stakes for VR1 are to wire it to
the board, while the remaining two are
to solder to the potentiometer body to
hold it more securely. This pot is installed later.
Next, install the capacitors. There
are three types used in the circuit.
One type is MKT polyester (plastic)
and these can be recognised by their
rectangular shape. These are not polarised. The second type is ceramic and
these are also not polarised. Fortunately, they are all the same value too, so
you can’t get them mixed up!
Generally, small capacitors are not
marked with their actual value – instead, they use a code which you need
to decipher. We make that particular
task easy with the small capacitor code
table, also on page 70.
The third type of capacitors used
in this project are electrolytics – they
are polarised and must be inserted the
right way around – follow the markings on the PCB overlay. Electrolytics
are (usually) cylindrical in shape, with
a polarity stripe along one side for the
negative lead. The opposite (positive)
lead is usually the longer of the two.
Almost invariably, electrolytic capacitors will have their actual value
printed on them, along with their voltage rating.
One point which often confuses beginners: it is normally OK to use an
electrolytic capacitor (or indeed any
capacitor) with a voltage rating higher
than that specified, as long as there is
room (capacitor size normally increases with voltage). However, it is not OK
to use capacitors with a lower voltage
rating than that specified.
For example, if a circuit calls for a
10µF, 16V electrolytic capacitor, you
can normally use one of the same value
and type – 10µF electrolytic –with a
25V, 35V or even higher rating, as long
The Super-7 AM Radio Receiver in its
purpose-designed acrylic case. The majority of the case panels
are high-gloss black but the rear panel is crystal clear, (hence the
reflections), just so others can see your handywork in all its glory!
siliconchip.com.au
Celebrating 30 Years
December 2017 67
Fig.2: this PCB overlay diagram shows where to fit the components onto the board before soldering. Ensure polarised
components (diodes, electrolytic capacitors and transistors) are the right way around. Also pay careful attention to ensure
each component installed is of the correct value and type. The four transformers have colour coded slugs, as shown.
as it will fit. However, you generally
cannot use a 10µF electrolytic capacitor with a 6.3V rating – it is liable to
explode! But in this circuit, you could
use capacitors with a 10V rating, since
the battery voltage is only 9V.
OK, back to construction: install diodes D1, D2 and D3. While they may
look identical, each diode is a different type so don’t mix these up. Diodes
are also polarised. The polarity band
or stripe, which indicates the cathode
(k), is oriented toward the bottom of the
PCB as shown on the overlay diagram.
The transistors go in next. Again,
make sure you put the correct transistor
in each position. Transistors Q6 and Q7
are mounted horizontally with leads
bent over at 90° so that their holes line
up with the holes in the PCB.
The Q6 & Q7 transistor bodies are
attached to the PCB with M3 x 10mm
68
Silicon Chip
screws and nuts with the screw placed
from the rear of the PCB and the nut
on the transistor. (The copper of the
PCB acts as a “heat sink” to keep them
from overheating).
The remaining transistors don’t handle as much power so they are smaller
types which are mounted vertically on
their leads. You may need to splay their
leads out to fit the mounting holes on
the board (eg, using small pliers). Make
sure the “D”-shaped packages (looking
down on them) go the same way around
as shown on the overlay diagram.
IF transformers
Now you can install the oscillator
and IF transformers. They will only
go in one way with three pins on one
side and two on the other.
However, these all look the same except for the colour of the slug at the top.
Celebrating 30 Years
The colours are as follows: the oscillator transformer (T2) is red; both the
(identical) IF transformers (T3 & T4)
are white; the third IF transformer (T5)
is black. The mounting positions for
each of these transformers are clearly
indicated on the PCB.
By the way, resist the temptation to
twiddle the slugs of the IF transformers and oscillator coil, especially using
a small screwdriver. There are several
reasons not to use a small screwdriver
to adjust the slugs.
First, it is all too easy to crack the
slug since these are brittle and once
broken will be jammed in the transformer core.
Second, the blades of screwdrivers are often magnetised and this can
affect the magnetic characteristics of
the slugs.
Third, when you are aligning the rasiliconchip.com.au
off with sidecutters.
We want to solder the pot body to the
PC stakes to hold it securely in place
but the body is normally “passivated”
to prevent corrosion. This makes it
almost impossible to solder – so you
will need to scrape the pot sides with
a hobby knife to remove some of the
passivation before soldering.
Pass the potentiometer through the
PCB from the component side and secure it with its washer and nut on the
“top” or label side. Bend the tags so
that they touch the PC stakes on the
board and solder them in place.
Trimpot VR2, for the audio amplifier output biasing, can also be installed
at this stage, followed by the battery
holder, on/off switch and headphone
socket. The battery holder is held in
place with self-tapping screws. The
power switch and headphone socket
are mounted directly on the board.
Speaker mounting
dio, the steel blade of the screwdriver
will affect the resonance of the coil and
you will get misleading results.
You should use a set of plastic alignment tools (they’re quite cheap) and
use one which has a blade that’s a neat
fit in the slot of the slug.
If you can’t purchase a suitable alignment tool, you can make one out of a
piece of scrap plastic shaped at one end
so that it is like a screwdriver blade
and sized to neatly fit the slug slot. You
can easily do this with a sharp utility
knife and needle files. Many a plastic
knitting needle has disappeared from
mum’s sewing basket over the years to
make alignment tools!
When installing the ferrite rod antenna, secure the ferrite rod in place
with cable ties but keep them loose
for the moment, as you will need to
adjust the coil position later during
alignment.
The coil on the ferrite rod has four
very fine cotton-covered coloured
siliconchip.com.au
wires. Keep these the length that they
are, ie, do not cut them short, since
they are already pre-tinned.
The circuit board connections for the
antenna coil connections are labelled
with the colours: clear (CLR), black
(BLK), red (RED) and green (GRN). The
clear wire is the one that is at the far
end of the coil and is separate from the
remaining three wires.
The plastic dielectric tuning capacitor (or tuning “gang”) is normally supplied with two tiny M3 screws which
are used to secure it to the PCB. After
these are inserted and tightened, the
three tags need to be bent at right angles to insert into the holes on the PCB.
They are then soldered in place.
You’ll need a hacksaw to cut the
volume control potentiometer shaft
to 17mm in length (from where the
threaded boss starts). There is a small
location spigot on the side of the pot,
which is not needed, so it can be
snapped off with a pair of pliers or cut
Celebrating 30 Years
The speaker is fastened directly to
the PCB using four M3 screws and nuts,
with short lengths of hookup wire between the loudspeaker and speaker
PC stakes.
Note that there are eight speaker
mounting holes, two sets of four on two
different circumferences. So select the
correct holes for your particular loudspeaker and orient it so the terminals
are nearest to CON2.
Now check all your work very carefully and you will be ready for the next
stage which is alignment.
Aligning your radio
The major difference between this
project and any other that you may
build is the need for alignment. Even if
you have assembled the radio precisely as we have described so far, there is
little chance that it will work satisfactorily when you first turn it on.
This is because even tiny variations in component values and characteristics and even slightly different
PCB track widths and fibreglass thickness can cause frequency shifts which
throw the workings of the radio off.
There are various adjustments to
compensate for this, including the adjustment slugs in the IF transformers,
which need to be “tweaked” to give
the best gain and frequency response.
You will also need to adjust the slug
in the oscillator coil and the trimmer
capacitors associated with the tuning gang to give the best tracking. The
December 2017 69
Fig.3: this shows the
locations of the antenna and oscillator
trimmer adjustments on the tuning
gang.
resonant circuit of the oscillator (T2,
VC3 and VC4) must track with the aerial resonant circuit (T1, VC1 and VC2)
across the whole of the broadcast band.
Otherwise, the set’s sensitivity will
vary quite markedly as you tune it.
This also helps to ensure that stations
appear at their correct locations on the
tuning dial.
Before you start the alignment process, rotate trimpot VR2 fully anticlockwise. This will reduce the quiescent current in the output stage transistors, Q6 and Q7, to zero. Rotate the
volume control pot and the tuning
knob fully anticlockwise too.
This done, connect a 9V battery or
9V DC power source (a 9V DC plugpack or 9V power supply – but make
sure the centre pin is positive) and then
measure voltages around the circuit.
Connect the negative probe of your
multimeter to the GND test point and
then verify that the following voltages
are correct:
TP+ (8.88V), TP1(1.55V), TP2
(8.88V), TP3 (1.1V), TP4 (8.88V), TP5
(1.78V), TP6 (9V), TP7 (4.7V), TP8
(4.3V), TP9 (3.73V), TP10 (4.2V).
In each case, the voltage should be
within about 10% of the value noted
above assuming that the supply is exactly 9V. If the voltages are quite different from the values listed above, then
you should investigate why. For example, if your supply is actually putting
out 9.5V then the readings which are
supposed to be 8.88V could easily be
9.38V instead (and TP6 will be 9.5V).
By the way, these voltages are ‘no
signal’ voltages. That means little or
no signal should be picked up by the
input stage and the volume control is
turned down so that there is no signal
going through the amplifier stages. The
presence of signals will alter these voltages, although not greatly.
You can also measure the current
drain now. This can be done by connecting your multimeter (selected for
measuring a low current range) across
the on/off switch between the centre
and rear terminals at one side of the
switch. Alternatively, connect the multimeter between the anode of diode D3
and the 9V battery positive terminal.
With the switch set switched off,
the current through the meter should
be less than 10mA. We measured 3mA
on our prototype. If you measure a lot
more (more than 10mA) or a lot less
(under 1mA), disconnect the multimeter and check the board carefully
for assembly errors, solder bridges, etc.
Aligning the IF stages involves injecting a 455kHz signal into the front
end of the circuit. As mentioned, earlier, the DDS IF Alignment unit from
September 2017 makes this easy. See
Resistor Colour Codes
Qty Value
4-Band Code (1%)
5-Band Code (1%)
1
1.2MΩ* brown red green brown
brown red black yellow brown
1
1MΩ
brown black green brown
brown black black yellow brown
1
820kΩ grey red yellow brown
grey red black orange brown
1
47kΩ
yellow purple orange brown yellow purple black red brown
1
39kΩ
orange white orange brown orange white black red brown
1
27kΩ
red purple orange brown
red purple black red brown
1
22kΩ
red red orange brown
red red black red brown
1
12kΩ
brown red orange brown
brown red black red brown
1
10kΩ
brown black orange brown
brown black red brown
1
4.7kΩ
yellow purple red brown
yellow purple black brown brown
2
3.3kΩ
orange orange red brown
orange orange black brown brown
1
2.2kΩ
red red red brown
red red black brown brown
2
1kΩ
brown black red brown
brown black black brown brown
1
470Ω
yellow purple brown brown yellow purple black black brown
1
100Ω
brown black brown brown
brown black black black brown
* 1.2MΩ 5% carbon can be used: its colour code will be brown red green gold
70
Silicon Chip
Celebrating 30 Years
Small Capacitor Codes
Qty
3
1
4
1
1
Value/Type
100nF ceramic
47nF polyester
22nF polyester
10nF polyester
4.7nF polyester
EIA
104
473
223
103
472
IEC
100n
47n
22n
10n
4n7
the side panel on how to do this.
The alternative is to connect an RF
oscillator, set to 455kHz, through a
1nF ceramic capacitor to test point
TP1. If you don’t have an RF oscillator, you could use an audio signal generator set to produce a square wave at
152kHz with an 800mV output level.
Since a square wave produces odd order harmonics, it is the third harmonic (3 x 152kHz) from the square wave
at 456kHz that will be your signal for
the IF alignment.
Connect your multimeter (set to read
DC volts) between test point TP3 and
ground. Set the RF generator to give a
signal output of about 1mV RMS or the
audio signal generator square wave to
800mV RMS. The idea is to now adjust
each of the slugs in the IF transformers in turn for a minimum voltage on
test point TP3.
As you adjust the slugs, the gain of
the IF stages improves and the signal
fed to the detector diode (D1) increases. The detector diode rectifies the IF
signal and so, as the signal increases,
the negative voltage produced by the
detector increases. Hence, the voltage
at test point TP3 decreases.
Note that after adjusting all the slugs,
you may wish to go back through them
again and check that they are all set
at their optimum position. It’s sometimes possible to make improvements
the second time around that were hard
to see initially.
Oscilloscope method
If you have access to an oscilloscope,
you can connect it to TP6 and observe
the IF signal directly.
Now, as you adjust the slugs, you
will see the signal increase or decrease.
Adjust the slugs for the best possible
(ie, highest) signal amplitude.
If you notice any clipping of the signal at TP6, just reduce the signal input
from your RF oscillator.
Tracking adjustments
These adjustments ensure that the
RF input circuit and the local oscillasiliconchip.com.au
Scope1: voltage at the collector of Q1 with the set tuned
to around 700kHz 700kHz + 455kHz = 1.155MHz). You
can see that the oscillator waveform is a clean sinewave
with an amplitude of around 350mV RMS.
tor cover the correct range of frequencies so that you can tune over the entire
broadcast band. Ideally, you need an
RF signal generator to do this task. If
you don’t have access to one, you will
have to rely on tuning stations at the
top and bottom of the band.
In Australia, the broadcast band is
specified as 531-1602kHz, so to be
sure you are covering this band, it is
normal to make a radio tune over a
slightly wide range, eg, 525-1620kHz.
If you are in an area where there are
“out of band” AM stations, such as
narrowcasting community stations up
to about 1711kHz, you need to make
the receiver tune slightly higher again.
(See www.acma.gov.au/theACMA/
narrowband-area-service-licensing).
Let’s first proceed on the basis that
you have an RF signal generator. If you
don’t have an RF signal generator, see
the section entitled “Setting the tuning range without an RF generator”.
With signal applied to TP1 via a 1nF
Scope2: now a test signal has been coupled into the
ferrite rod. The test signal was modulated onto a 720kHz
carrier. You can see the effect of signal modulation in the
thickening of the trace away from the centre.
capacitor, set the generator to 525kHz
and rotate the tuning knob fully anticlockwise. This sets the plates of the
tuning gang “in mesh” which is the
maximum capacitance condition, for
the low-frequency end of the band.
Now adjust the slug in the oscillator coil for maximum loudness of the
signal via the speaker, or (if you are
using an oscilloscope) for maximum
signal amplitude at TP6.
Next, rotate the tuning knob so that
it is fully clockwise. Set your RF signal generator to 1620kHz. Tune the
adjustment screw on the back of the
tuning gang labelled “oscillator trimmer” (see Fig.3) for maximum signal
amplitude, as before. Rotate the tuning
knob fully anticlockwise and redo the
oscillator coil slug adjustment again
at 525kHz.
This done, go back to the top of the
band at 1620kHz and adjust the oscillator trimmer again. The adjustments
need to be done a number of times as
the top adjustment affects the bottom
adjustment and vice versa.
You have now adjusted the oscillator range so that the broadcast band
can be tuned in and this also ensures
that the stations are tuned in at the locations indicated on the dial.
As a point of interest, the oscillator
will now be tuned over the range 9802075kHz. That’s 525kHz plus the IF
of 455kHz to 1620kHz plus 455kHz.
Now you need to adjust the ferrite
rod coil and antenna trimmer (on the
back of the tuning gang) to maximise
sensitivity by ensuring the aerial circuit is resonant at the tuned frequency.
Set the tuning knob fully anticlockwise and set the RF signal generator
to 525kHz, then move the coil along
on the ferrite rod until the signal amplitude is at a peak.
You may have to (carefully!) heat up
the coil with a hot air gun to melt the
wax between the coil and ferrite rod,
before the coil can be moved.
Setting the tuning range without an RF generator
In the accompanying procedure for setting oscillator and antenna tracking, we assumed that you had access to an RF signal
generator. For many constructors, this won’t be the case and they
will have to rely on broadcast signals at the top and bottom of the
broadcast band.
However, this poses something of a ‘chicken & egg’ situation.
How do you do the tracking adjustments if you cannot receive the
signals? In most cases, you should be able to receive signals at
or near the bottom of the broadcast band especially at night (typically high power ABC radio stations). For example, in Sydney, you
can tune in to ABC Radio National at 576kHz.
However, picking up a signal at the top end of the band might
not be anywhere as easy. The highest frequency nationwide AM
radio station is In Sydney, the highest commercial AM station is
at 1269kHz (2SM). Above that, there are only community and narrowcast radio stations which may not be strong enough to use for
siliconchip.com.au
this purpose in all areas of the city.
But there is a solution if you have another AM Radio since every
superhet has a local oscillator and for an AM broadcast receiver,
this oscillator will usually be 455kHz above the tuned frequency.
Therefore, you can use the local oscillator in your other AM radio
to set the tracking adjustments at the top of the band.
The method to follow is this: place the ferrite rod of the Super-7 AM Radio near the antenna rod other AM radio. This rod
will usually be at the top of the case. Rotate the tuning dial of the
Super-7 AM Radio fully clockwise to tune to the top of the band.
Tune your other AM radio to 1165kHz or as close to this as you
can. This will set its local oscillator to 1620kHz. That’s the top of
the band on the Super-7 AM Radio’s dial.
As you do so, you should be able to hear faint heterodyne whistles from the speaker of the AM radio. Now proceed to peak the
antenna and oscillator circuits as described in the article.
Celebrating 30 Years
December 2017 71
Scope3: waveform across the speaker with VR1 at its
minimum setting and a ~1kHz modulated RF test signal
inductively coupled into the antenna. The zero crossing
artefacts are quite severe with no quiescent current.
Now set the RF generator to 1620kHz
and turn the adjustment screw on the
back of the tuning gang labelled “antenna trimmer” (see Fig.3) until you
peak the incoming signal again.
You should now repeat these adjustments for the optimum response.
When this is done, the ferrite rod coil
should be fixed in place by re-melting
the wax and allowing it to set. That
completes the alignment of the radio.
Quiescent current
All that remains to be done is to set
the quiescent current in the audio power amplifier by means of trimpot VR2.
The best way to adjust the quiescent
current is to feed a sinewave modulated signal into the front end of the radio
from an RF signal generator.
Connect an oscilloscope to the output at test point TP10 and adjust the
volume control for a signal amplitude
across the speaker of about 2-3V peakto-peak. At this stage, VR2 should still
Scope4: the audio output sounded very raspy when
capturing Scope3. We then rotated VR1 clockwise until
the sound became much cleaner and took the screen grab
shown here. The signal looks much more like a sinewave.
be fully anticlockwise. If you now have
a look at the signal on the scope screen,
you will see the classic sinewave with
crossover distortion with notches in
the waveform at the crossover point
(see Scope3).
Now rotate VR2 slowly clockwise
and you should see the crossover nicks
disappear from the waveform and, at
the same time, the sound should become cleaner.
Rotating VR2 to reduce the crossover
distortion will not increase the current
drain by much (typically no more than
a milliamp) but it will make a big difference to the sound quality.
No ’scope?
If you don’t have an oscilloscope,
you can apply a signal at 1kHz from an
audio generator (100mV is suitable) to
the centre of VR1, with VR1 set to mid
position. This will apply audio directly
to the amplifier.
Adjust VR2 for minimum distortion either by listening to the sound
(it should become “pure” with adjustment) or by monitoring on an oscilloscope.
By the way, you should measure the
current drain of the radio while you are
adjusting the quiescent current with
trimpot VR2.
Typically, the current drain of the
radio at 9V should be less than 10mA
when the volume control is at minimum setting (ie, no signal through the
audio amplifier stages).
With the volume control well advanced, to make the radio quite loud,
the current drain may be 40mA or
more.
Don’t rotate VR2 any more than necessary as this will increase dissipation
in the output transistors and will flatten the battery faster when listening.
If in doubt, back it off a bit (rotate
it anti-clockwise) until you hear an
increase in distortion, then rotate it
a tiny bit clockwise until that distortion is gone and you are near the ideal setting.
Note that using the radio with high
Here’s the completed
Super-7 AM Receiver sitting on the
four screws which secure it to the front panel.
Don’t fit nuts over the PCB yet: it needs to be free to move as you slot in
the right-hand end panel, which itself slips over the power switch and headphone socket.
72
Silicon Chip
Celebrating 30 Years
siliconchip.com.au
volume will flatten the battery much
more quickly than at low volume . . .
The acrylic case
Because it is self-contained (ie, fully on one PCB) the Super-7 AM radio
would be quite happy working without a case. But if you want a really
professional finish, you’ll want to put
it into the purpose-designed acrylic
case. Its appearance is not unlike the
mantel radios of yesterday . . .only it
is shiny black!
The case measures 327 x 155 x
58mm (w x h x d) and the front,
sides, top and bottom are made
from a very smart high-gloss black.
The back panel is transparent so
everyone can admire your handywork!
Provision is made in the left end
panel for the on-off switch, a DC power plug and the 6.5mm headphone
socket.
On the front panel, attractive slots
are milled for sound output immediately in front of the speaker and at the
right end there’s a matching 105mm
hole for the clear acrylic tuning “dial”
which reveals the screen-printed PCB
underneath with its major radio stations.
While you can easily move the tuning dial with your fingers, we gilded
the lily somewhat by gluing a large
knob to the centre of the dial (a knob
makes it easier to find elusive stations!)
– whether you add a knob is entirely
up to you. Immediately underneath
and to the left of the tuning dial is the
single “volume” control
The case simply slots together and
everything is held in place by four
50mm long pillars which go from front
to back – more on these shortly.
We’ve also made provision on the
bottom front of the case for a pair of
rubber feet which can angle the whole
receiver back slightly. Again, this is
entirely optional.
Putting the case together
Remove the nuts from the volume
control pot and headphone socket,
if fitted. It doesn’t matter if the clear
acrylic “dial” is fitted to the tuning
capacitor; it can be done now or later.
Start with the front panel. Insert four
M3 x 15mm screws through the four
holes near the edges and put a washer
and nut on each to hold them in place.
Now slide the receiver PCB down over
these screws, obviously oriented so the
siliconchip.com.au
speaker sits behind the slots and the
dial markings behind the 105mm hole.
Slide the left end panel into its slots
on the front panel, at the same time
engaging the on/off switch shaft and
the 6.5mm headphone socket. You will
probably have to lift the PCB on this
end to allow this.
When in position, refit the nut onto
the headphone socket – this will hold
the end panel in place.
Now you can slide the bottom, top
and right end panels into place, with
their tabs fitted into the slots on the
front panel and each other.
Threaded standoffs
It’s not easy (impossible?) to buy
a threaded standoff long enough
(45mm+) to hold the rear panel onto
the front panel. If you can find (or
make!) a 45mm M3 threaded standoff,
more power to you!
We made ours with a combination
of 15mm and a 25mm M3 threaded
standoffs, M3 studs to join them into
single 40mm lengths, plus a few M3
nuts and washers to end up with the
50mm length required.
The “stud” which joins the 15 and
25mm lengths was simply a short
(15mm) M3 screw with its head cut
off with a hacksaw. (You will probably need to run a nut over the cut-off
section to reform the thread).
Two M3 nuts were used between the
two standoffs as spacers. Fig.4 shows
this a little more clearly. The overall
length of the standoff, top of PCB to
bottom of rear panel, is 50mm. Given that nuts vary all over the place
in height, simply choose the number
of nuts and/or washers to make your
standoffs 50mm long.
We made four of these. The bottom
BACK PANEL
Fig.4: you
need four 50mm
M3 threaded
~10mm
standoffs – but
M3 SCREW
just try to buy
them! We made ours
from 15mm and 25mm
standoffs, joined with
an M3 “stud”
M3 NUTS
made from
+ WASHERS
(SPACE AS
REQUIRED TO
a headless
ADJUST LENGTH)
15mm M3
screw. Nuts
and washers
~15mm
M3 SCREW
were used
to pack it
PCB
out to 50mm
long.
FRONT PANEL
25mm M3
TAPPED
STANDOFF
ends screw onto the M3 screws which
pass through the case front panel (with
a nut) and then the PCB. The top ends
fasten to the four M3 screws which hold
the rear panel in place.
SC
Using the DDS Superhet
Alignment Unit ( Sept 17 )
The DDS IF Alignment unit makes aligning the Super-7 quite straightforward.
While its IF alignment mode is handy for
verifying the alignment is correct, the AM
modulated signal generator is actually the
mode we used the most during alignment.
The DDS module allows you to generate the 455kHz, 525kHz and 1620kHz
test signals with or without modulation.
Simply enter the required frequency and
select sinewave mode.
We simply produced a maximum (or
near maximum) amplitude signal and fed
it to a small wire loop which we placed
near the ferrite rod. However, you could
also use the onboard attenuator to produce a lower level signal suitable for direct injection via a 1nF capacitor, as per
the main text.
Note that we found proper alignment
much easier with the aid of a scope since
this allows you to see how cleanly the
modulated test signal is being demodulated and you can tweak the alignment to
give not only the strongest but also least
distorted signal output.
Once you’ve completed the alignment
procedure as stated in the main text, you
can then set the generator frequency and
switch to IF alignment mode to verify that
the IF bandwidth peaks around 455kHz
and has the correct ~10kHz bandwidth to
the -3dB points, as shown in the screen
photo below.
~15mm M3
STUD
(15mm M3
SCREW WITH
HEAD
REMOVED)
50mm
15mm M3
TAPPED
STANDOFF
Celebrating 30 Years
M3 NUTS
+ WASHERS
AS REQUIRED
December 2017 73
Sale ends December 31st 2017.
www.altronics.com.au
1300 797 007
Build It Yourself Electronics Centre®
Gifts ‘n’ Gadgets
Get an ultra-close
up view!
115
$
M 8194
NEW!
49.95
$
X 3070
Acrobatic Mini Drone
SAVE 10%
Must have
for summer
road trips!
USB Car Jumpstarter
& 2-in-1 Floodlight
Includes jumper
leads, charger & case!
This high resolution 12
megapixel USB micrsocope
allows close up inspection of
just about anything! USB PC
interface, plus HDMI output
for monitor connection. 220x
magnification with 10-50mm
focal length. 2.4” LCD
289
Nifty little copter for flying up
to 30m - it even does acrobatic
flips. Easy to charge at home
or in the car with USB. ≈5 mins
flying per charge. Requires 4xAAA
batteries (S 4949B $3.95). Drone
size: 75 x65 x 25mm.
$
Records
1080p
video!
X 4306
Controller doubles
as a storage case.
NEW!
A must have for winter driving! Starts cars from
dead flat. • 300 cranking amps • Fits in your glovebox
• High power LED flood light • Narrow beam torch
• USB phone charging • Suits 12V vehicles only.
NEW!
A 2795
NEW!
Upgrade your alarm clock to digital radio!
X 3090
17
.95
$
129
$
The Amazing HoverBall!
Awesome stocking stuffer to keep you busy on Xmas
morning! Burn off a few fruit mince pies and play indoor
hover soccer with the kids. Requires 4xAA batteries
(S 4955B $3.95).
120
$
C 5062
Edifier® Active Bookshelf Speakers
Amazing value for well under $150. They are perfect for
pairing with your TV or in the study for music and gaming.
Powered design requires no amp! Sleek black wood grain
finish. Dual analog RCA inputs. Model: R1010BT. Size: 151 x
173 x 233mm
SAVE 40%
NEW!
K 2546
20
$
‘Learn To Solder’ Zoo Animals Kit
Play with LEDs, battery & bring each of the six
animals to life! Contains everything you need to
create simple circuits & learn to solder. Age 6+
D 2039
89.95
$
Take your tunes with you!
Waterproof Bluetooth Hi-Fi System & Battery Bank. Great
for the outdoors, fits into your backpack with ease. 5 hour
playback time with 4000mAH internal battery bank (also
charges your devices!). 268x70x100mm, 840g.
Build It Yourself Electronics Centres
» Virginia QLD: 1870 Sandgate Rd » Springvale VIC: 891 Princes Hwy » Auburn NSW: 15 Short St
» Perth WA: 174 Roe St » Balcatta WA: 7/58 Erindale Rd » Cannington WA: 5/1326 Albany Hwy
More channels, more choice. The ideal bedside companion to wake up to
your favourite digital or FM station. Large colur TFT display shows time and
scrolling digital radio info. (displays analog clock and date when radio is off).
20 channel presets. Two alarm times. Size: 135L x 110W x 90Hmm
Two Way Bluetooth
Wireless Audio
Transmit audio from your TV to
your headphones. Or use it the
other way and send music from
your phone to your amp. Uses
low latency technology so theres
no lip sync issues!
A 1103
79.95
$
Weatherproof Solar
PIR LED Floodlight
A compact weatherproof motion
activated light with two activation
modes. Rear facing dim light with
front motion activated bright light.
Solar powered. 145W x 96L x
75Dmm. 220 lumens.
29.95
$
NEW!
X 2375
Follow <at>AltronicsAU
www.facebook.com/Altronics
NEW!
True RMS
Autoranging
Meter
NEW!
A price breakthrough for
accurate True RMS AC
measurement! Packed
with features for under
$40. Includes carry bag
and test leads.
39.95
$
SAVE
$90
Q 1130B
SAVE $60
199
$
Q 1069
139
It’s waterproof! It’s rugged!
It’s built like a tank.
This new meter is built tough with water
and dust resistance, plus a impact resistant
case for the rough and tumble of every day
use in the field. Auto ranging design offers
a feature list as long as your arm with a
clear large digit backlit display. Includes
carry case and test leads. See web for full
spec list.
29.95
$
Ideal for service departments & circuit development.
Provides true RMS measurement & datalogging. 240V
powered. 10A AC/DC. Frequency to 50MHz. Software,
temperature probe, PC leads included. 2 year warranty.
Q 1289
The perfect beginner,
student or enthusiast
multimeter. 12 auto
ranging test modes with
good accuracy and an
easy to read jumbo digit
4000 count screen.
Includes carry bag and
test leads.
Measure
temperature
without touching.
Sound Level Meter
A useful tool for tuning high end
home theatre & car audio systems.
Measures sound up to 130dB.
Great for live venues,
installers, pubs etc.
Includes battery.
Twin laser beams for precise
measurement between
-50°C and 1050°C with
30:1 optical resolution.
Adjustable emmisivity to
cater for different surfaces. It
even connects to an external
probe. 2% accuracy.
Q 1129
$
True RMS Benchtop DMM
$
The All-Rounder
Student DMM
299
Q 1520
Q 1266
SAVE 25%
33
$
TEST , MEASURE, INSPECT & REPAIR...
NEW!
NEW!
NEW!
T 2699A
Handy USB Soldering Iron
16.95
$
59.95
$
Powered by a USB port! Great for occasional jobs like fixing a dry joint
in an audio cable. Built in switch in the handle and auto sleep mode
ensures safe operation at all times. Includes stand & USB lead.
39.95
$39.95
$
74.95
$
T 2090
22
$
Price Breakthrough
40W Soldering Station!
The pefect balance of value for money and features for
beginners or cash strapped students and enthusiasts.
Slim, lightweight non-slip handle with tip cleaning
sponge and iron safety holder. Full range of
spare tips also available.
T 2120
T 5036
Cut, Polish, Grind, Sand & Carve!
Micron® 172pc Rotary Tool Kit
This workbench essential is just the shot for electronics projects,
crafts, hobbies and odd jobs around the house! Powerful 130W
motor (this is a real power tool!) with variable speed between
8000 and 33000 RPM. Included is a massive accessory kit of
grinding wheels, drills, cutters, sanding discs, polishing pads and
more! And it all stows safely away in a hard plastic carry case.
X 0432
No More Eye Strain!
Grerat gift idea!
This jumbo 5x loupe with LED
lighting provides a crisp clear
view of fine print, circuit boards,
small parts etc. USB rechargeable.
Includes carry case.
15% OFF
Double Sided
Parts Case
Perfect for working in the field!
15 compartments on one side,
plus 10 removable containers on
the other side.
HALF
PRICE!
T 2167
$49
24.50
$
Ultimate 6 In 1 Maker Pens
Show the world you’re serious about building! Features a pen, scale
rulers, tablet stylus, blade screwdriver, philips screwdriver. T 1924
(yellow) also features a spirit level. T 1925 (black) includes bottle
opener. All housed in a tough metal casing.
T 1924
Spirit Level
15
$
T 1925
Bottle Opener
16 In 1 Heavy Duty Ratchet Set
12
3 way high torque ratchet handle with 8 double
ended tips with philips, hex drive, flat blade and
torx. 33-136mm shaft length.
$
.50
Shop online 24/7 <at> www.altronics.com.au
USB Clip On 5x
Magnifier Lamp
NEW
MODEL!
The latest Inspect-A-Gadget
magnifier is powered by a USB port
and provides a crisp, clear view
of your workbench. 430mm long.
1.5m USB lead.
39
$
.95
X 0435
1300 797 007
POWER UP THE HOLIDAYS WITH THESE DEALS.
469
$
NEW!
N 1114 100W
$57.95
45
$
M 8195A
M 8070A
240V mains in a cup holder!
Provides 240V power for charging laptops, small
tools, lamps, chargers and more! 150W rated
(450W surge). Ideal for camping. 12V input.
60mmØ. Modified sine wave.
279
$
Lithium-Ion
Car Jump Starter
Suits 12V battery vehicles. 20000mAh rated
battery provides up to 1000A peak output
when cranking. Two USB ports are provided for
charging devices (like a giant battery bank!). It
also has a super bright 1W LED torch in built.
Dimensions: 178L x 84W x 45Dmm.
SAVE $40
159
$
299
$
NEW!
N 0700
$29.95
20
$
Battery Maintainer
120W Portable Folding Solar Power Kit
Going bush? Have power wherever you go on your next 4WD adventure.
This complete power kit includes 120W panel, solar regulator, battery connection
cables and canvas carry case. 3 stage solar charger ensures your batteries are
alway performing at their peak! Adjustable stand for finding best sun placement.
720x520x70mm (folded).
The perfect go-anywhere power accessory - use it to charge batteries
when you go bush! If you don’t want a permanent solar panel on your
4WD, car or caravan, this fold up solar blanket is a great option. It includes
a regulator and croc clips for direct hookup to your battery.
A complete auto
rescue kit for
the car boot!
N 1120
Provides a trickle of power
to your car, caravan or boat
battery to keep it topped up
when parked for long periods.
355x125mm panel size. Suits
M 8534
7 Stage Battery Charger
99
$
Utilises a microprocessor to ensure your battery is maintained in tip-top condition
whenever you need it. Suitable for permanent connection. Great for boats, caravans
& seldom used vehicles. 4.5A output, 6 or 12V batteries.
NEW!
169
$
Battery Jumpstarter & Air
Compresor Kit.
Features a 16800mAh
battery bank plus
emergency compressor to
top up tyres (max 8 mins
run time). Provides 600A
peak cranking output for
starting 4, 6 and 8 cylinder
cars with flat batteries.
12/16/19V output
provided for powering
devices such as laptops.
May also be used as a USB
battery bank.
M 8198
12V batteries only.
Control Appliances
Remotely
SAVE 22%
N 1112 50W
Portable Solar Blankets
SAVE 30%
54
$
Switch any connected
appliance on or off remotely
from anywhere in the world!
Set schedules, monitor and
control your appliances using
the TP-link Kasa mobile iOS/
Android app. “Away” mode
can give the appearance of
someone being at home when
you are on holiday.
35
$
M 8880
5 Way Intelligent USB Charger
‘Charge IQ’ feature charges a connected device at the
fastest speed. 7.8A max current. 110-240V - great for
travel. Includes mains lead. 73x73x34mm.
P 8148
NEW!
REDUCED!
USB Mains Chargers
1A for phones or 2.1A for
tablets. Fully approved!
16.95 $9.95
$
M 8862 2.1A
M 8861 1.0A
39.95
$
Remote Control Power Saver Kit
A 0345
Cut standby power usage around the home/office by switching
appliances off at the wall. Easy inline connection. RF signal
means it even works behind cabinets. 30m range. Requires
2xAAA batteries (S 4955B $3.95). 10A (2400W) per outlet
D 0509
69.95
$
D 0508
55
$
Big ‘n Beefy Battery Bank
Rugged Waterproof Battery Bank
12000mAH capacity - great for recharging your
drone in your backpack. Keeps devices powered
up whilst out and about. Dual outputs 1A/2.1A.
177x72x24mm.
Must have for tradies, travellers and hikers.
Water and dust proof battery bank to recharge
your phone on the go! 5V 1A output, 5600mAH.
DON’T FORGET THE BATTERIES
THIS XMAS! Quality 40 pc
alkaline bulk packs from $17.95.
Shop online 24/7 <at> www.altronics.com.au
USB Car Charger
With Readout
Allows you to power up
two USB devices in your
car. Max 3.1A. Readout
displays battery voltage
& output current.
M 8623B
17.95
$
1300 797 007
PICK UP A SUMMER PROJECT TO BUILD...
Bluetooth® Arduino
Smart Tank Kit
14.95
Includes
16x2 line
screen
$
Construct - Code - Program
An obstacle avoidance tank robot
which can be modified, tweaked and
upgraded as you level up your skills
with Arduino. Features a solid pair of
tracks with aluminium & acrylic base.
Bluetooth smartphone control.
Great for young
builders looking for a
challenge! 12+
K 9800
Simple Logic Probe Kit
(DIYODE Oct ‘17) A simple 3 state logic probe for
diagnosing circuits, checking output pins etc. Includes
test clip connection lead.
27.95
$
K 9675
MegaStand Acrylic
16x2 LCD UNO Kit
24.95
$
A cut down MegaBox which provides a backlit 16x2 LCD for simple readouts,
plus room to customise the front panel with buttons or IR sensor. UNO
(sold separately) fits neatly behind the screen and provides room for add-on
shields as required.
K 9680
NEW!
189
$
NEW!
Z 6450
NEW!
Build your own jumbo
clock or counter
This handy kit makes one
210x110mm digit and can be
paired with additional digits to
create a clock, number counter etc.
Red high brightness LEDs. Driven
by Arduino ShiftOut.
$92
75
$
19.95
K 2545
$
MintySynth® 2.0 Synth
& Sequencer Kit
27.95
$
K 1138
Solar Wild Boar Kit
Ideal for a DIY science fair, afterschool, or workshop project. Learn
about transmission & motors. 6+
A great intro to electronic music! Plus
learn about electronics and programming
along the way. Requires 2xAAA batteries.
130 in 1
Electronics
Learning Lab
A comprehensive
learning lab with
many hours of
SAVE $40
building. Build a
radio, broadcast
station, organ, kitchen
timer, logic circuits
& more. Requires
K 2208
6xAA batteries (S
4906 lithium 2pk
$4.95ea). 10+
K 9680
7 Segment Driver
Shield Kit
Ideal for Arduino clock/counter
control. Features two on board
74HC595 chips which can be easily
driven using Arduino ShiftOut.
19
$
$16.95
K 8135
Super Stereo Ear Kit
B 0091
This stereo amplifier kit boosts
ambient sound in the surround
area by 50x! Headphone jack
fitted. Requires 3 x AA batteries.
13
$
K 8126
Robo-Voice Changer Kit
Make your voice sound like a robot.
Adjustable pitch and vibrato effect.
Requires 9V battery (S 4970B $3.95).
Sale Ends December 31st 2017
Phone: 1300 797 007 Fax: 1300 789 777
Mail Orders: mailorder<at>altronics.com.au
Vehicle Base
Builder Kits
With individual
motors for each
wheel with acrylic
base for mounting
control and sensor
boards. Ideal
base for your own
Arduino robo-car
design. Includes
battery holder.
SAVE
30%
The BBC micro:bit is a
pocket sized codeable
computer with motion detection,
compass, LED display and
Bluetooth on board. Designed
to be fun and easy to use for
students in coding class rooms.
It even connects to Arduino and
Raspberry Pi! Includes USB lead
and battery pack.
Z 6440
NEW!
Pi sold separately.
Z 6307
Raspberry Pi®
VESA Mount
24
K 1090 2WD
$44.50
30
32.95
$
12
$
K 1092 4WD
K 9670
$
$34.50
$
80
$
BBC micro:bit
GO Kit
A HAT board with soldermasked 0.1” holes and
stackable header so you dont
lose access to the GPIO pins.
Slots included for display &
camera cables.
99
.95
The MegaBox allows an Arduino UNO or Mega to be plugged
into it, along with a shield allowing you to build a design into a
finished case. Plus it also features a 16x2 LCD, four buttons,
rotary encoder, dual 2A 5V relay outs. All pins broken out to
headers for connection to breakouts.
ProtoHAT for
Raspberry Pi®
$
NEW!
MegaBox Kit For Arduino
H 8190
NEW!
15.95
$
Find your nearest reseller at:
www.altronics.com.au/resellers
A versatile acrylic bracket
for mounting the R-Pi behind
monitors - with or without a
bracket! VESA 75 & 100mm
compatible. Includes cable
ties & holes to secure leads.
Case sold separately, H 8957
$11.75.
Please Note: Resellers have to pay the cost
of freight and insurance and therefore the
range of stocked products & prices charged
by individual resellers may vary from our
catalogue.
© Altronics 2017. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude
freight and insurance. See latest catalogue for freight rates.
Using Cheap Asian Electronic Modules Part 11: by Jim Rowe
Elecrow GY-68 & GY-BM
Barometer/Temperature
Sensor Modules
This month, we’re looking at two very tiny modules
which sense barometric pressure and air temperature.
One uses the Bosch BMP180 digital pressure sensor,
while the other uses the newer BMP280 sensor. Both
can send their readings to virtually any micro via a
standard I2C serial interface, while the BMP280-based
module also offers an SPI interface.
T
he first thing you notice about
the Elecrow GY-68 digital barometer module is its tiny physical size.
It measures only 13 x 10 x 2.5mm,
making it by far the smallest module
we’ve looked at so far in these articles.
The BMP180 sensor IC which forms
the functional heart of the module is
much smaller again, measuring only
3.6 x 3.8 x 0.93mm.
The BMP180 has what is described
as ultra-low power consumption,
drawing less than 10µA when taking
readings once per second and less than
1µA in standby mode. Clearly, it’s very
suitable for use in compact portable
devices like smartphones.
It’s also a low-cost device. The
Elecrow GY-68 module we’re looking
at here is available from the Silicon
Chip online shop for just $5 plus postage (catalog code SC4343).
The BMP180 sensor
This is made by Bosch Sensortec,
a division of the large German firm
Robert Bosch GmbH (www.boschsensortec.com). The BMP180 is based
on piezo-resistive MEMS technology,
where MEMS stands for “MicroElectroMechanical Systems”.
In other words, it uses a tiny sensor
element which flexes mechanically in
response to changes in atmospheric
78
Silicon Chip
pressure and the flexing is sensed by
measuring changes in the element’s
resistance.
The BMP180’s 3.6 x 3.8 x 0.93mm
metal package has a tiny vent hole
(about 0.5mm diameter) in the top to
allow the sensor element access to the
outside air. And apart from the sensor
element, there are three other functional blocks inside the device.
As shown in Fig.1, the three blocks
comprise an ADC (analog to digital
converter) to make the measurements,
a control unit which also provides
the I2C serial interface for communicating with an external micro and an
EEPROM which has 22 bytes of storage for the device’s 11 x 16-bit calibration parameters.
Every individual BMP180 device
is calibrated during manufacture,
after which the calibration parameters
are saved in its EEPROM. An external
micro can read these parameters and
use them to correct that sensor’s readings for offset, temperature dependence and other factors.
So with suitable software, the
BMP180 can provide very high accuracy measurements of both barometric
pressure and temperature. The relative accuracy for pressure is quoted as
±0.12hPa from 950-1050hPa at 25°C,
while the absolute accuracy is quotCelebrating 30 Years
ed as -4 to +2hPa over the range from
300-1100hPa and for temperatures of
0-65°C. Impressive!
With the right software, it’s also
fairly easy to use the BMP180 as an
altimeter, capable of indicating your
current altitude above mean sea level
(MSL). So its applications are not limited to being used as a barometer and
thermometer.
By the way, although the BMP180
normally comes with the I2C serial
interface, a variant is also available
with an SPI interface. Presumably, this
would be for large orders from equipment manufacturers.
By the way, if you’re unfamiliar with
barometers and the various units used
for atmospheric or barometric pressure, you might like to refer to the
panel headed “Barometric Pressure
and Units”.
Elecrow’s GY-68 module
As you can see from the photo of the
Elecrow module, there are few components apart from the BMP180 sensor itself: just an SOT-23 low-dropout
(LDO) voltage regulator, three surfacemount capacitors and two resistors.
Fig.2 shows its complete circuit.
REG1 is the MCP1700 3.3V LDO regulator, used to ensure that the supply
voltage for the BMP180 is kept within
siliconchip.com.au
Fig.1: block diagram of the BMP180 (the small metal
package located on the module). It contains 22 bytes
of EEPROM for storing calibration values.
its ratings (3.6V max). It also ensures
that the two pull-up resistors on the
I2C interface’s SDA and SCL are returned to the same safe voltage level.
The three capacitors are for supply
rail bypassing.
CON1 is the 4-pin connector used
both to supply the module with its
power and also to connect to an external micro via the I2C interface. Since
the module draws less than 10µA from
the supply when it’s taking one measurement per second, there’s no problem in powering it from an Arduino or
a Micromite module or from a power
bank using a 3.7V Li-ion cell.
Fig.2: complete circuit for the GY-68 module. CON1 provides
power and I2C interfacing for the module, which draws less than
10µA when taking readings, and 1µA in standby mode.
to the libraries in your Arduino IDE by
clicking on Sketch → Include Library
→ Add .ZIP Library and then directing it to the folder into which the zip
file was downloaded.
On the Silicon Chip website, you
can find a small sketch for running
the GY-68/BMP180 with an Arduino,
called “SFE_BMP180_barometer_
sketch.ino”. I have adapted it from a
sample sketch provided by Elecrow.
It’s pretty straightforward, first initialising the BMP180 (ie, extracting
the calibration parameters from its
EEPROM) and then taking a measurement of temperature and barometric
pressure every five seconds.
Each time it takes a measurement,
it crunches the data and displays the
results on the Arduino IDE’s Serial
Monitor. A sample of this is shown in
the screen grab of Fig.5.
Since the BMP180 only measures
the temperature and absolute air pressure, the sketch needs to know your
current altitude above sea level in
order to calculate the corresponding
MSL pressure.
Connecting it to a micro
Fig.3 shows a simple way of connecting the GY-68 barometer module to an Arduino. The SCL and SDA
lines of the GY-68 connect to the SCL/
A5 and SDA/A4 pins of the Arduino,
while the VIN and GND lines connect
to the +5V and GND pins respectively.
That’s all there is to it.
It’s equally simple to connect the
module to a Micromite, as you can
see from Fig.4. Here the SCL and SDA
lines connect to pins 17 and 18 of the
Micromite respectively, while as before, the VIN and GND lines go to +5V
and GND.
Programming it
It’s relatively easy to get the GY68 module working happily with an
Arduino, although this does involve
the use of a matching software library
called SFE_BMP180.zip. This can be
downloaded from the Elecrow website at https://github.com/sparkfun/
BMP180_Breakout
After downloading, it can be added
siliconchip.com.au
The Elecrow GY-68 module is shown here at three times actual size, as it is only
13 x 10mm. The metal package BMP180 sensor (3.6 x 3.8mm) is based on piezoresistive MEMS technology.
Celebrating 30 Years
December 2017 79
Fig.3 (top): the pin connections for the GY-68 to an Arduino are fairly
straightforward.
Fig.4 (upper right): pin connections for the GY-68 to a Micromite module.
Fig.5 (bottom left): example data from the GY-68 sensor module when connected to an Arduino.
Fig.6 (right): example data from the module when
connected to a Micromite.
Fig.7 (bottom right): when running the Micromite
sample software, if there is a screen attached, it will
also show the readings on the display.
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This information is fed to it in this
line, located very close to the start of
the sketch:
#define ALTITUDE 55.0
This sets the altitude to 55 metres,
which is a rough estimate of my workbench’s altitude above MSL. However, as the comment on the right of this
line explains, you can easily substitute
your own altitude if you want maximum accuracy.
You’ll note from Fig.5 that the sketch
repeats this altitude figure in the first
line of each set of measurements, giving it in both metres and feet. It also
shows the temperature reading in both
degrees Celsius and degrees Fahrenheit as well as the absolute and MSLrelative pressures in both millibars
and inHg (inch of mercury; reflecting
its origin in the USA).
Finally, it repeats the altitude figures
again, but this time describes them as
“computed altitude”. This sketch is a
good way to see what the GY-68 module can do.
It’s not quite so easy to get the GY68 module working with a Micromite
because there is no pre-existing or
built-in library designed to communicate with it and do the calculations
to provide the corrected temperature
and pressures.
However, I have written an MMBasic
program to do the job and you can download it (“BMP180 barometer check prog.
bas”) from the Silicon Chip website.
This program expects a GY-68/
BMP180 to be connected to the Micromite as shown in Fig.4 so once you do
this and upload the program, it should
spring into life.
If you have the Micromite still connected to your PC and have Micromite
Chat open, you’ll see that it produces
temperature and pressure measurements every second, as shown in the
screen grab of Fig.6.
Just as with the Arduino sketch,
this program also needs to know your
current altitude/elevation in order to
work out the equivalent barometric
pressure at MSL.
As before, you need to substitute
your elevation in this line, which
you’ll find near the start of the program and in about the middle of the
declaration of the program’s variables:
DIM AS INTEGER Alt = 50
Simply substitute your own altitude/elevation above MSL (in metres)
instead of the “50” in this line, then
upload the program to the Micromite
and get it going (by clicking on the little “gearwheel” button in the Micromite Chat toolbar). It will then show
the current mean-sea-level pressure
(MSLP) as the last item in each line.
If your Micromite is hooked up
to an LCD touchscreen, it will also
give you an on-screen display of the
temperature and pressure readings
as shown in the screen shot of Fig.7.
Like the measurements sent back to
your PC, the display is updated every second.
Incidentally, I compared the temperature and pressure readings achieved
using this program with the figures
shown on the Australian Government
Bureau of Meteorology website (which
updates every 10 minutes in the Sydney area), and they compared surprisingly well. The temperature was
within 0.2°C and the MSL pressure
within 0.5hPa; not bad at all for such
a small device!
If you want to make your own comparisons, you’ll find the Bureau of
Meteorology website at www.bom.
gov.au
You just have to select your state,
then Observations, then select your
area in the state.
Barometric Pressure and Units
You’ll find quite a few units in use for measuring atmospheric or barometric pressure: Pascals (Pa) and hectoPascals
(hPa), bars (B) and millibars (mB), millimetres of Mercury (mmHg) and inches of Mercury (inHg).
Basically, atmospheric pressure is due to the weight of air immediately above you and it corresponds to a force per
unit area. The primary SI unit for pressure is the Pascal (Pa), which is equivalent to a force of 1 Newton per square metre. That is, 1Pa = 1N/m2.
It turns out that a column of air one square centimetre in cross section, measured from sea level to the top of the Earth’s
atmosphere, has a mass of about 1.03kg and a weight of 10.1325N. This corresponds to a pressure of 101,132N/m2, or
101,325Pa (= 101.325kPa = 1013.25hPa, since 1hPa = 100Pa). So the standard atmosphere is defined as 101,325Pa
or 1013.25hPa.
The actual barometric pressure at any particular location depends upon its elevation or altitude with respect to mean sea
level (MSL), because the higher the elevation, the lower the weight of air directly above you and the lower the pressure.
For low altitudes, it can be estimated as falling by about 10hPa for every 100m rise above MSL. For higher altitudes,
the pressure at any elevation/altitude can be found by a standard expression known as the Barometric Formula.
The first barometers (invented in 1643 by Italian physicist Evangelista Torricelli) used to measure atmospheric pressure used a column of mercury in a vertical glass tube and as a result, they were calibrated in terms of the height of
the mercury column, measured in either millimetres or inches. So that’s where the “mmHg” and “inHg” units of pressure came from.
In fact, “inHg” is still used in the United States, Canada and Colombia. For the record, one standard atmosphere of
1013.25hPa is equivalent to 760mmHg or 29.92inHg.
So where do the bar and the millibar units fit in? Well, the bar was a unit of weight used in the metric system before
about 1800. Then around 1890, it was used as a unit of atmospheric pressure by Norwegian physicist and pioneering
meteorologist Vilhelm Bjerknes. Since then, it has been used sporadically as a unit of atmospheric pressure, although
nowadays it is frowned upon and not regarded as part of the SI system of metric units.
For the record, 1 bar is regarded as equal to 100kPa or 1000hPa and 1mbar equal to 1hPa or 100Pa. Thus, a standard atmosphere corresponds to 1013.25mbar or 1.01325bar. For more information, see https://en.wikipedia.org/wiki/
Atmospheric_pressure
siliconchip.com.au
Celebrating 30 Years
December 2017 81
The GY-BM module shown above,
close to actual size.
Fig.8: complete circuit diagram for the GY-BM module. Compared to the GY-68's
circuit shown in Fig.2, this device is quite a bit simpler in design, removing the
need for an external regulator.
You’ll then see a list of observation stations in that area and then
when you click on a station near you,
you’ll see a list of the weather data
for that day, including temperature
and MSLP.
The new GY-BM module
Elecrow have recently added a second digital Barometer/Temperature
module to their range: the GY-BM
module, based on Bosch Sensortec’s
new BMP280 digital sensor IC.
The new module is only slightly
larger than the GY-68, but it is still
very small – measuring only 15 x 11 x
3mm. On the other hand, the BMP280
sensor IC itself is even smaller than
the BMP180, measuring only 2.0 x
2.5 x 0.95mm.
Despite this tiny size the BMP280
offers some advantages over the
BMP180. These include a dual-mode
SPI interface (modes “00” or “11”) in
addition to the I2C interface, higher
measurement resolution for both pressure (0.16Pa vs 1Pa) and temperature
(0.01°C vs 0.1°C), lower current consumption (2.7µA vs 12µA) and an internal software configurable IIR filter
to allow minimisation of short-term
air pressure disturbances.
In terms of absolute accuracy, the
BMP280 is essentially identical to the
BMP180. Pressure accuracy is ±1hPa
from 0-65°C, while the temperature
accuracy is ±0.5°C at 25°C and ±1.0°C
from 0-65°C.
The internals of the BMP280 appear to be very similar to those of
the BMP180 shown in Fig.1, apart
from it being provided with an SPI
The new GY-BM module is a tad larger than the previous GY-68 model and
the BMP280 has near identical performance to the BMP180.
82
Silicon Chip
Celebrating 30 Years
interface as well as the I2C interface.
The calibration parameters are again
stored in a 22-byte internal EEPROM/
NVM (non-volatile memory) during
manufacture.
The circuit of the GY-BM module
is shown in Fig.8, and as you can see
it’s even simpler than that of the GY68 module shown in Fig.2. That is because the GY-BM module is intended
to run only from a nominal 3.3V supply, and as a result it has no on-board
LDO (low dropout) regulator.
On the other hand, it has a sixpin connector (CON1) compared to
the four pins of the GY-68. The two
extra pins are required because the
optional SPI interface requires four
pins, compared to just two for the
I2C interface.
To connect the GY-BM module to
a micro using the I2C interface, the
SDA line should be connected to pin
6 of CON1, while the SCL line is connected to pin 3.
Additionally, the CSB pin (CON1
pin 5) should be left floating, so it’s
pulled high via the 10kW pullup resistor – this signals to the BMP280 that
the I2C interface is to be used.
Finally, pin 4 of CON1 can be used
to set the module’s I2C address, connecting it to ground to give it the same
"default" address as the BMP180, or
connecting it to VIN (+3.3V) to give it
a different address.
However, if you want to connect
the GY-BM module to a micro using a
standard four-wire SPI interface, the
SDI line should be connected to pin
6 of CON1, the SDO line to pin 4 of
CON1, the SCK line to pin 3 of CON1
and finally the CSB (Chip Select-bar)
line to pin 5 of CON1.
The GY-BM module should be just
as easy to use as the GY-68 module.
Just make sure that you connect its
supply input VIN (CON1 pin 1) to
+3.3V, not the +5V supply used for
the GY-68 module. Otherwise the
BMP280 chip may be irrevocably
SC
damaged.
siliconchip.com.au
It’s not long to
Christmas – (just 3
weeks or 25 days!)
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subscription? (Or even reward yourself if no-one else will!)
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just starting out, SILICON CHIP is the one magazine that they’ll want to read from
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6GHz+
Touchscreen
Frequency and
Period Counter
Having described our new 6GHz+ Touchscreen Frequency/Period Counter
in the first article (October) and then built and tested it (November), we
shall now show how to use it and explain what it can do. Apart from its
very wide frequency range, it offers outstanding accuracy.
Part 3: by Nicholas Vinen
A
went well, your unit should be operaa few small tweaks as the software has
ssuming you’ve managed to
tional. The rest of this article explains
been finalised.
source the components for
how to use the software and its touchThere is information shown in each
the Frequency Meter (most of
screen interface.
corner of the screen, plus the large frewhich are available from either the
quency/period display in the centre.
SILICON CHIP Online Shop or Digi-Key)
Main screen display
The frequency/period is auto-ranging
and successfully put it together, you
Pretty much all the functions of the
with frequency using units of mHz
can then program the Explore 100 with
Frequency Counter are available on
(millihertz, ie, 1/1000th of one hertz),
the software.
the one main screen, shown in Fig.5.
Hz, kHz, MHz or GHz and period havWe don’t supply the PIC32 pre-proThis is similar to the prototype screen
ing units of ps, ns, µs, ms or s.
grammed with the BASIC code beshown in the last two articles but with
You can switch between frequency
cause the Explore 100 provides a USB
and period disinterface that makes
play by touching
loading it quite easy.
the centre of the
The PIC32 which
screen.
is supplied in our ExChanging beplore 100 kit (or the
tween frequency
one from Rictech in
and period disNew Zealand) does
play does not afalready have the
fect the way the
MMBasic firmware
measurement is
loaded. So you just
being taken; both
need to connect it to
readings are calyour PC, download
culated based on
the software from
the number of
our website (free for
pulses received
subscribers) and load
from the referit into the Micromite
ence clock and
Plus chip.
the input signal
The procedures for
in a given period.
doing that, as well as
The frequency
setting up the LCD
is simply calcutouchscreen, were Fig.5: the default main screen, showing the frequency reading in large digits at
lated as Fin/Fref
given in last month’s the centre and various additional information below that, and in the corners of
while the period
article.
the display. To change the settings in the corners, it’s generally just a matter of
is Fref/Fin.
Assuming that all touching that area of the screen.
84
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Celebrating 30 Years
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Note that all settings, including this
one, are retained in Flash memory automatically so that the configuration
is retained for the next time the unit
is powered up.
Accuracy and precision
estimate display
Another indication of reading accuracy is the fact that the last couple of
decimal places in the reading may be
dimmed, indicating that they have a
degree of uncertainty and even with
a stable signal, you may see these digits fluctuate. If averaging is active then
over time, the reading will become
more certain and these digits will
become lighter. With a stable signal,
white digits should be quite stable.
these update rates by touching the
update line near the lower right-hand
corner of the screen.
The update rate is independent of
the averaging setting. Say you select
30s averaging with a 2s update rate.
You will get a reading after two seconds but it will only be based on two
seconds of data.
Then you will get a reading two seconds later which will be slightly more
accurate (and the accuracy and precision figures will reflect this).
The time span over which the signal
has averaged so far is shown in parentheses ( ) at the end of the Mode line.
The reading accuracy will continue to improve until the 30-second
mark, at which point the precision
and accuracy figures will not improve.
The reading will continue to change
though, representing the average signal frequency over a time “window”
spanning the last 30 seconds.
In other words, the displayed value
is a moving average.
If the signal frequency changes, you
would have to wait 30 seconds for
the new reading to be accurate. Alternatively, you can simply touch at
the end of the Mode line, where the
averaging time so far is displayed, to
reset it to zero and start the averaging
window anew.
To change the maximum window
(ie, averaging) time, simply touch
the left side of that line instead. This
will cycle through a series of different time values from one second up
to ten minutes.
To turn averaging
off, you can keep
pressing this until
you get back to the
“immediate” setting or alternative,
to save time, hold
your finger on the
Mode line for a couple of seconds.
Regardless of what is being displayed, the precision and accuracy
estimates are shown below. Precision indicates repeatability, ie, if you
Input switching
measured the same exact signal using
the same settings on two different ocThe current input is shown in the
casions, this is the maximum differlower left-hand corner of the screen
ence you could get between the two
and you can switch inputs simply
readings.
by touching it. Make sure you press
This relates to the stability of the
far enough down the screen that you
reference oscillator and how its frearen’t pressing the Mode line above;
quency changes over time and with
changing mode will be explained
temperature.
shortly.
It’s computed based on the reference
Mode switching is simple since it
clock tolerance and measurement pejust toggles between the SMB (high
riod and shown as both the parts per
frequency) input and the BNC (low fremillion/billion error and a frequency
quency) input. If you’re using averagor period uncertainty.
ing, it will reset when changing inputs.
When using averaging, the uncerThe SMB input impedance is fixed
tainty will drop over time until it
at 50Ω but the BNC input impedance
reaches a minimum value, once the
can be switched between 75Ω and
programmed averaging time period
about 1MΩ. This can be changed simhas passed.
ply by touching that part of the Mode
The accuracy shown automatically
line when the BNC input is selected
improves quite dramatically if you’re
and like the other settings, it is reusing GPS disciplining since this will
tained even when power is lost.
allow the unit to compensate almost
Update rate and averaging
entirely for long-term drift (since GPS
timekeeping is much more stable) and
The range of update rates has been
temperature drift will also be reduced
expanded to include one update every
(but not eliminated).
three, two or one second or five times
The accuracy figure is shown in a
per second. You can cycle through
similar manner
but this also takes
into account the
initial error in the
reference oscillator frequency.
This can be reduced if you have
a more accurate
reference source
to calibrate the
TXCO.
When using
GPS disciplining,
the accuracy figure will generally match the precision figure (or
come close) since
the accuracy provided by the GPS Fig.6: a similar display but this time with the output shown as a period rather
time signal is ex- than a frequency, and with averaging enabled. Most of the operation and
interaction with the unit is done via this screen.
cellent.
siliconchip.com.au
Celebrating 30 Years
Changing the
display
brightness
To change the
LCD backlight display brightness,
press and hold your
finger on the lower
right-hand corner of
the screen, where
the current brightness percentage is
December 2017 85
displayed. While still pressing on the
screen, swipe your finger up or right to
increase the brightness, or left or down
to decrease the brightness.
Because you’re starting in the lowerright corner, it’s easiest to swipe up to
increase and left to decrease. But if you
swipe up and increase the brightness
too much, you can go either down or
left to bring it back to the desired value.
Reducing the brightness to the minimum will drop power consumption
by around 200-250mA compared to
maximum brightness. The estimated
current drawn from the DC supply for
a given configuration is shown in the
upper-left corner of the screen.
Frequency reference calibration
There are three ways to do this. The
first is the simplest but needs to be
done with the case open and requires
an accurate frequency meter. It needs
to be more accurate than the one you
are calibrating, eg, around 1ppm or
±0.0001% accuracy or better.
Measure the frequency at pin 9 of
the Explore 100 header, relative to pin
1 (ground). Then press on the TCXO
frequency at upper-left and hold your
finger down for a couple of seconds,
then lift it.
A keypad will appear and you can
enter the precise TCXO frequency in
Hz.
It will then ask you for a second
figure, the accuracy of your frequency meter, in ppb (parts per billion).
1ppm = 1000ppb = 0.0001%. This is
used to provide the estimated precision and accuracy figures when making a measurement.
If you don’t know, abort entering
this number and the default value for
an uncalibrated TCXO will be used,
but the calibration itself will still be
performed.
The new figures will be stored and
displayed but you can recalibrate again
at a later date if necessary.
The second option can be done with
the case closed and all you need is an
accurate frequency source. For example, you could use the 10MHz reference output from another piece of test
equipment.
Make sure the TCXO frequency is set
to the default value of 16.368MHz; if
not, set it using the above procedure.
Feed the signal in and measure its
frequency with reasonably long averaging (eg, one minute). Take note of the
figure shown on the screen. Let’s call it
Fmeas and the expected frequency Fexact. Now perform the following calculation, with all values in Hz:
TCXO =
16368000 x Fexact / Fmeas
You can now program the resulting
figure in as the new measured TCXO
frequency using the procedure given
above. If you know the accuracy of
your reference signal frequency, enter
that in when prompted for the “ppb”
figure (in parts per billion).
The third method is a combination
of the above two methods and requires
a stable (but not necessarily accurate)
frequency source along with an accurate frequency meter.
You simply measure the frequency
of your signal source using the accurate meter, then feed that same signal
into your newly built Frequency Meter and measure it as stated immediately above.
You can then perform the same calculation, using the figure you got from
your known-accurate meter in place
of Fexact and the figure from your new
Meter as Fmeas. As before, the accuracy (ppb) figure should reflect the accuracy of the meter you’re using for
calibration.
The upper-left corner also shows the
TCXO frequency and measured CPU
(PIC32) operating frequency.
The latter is mainly for interest’s
sake. The CPU is typically operated
at 80MHz as a compromise between
screen update speed and power consumption/stability.
The PIC32 itself is perfectly stable at
higher speeds but we saw some display
glitches when driving the touchscreen
at faster rates (the LCD bus speed is
determined by the CPU clock rate).
The TCXO specified operates at a
nominal 16.368MHz and this will be
the default value at power-up. It can
change for two reasons: either you’ve
manually calibrated it (as described
GPS disciplining
below) or the GPS 1PPS signal has been
used to determine the actual TCXO
If you fit a GPS module, this is all
frequency. So when GPS disciplining
pretty much automatic. The PIC32
is available, the
should detect a
TCXO setting autovalid serial stream
matically updates
from the GPS unit
when necessary.
and display some
These changfigures in the upes are saved to
per-right corner
the PIC32’s Flash
of the screen. If
memory so that
not, check that you
the frequency can
haven’t transposed
be accurate the
the TX and RX pins
next time the unit
of the GPS unit or
is powered up bemade some other
fore it’s been runmistake with the
ning long enough
wiring. Check also
to get an accurate
that the power LED
reading of the GPS
on your GPS unit
time base.
is lit.
For manual caliMost
GPS
bration (eg, if you
units (including
have not fitted a
the recommendFig.7: using the on-screen keypad to calibrate the onboard oscillator for greater
GPS unit), you must accuracy. There are three different calibration methods given in the text, with
ed VK2828) also
first measure the the simplest involving measuring the oscillator frequency with a more accurate has an LED which
TCXO frequency.
flashes when it has
meter and then typing it in as shown here.
86
Silicon Chip
Celebrating 30 Years
siliconchip.com.au
a good satellite
inputs. You still
SILICON CHIP 6GHz+ Touchscreen Frequency/Period Meter
lock.
just need to substiTimestamp,Hz,Freq,PrecHz,AccHz,TCXO,Input,Imped,Mode,AvgSec,GPSSats,UTC,Date
If you’re gettute the units when
6239317,5260135255,5.26013526GHz,240,370,16367993,SMB,50,1,5,124837,03112017
ting some indireading the divided
6239817,5260134170,5.26013417GHz,230,360,16367993,SMB,50,1,5,124837,03112017
cation in the upoutput to get the ac6240317,5260134285,5.26013429GHz,220,350,16367993,SMB,50,1,5,124838,03112017
per-right corner
tual frequency.
6240817,5260133925,5.26013393GHz,210,340,16367993,SMB,50,1,5,124838,03112017
that the GPS unit
Note that while the
6241317,5260133910,5.26013391GHz,200,330,16367993,SMB,50,1,5,124839,03112017
has been detectaverage
frequency
6241817,5260133965,5.26013397GHz,200,330,16367993,SMB,50,1,5,124839,03112017
ed but you aren’t
produced
from the
6242317,5260133940,5.26013394GHz,195,325,16367993,SMB,50,1,5,124840,03112017
seeing a proper
reference
output
6242817,5260133995,5.26013400GHz,190,320,16367994,SMB,50,1,5,124840,03112017
fix (latitude, lonshould
be
very
ac6243317,5260133965,5.26013397GHz,190,320,16367994,SMB,50,1,5,124841,03112017
gitude, time, date,
curate, there could
Table 1: sample output from the unit over the serial console, captured with
etc) then you may
be some jitter bea terminal emulator. The result is in a CSV format so you can save, plot
need to move the
cause of the Pulse
and analyse it easily using standard software such as Microsoft Excel or
unit closer to a
Diffusion technique
LibreOffice/OpenOffice Calc.
window or conused to provide an
sider fitting a GPS module with an and leave it powered up for at least accurate division ratio. So it’s best to
external antenna.
half an hour to allow it to calibrate feed it to equipment with a reasonably
Note that it may take several min- the TCXO frequency to a reasonable long acquisition window (say at least
utes to get a lock even with a good sig- accuracy.
100ms) to get good results.
nal, especially if the GPS module has
If you’re only using it in short bursts
not been used for many days.
later, it may not have enough time to Serial output
Once a signal has been found, a cir- get a good lock and so doing this periOne feature we haven’t mentioned
cle is displayed which should flash at odically (eg, every couple of months) so far is that the measured frequency/
1Hz, concurrent with the 1PPS signal will help it continue to provide good period, TCXO oscillator frequency and
from the GPS unit. It will be red if a accuracy.
general configuration are also printed
satellite lock has not yet been achieved
to the serial console in CSV format.
Reference output
or green if it has.
So if you want to hook the MeOnce it’s green, the unit will start inAs stated in the earlier articles, the ter up to your PC, you can do so and
ternally “time stamping” each pulse. reference (BNC) output can produce capture/log/process the resulting data
If the lock remains good for at least a one of three signals: a fixed 1Hz or quite easily.
few minutes, the time stamps will be 1kHz reference signal, or a frequency
You can see the output of the unit in
used to improve the TCXO frequency that is equal to the measured frequency MMEdit’s “MMChat” window or you
and thus the reading accuracy and divided by 1000 (for the BNC input) or could use a serial console program
precision.
like Tera Term Pro to view and capture
1,000,000 (for the SMB input).
The length of time that the unit has
This varying division ratio is nec- this data. Set its baud rate to 115,200
had a good satellite lock is shown be- essary to keep the output frequency and make sure the correct COM port
low the latitude, longitude and alti- within reason at the upper end of the is selected. Make sure to close MMEdtude information (which are provided device’s measurement range and is it before launching Tera Term Pro so
merely for your curiosity).
shown on-screen when you switch that the COM port isn’t already in use.
Also, it’s imOnce captured, save
portant to realthe data to a CSV file
ise that the time
so you can open it latand date giver for analysis.
en are for UTC
Conclusion
(GMT).
They’re also
Despite all the preprovided for
vious explanation,
your reference;
this meter is quite
you need to
simple to use, espeknow your curcially if you are usrent local time
ing GPS disciplinzone offset to
ing since there is no
convert them to
need for manual calilocal time.
bration.
By the way,
All you need to do
we suggest once
is connect your signal
you get the Meup to one of its inputs,
ter up and runpower it up, select the
ning, you leave
appropriate input and
it in a location Fig.8: having entered the measured TCXO frequency, you also have the option
averaging time, then
of providing an accuracy figure to go along with it. This allows the unit to
with a good compute and display the new, better accuracy figure for any given reading.
wait a few seconds and
GPS signal lock Press the Save button and the new calibration figures will take effect.
read off the result. SC
siliconchip.com.au
Celebrating 30 Years
December 2017 87
SILICON
CHIP
.com.au/shop
ONLINESHOP
Looking for a specialised component to build that latest and greatest SILICON CHIP project? Maybe it’s the PCB you’re after?
Or a pre-programmed micro? Or some other hard-to-get “bit”? The chances are they are available direct from the SILICON CHIP ONLINESHOP.
As a service to readers, SILICON CHIP has established the ONLINESHOP. No, we’re not going into opposition with your normal suppliers –
this is a direct response to requests from readers who have found difficulty in obtaining specialised parts such as PCBs & micros.
•
•
•
•
•
PCBs are normally IN STOCK and ready for despatch when that month’s magazine goes on sale (you don’t have to wait for them to be made!).
Even if stock runs out (eg, for high demand), in most cases there will be no longer than a two-week wait.
One low p&p charge: $10 per order, regardless of how many boards or micros you order! (Australia only; overseas clients – email us for a postage quote).
Our PCBs are beautifully made, very high quality fibreglass boards with pre-tinned tracks, silk screen overlays and where applicable, solder masks.
Best of all, those boards with fancy cut-outs or edges are already cut out to the SILICON CHIP specifications – no messy blade work required!
HERE’S HOW TO ORDER:
4 Via the INTERNET (24 hours, 7 days): Log on to our secure website –
All prices are in AUSTRALIAN DOLLARS ($AU)
siliconchip.com.au, click on “SHOP” and follow the links
4 Via EMAIL (24 hours, 7 days): email silicon<at>siliconchip.com.au – Clearly tell us what you want and include your contact and credit card details
4 Via MAIL (24 hours, 7 days): PO Box 139, Collaroy NSW 2097. Clearly tell us what you want and include your contact and credit card details
4 Via PHONE (9am-5pm EADST, Mon-Fri): Call (02) 9939 3295 (INT 612 9939 3295) – have your order ready, including contact and credit card details!
YES! You can also order or renew your SILICON CHIP subscription via any of these methods as well!
PRE-PROGRAMMED MICROS
Price for any of these micros is just $15.00 each + $10 p&p per order#
As a service to readers, SILICON CHIP ONLINESHOP stocks microcontrollers and microprocessors used in new projects (from 2012 on) and
some selected older projects – pre-programmed and ready to fly!
Some micros from copyrighted and/or contributed projects may not be available.
PIC12F675-I/P
PIC16F1455-I/P
PIC16F1507-I/P
PIC16F88-E/P
PIC16F88-I/P
PIC16LF88-I/P
PIC16LF88-I/SO
PIC16LF1709-I/SO
PIC16F877A-I/P
UHF Remote Switch (Jan09), Ultrasonic Cleaner (Aug10),
Ultrasonic Anti-fouling (Sep10), Cricket/Frog (Jun12), Do Not Disturb (May13)
IR-to-UHF Converter (Jul13), UHF-to-IR Converter (Jul13)
PC Birdies *2 chips – $15 pair* (Aug13), Driveway Monitor Receiver (July15)
Hotel Safe Alarm (Jun16), 50A Battery Charger Controller (Nov16)
Kelvin the Cricket (Oct17)
Microbridge (May17)
Wideband Oxygen Sensor (Jun-Jul12)
Hi Energy Ignition (Nov/Dec12), Speedo Corrector (Sept13),
Auto Headlight Controller (Oct13), 10A 230V Motor Speed Controller (Feb14)
Automotive Sensor Modifier (Dec16)
Projector Speed (Apr11), Vox (Jun11), Ultrasonic Water Tank Level (Sep11)
Quizzical (Oct11), Ultra LD Preamp (Nov11), 10-Channel Remote Control
Receiver (Jun13), Revised 10-Channel Remote Control Receiver (Jul13)
Nicad/NiMH Burp Charger (Mar14), Remote Mains Timer (Nov14)
Driveway Monitor Transmitter (July15), Fingerprint Scanner (Nov15)
MPPT Lighting Charge Controller (Feb16), 50/60Hz Turntable Driver (May16)
Cyclic Pump Timer (Sep16), 60V 40A DC Motor Speed Controller (Jan17)
Pool Lap Counter (Mar17), Rapidbrake (Jul17)
Garbage Reminder (Jan13), Bellbird (Dec13), GPS Analog Clock Driver (Feb17)
LED Ladybird (Apr13)
Battery Cell Balancer (Mar16)
6-Digit GPS Clock (May-Jun09), Lab Digital Pot (Jul10), Semtest (Feb-May12)
PIC16F2550-I/SP
Batt Capacity Meter (Jun09), Intelligent Fan Controller (Jul10)
PIC18F4550-I/P
GPS Car Computer (Jan10), GPS Boat Computer (Oct10)
PIC32MX795F512H-80I/PT Maximite (Mar11), miniMaximite (Nov11), Colour Maximite (Sept/Oct12)
Touchscreen Audio Recorder (Jun/Jul 14)
PIC32MX170F256B-50I/SP Micromite Mk2 (Jan15) – also includes FREE 47F tantalum capacitor
Micromite LCD BackPack [either version] (Feb16), GPS Boat Computer (Apr16)
Micromite Super Clock (Jul16), Touchscreen Voltage/Current Ref (Oct-Dec16)
Micromite LCD BackPack V2 (May17), Deluxe eFuse (Aug17)
Micromite DDS for IF Alignment (Sept17), Touchscreen Altimeter (Dec17)
PIC32MX170F256B-I/SP
Low Frequency Distortion Analyser (Apr15)
PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Now with Mk2 Firmware at no extra cost)
PIC32MX250F128B-I/SP
GPS Tracker (Nov13), Micromite ASCII Video Terminal (Jul14)
PIC32MX470F512H-I/PT
Stereo Audio Delay/DSP (Nov13), Stereo Echo/Reverb (Feb 14)
Digital Effects Unit (Oct14)
PIC32MX470F512H-120/PT Micromite PLUS Explore 64 (Aug 16), Micromite Plus LCD BackPack (Nov16)
PIC32MX470F512L-120/PT Micromite PLUS Explore 100 (Sep-Oct16)
dsPIC33FJ128GP802-I/SP Digital Audio Signal Generator (Mar-May10), Digital Lighting Controller
(Oct-Dec10), SportSync (May11), Digital Audio Delay (Dec11)
Quizzical (Oct11), Ultra-LD Preamp (Nov11), LED Musicolor (Nov12)
dsPIC33FJ64MC802-E/P
Induction Motor Speed Controller (revised) (Aug13)
dsPIC33FJ128GP306-I/PT CLASSiC DAC (Feb-May 13)
ATTiny861
Thermometer/Thermostat (Mar10), Rudder Position Indicator (Jul11)
ATTiny2313
Remote-Controlled Timer (Aug10)
When ordering, be sure to nominate BOTH the micro required AND the project for which it must be programmed.
SPECIALISED COMPONENTS, HARD-TO-GET BITS, ETC
NEW THIS MONTH:
ALTIMETER/WEATHER STATION
(DEC 17)
- Micromite 2.8-inch LCD BackPack kit programmed for the Altimeter/Weather Station project $65.00
- GY-68 barometric pressure and temperature sensor module (with BMP180)
$5.00
- DHT22 temperature and humidity sensor module
$7.50
PARTS FOR THE 6GHz+ TOUCHSCREEN FREQUENCY COUNTER
Explore 100 kit (Cat SC3834; no LCD included)
one ERA-2SM+ & one ADCH-80A+ (Cat SC1167; two packs required)
(OCT 17)
$69.90
$15.00/pack
3-WAY ADJUSTABLE ACTIVE CROSSOVER
(SEPT 17)
set of laser-cut black acrylic case pieces $10.00
LOGGING DATA TO THE ‘NET USING ARDUINO
(SEPT 17)
WeMos D1 R2 board $12.50
DELUXE EFUSE PARTS
(AUG 17)
IPP80P03P4L04 P-channel mosfets $4.00 ec
BUK7909-75AIE 75V 120A N-channel SenseFet $7.50 ec
LT1490ACN8 dual op amp $7.50 ec
P&P – $10 Per order#
DDS MODULES
(APR 17)
AD9833 DDS module (with gain control) (for Micromite DDS) $25.00
AD9833 DDS module (no gain control) (El Cheapo Modules, Part 6) $15.00
POOL LAP COUNTER
(MAR 17)
two 70mm 7-segment high brightness blue displays plus logic-level Mosfet $17.50
laser-cut blue tinted lid, 152 x 90 x 3mm
$7.50
STATIONMASTER
(MAR 17)
Hard to get parts: DRV8871 IC, SMD 1µF capacitor and 100kW potentiometer with detent
$12.50
ULTRA LOW VOLTAGE LED FLASHER
(FEB 17)
kit including PCB and all SMD parts, LDR and blue LED
$12.50
SC200 AMPLIFIER MODULE
(JAN 17)
hard-to-get parts: Q8-Q16, D2-D4, 150pF/250V capacitor and five SMD resistors
$35.00
60V 40A DC MOTOR SPEED CONTROLLER
$35.00
(JAN 17)
hard-to-get parts: IC2, Q1, Q2 and D1
COMPUTER INTERFACE MODULES
(JAN 17)
(DEC 16)
MICROBRIDGE
TOUCHSCREEN VOLTAGE/CURRENT REFERENCE
MICROMITE LCD BACKPACK KIT (programmed to suit) PLUS UB1 Lid
LASER-CUT MATTE BLACK LID (to suit UB1 Jiffy Box)
MICROMITE LCD BACKPACK V2 – COMPLETE KIT
PASSIVE LINE TO PHONO INPUT CONVERTER - ALL SMD PARTS
(NOV 16)
ARDUINO MUSIC PLAYER/RECORDER
(JUL 17)
Geeetech Arduino MP3 shield $20.00
ARDUINO LC METER
(JUN 17)
1nF 1% MKP capacitor, 5mm lead spacing
$2.50
(MAY 17)
PCB plus all on-board parts including programmed microcontroller
(SMD ceramics for 10µF) $20.00
(MAY 17)
includes PCB, programmed micro, touchscreen LCD, laser-cut UB3 lid, mounting hardware,
SMD Mosfets for PWM backlight control and all other on-board parts $70.00
EFUSE
(APR 17)
two NIS5512 ICs plus one SUP53P06 $22.50
CP2102 USB-UART bridge
microSD card adaptor
$5.00
$2.50
SHORT FORM KIT with main PCB plus onboard parts (not including BackPack
module, jiffy box, power supply or wires/cables)
$70.00
$10.00
$99.00
$5.00
MICROMITE PLUS EXPLORE 100 *COMPLETE KIT (no LCD panel)* (SEP 16)
$69.90
(includes PCB, programmed micro and the hard-to-get bits including female headers, USB and microSD
sockets, crystal, etc but does not include the LCD panel)
THESE ARE ONLY THE MOST RECENT MICROS AND SPECIALISED COMPONENTS. FOR THE FULL LIST, SEE www.siliconchip.com.au/shop
*All items subect to availability. Prices valid for month of magazine issue only. All prices in Australian dollars and included GST where applicable. # P&P prices are within Australia. O’seas? Please email for a quote
12/17
PRINTED CIRCUIT BOARDS
NOTE: The listings below are for the PCB only – not a full kit. If you want a kit, contact the kit suppliers advertising in this issue.
For more unusual projects where kits are not available, some have specialised components available – see the list opposite.
NOTE: Not all PCBs are shown here due to space limits but the SILICON CHIP ONLINESHOP has boards going back to 2001 and beyond.
For a complete list of available PCBs, back issues, etc, go to siliconchip.com.au/shop Prices are PCBs only, NOT COMPLETE KITS!
PRINTED CIRCUIT BOARD TO SUIT PROJECT:
PUBLISHED:
PCB CODE:
Price:
HIGH ENERGY ELECTRONIC IGNITION SYSTEM
DEC 2012
05110121 $10.00
1.5kW INDUCTION MOTOR SPEED CONTROLLER (NEW V2 PCB)DEC 2012 10105122 $35.00
2.5GHz DIGITAL FREQUENCY METER – MAIN BOARD
JAN 2013
04111121 $35.00
2.5GHz DIGITAL FREQUENCY METER – DISPLAY BOARD
JAN 2013
04111122 $15.00
2.5GHz DIGITAL FREQUENCY METER – FRONT PANEL
JAN 2013
04111123 $45.00
SEISMOGRAPH MK2
FEB 2013
21102131 $20.00
MOBILE PHONE RING EXTENDER
FEB 2013
12110121 $10.00
GPS 1PPS TIMEBASE
FEB 2013
04103131 $10.00
LED TORCH DRIVER
MAR 2013
16102131
$5.00
CLASSiC DAC MAIN PCB
APR 2013
01102131 $40.00
CLASSiC DAC FRONT & REAR PANEL PCBs
APR 2013
01102132/3 $30.00
GPS USB TIMEBASE
APR 2013
04104131 $15.00
LED LADYBIRD
APR 2013
08103131
$5.00
CLASSiC-D 12V to ±35V DC/DC CONVERTER
MAY 2013
11104131 $15.00
DO NOT DISTURB
MAY 2013
12104131 $10.00
LF/HF UP-CONVERTER
JUN 2013
07106131 $10.00
10-CHANNEL REMOTE CONTROL RECEIVER
JUN 2013
15106131 $15.00
IR-TO-455MHz UHF TRANSCEIVER
JUN 2013
15106132
$7.50
“LUMP IN COAX” PORTABLE MIXER
JUN 2013
01106131 $15.00
L’IL PULSER MKII TRAIN CONTROLLER
JULY 2013
09107131 $15.00
L’IL PULSER MKII FRONT & REAR PANELS
JULY 2013
09107132/3 $20.00/set
REVISED 10 CHANNEL REMOTE CONTROL RECEIVER
JULY 2013
15106133 $15.00
INFRARED TO UHF CONVERTER
JULY 2013
15107131
$5.00
UHF TO INFRARED CONVERTER
JULY 2013
15107132 $10.00
IPOD CHARGER
AUG 2013
14108131
$5.00
PC BIRDIES
AUG 2013
08104131 $10.00
RF DETECTOR PROBE FOR DMMs
AUG 2013
04107131 $10.00
BATTERY LIFESAVER
SEPT 2013
11108131
$5.00
SPEEDO CORRECTOR
SEPT 2013
05109131 $10.00
SiDRADIO (INTEGRATED SDR) Main PCB
OCT 2013
06109131 $35.00
SiDRADIO (INTEGRATED SDR) Front & Rear Panels
OCT 2013
06109132/3 $25.00/pr
TINY TIM AMPLIFIER (same PCB as Headphone Amp [Sept11])OCT 2013
01309111
$20.00
AUTO CAR HEADLIGHT CONTROLLER
OCT 2013
03111131
$10.00
GPS TRACKER
NOV 2013
05112131
$15.00
STEREO AUDIO DELAY/DSP
NOV 2013
01110131
$15.00
BELLBIRD
DEC 2013
08112131
$10.00
PORTAPAL-D MAIN BOARDS
DEC 2013
01111131-3
$35.00/set
(for CLASSiC-D Amp board and CLASSiC-D DC/DC Converter board refer above [Nov 2012/May 2013])
LED Party Strobe (also suits Hot Wire Cutter [Dec 2010])
JAN 2014
16101141
$7.50
Bass Extender Mk2
JAN 2014
01112131
$15.00
Li’l Pulser Mk2 Revised
JAN 2014
09107134
$15.00
10A 230VAC MOTOR SPEED CONTROLLER
FEB 2014
10102141
$12.50
NICAD/NIMH BURP CHARGER
MAR 2014
14103141
$15.00
RUBIDIUM FREQ. STANDARD BREAKOUT BOARD
APR 2014
04105141
$10.00
USB/RS232C ADAPTOR
APR 2014
07103141
$5.00
MAINS FAN SPEED CONTROLLER
MAY 2014
10104141
$10.00
RGB LED STRIP DRIVER
MAY 2014
16105141
$10.00
HYBRID BENCH SUPPLY
MAY 2014
18104141
$20.00
2-WAY PASSIVE LOUDSPEAKER CROSSOVER
JUN 2014
01205141
$20.00
TOUCHSCREEN AUDIO RECORDER
JUL 2014
01105141
$12.50
THRESHOLD VOLTAGE SWITCH
JUL 2014
99106141
$10.00
MICROMITE ASCII VIDEO TERMINAL
JUL 2014
24107141
$7.50
FREQUENCY COUNTER ADD-ON
JUL 2014
04105141a/b $15.00
TEMPMASTER MK3
AUG 2014
21108141
$15.00
44-PIN MICROMITE
AUG 2014
24108141
$5.00
OPTO-THEREMIN MAIN BOARD
SEP 2014
23108141
$15.00
OPTO-THEREMIN PROXIMITY SENSOR BOARD
SEP 2014
23108142
$5.00
ACTIVE DIFFERENTIAL PROBE BOARDS
SEP 2014
04107141/2 $10/SET
MINI-D AMPLIFIER
SEP 2014
01110141
$5.00
COURTESY LIGHT DELAY
OCT 2014
05109141
$7.50
DIRECT INJECTION (D-I) BOX
OCT 2014
23109141
$5.00
DIGITAL EFFECTS UNIT
OCT 2014
01110131
$15.00
DUAL PHANTOM POWER SUPPLY
NOV 2014
18112141
$10.00
REMOTE MAINS TIMER
NOV 2014
19112141
$10.00
REMOTE MAINS TIMER PANEL/LID (BLUE)
NOV 2014
19112142
$15.00
ONE-CHIP AMPLIFIER
NOV 2014
01109141
$5.00
TDR DONGLE
DEC 2014
04112141
$5.00
MULTISPARK CDI FOR PERFORMANCE VEHICLES
DEC 2014
05112141
$10.00
CURRAWONG STEREO VALVE AMPLIFIER MAIN BOARD
DEC 2014
01111141
$50.00
CURRAWONG REMOTE CONTROL BOARD
DEC 2014
01111144
$5.00
CURRAWONG FRONT & REAR PANELS
DEC 2014
01111142/3 $30/set
CURRAWONG CLEAR ACRYLIC COVER
JAN 2015
- $25.00
ISOLATED HIGH VOLTAGE PROBE
JAN 2015
04108141
$10.00
SPARK ENERGY METER MAIN BOARD
FEB/MAR 2015
05101151
$10.00
SPARK ENERGY ZENER BOARD
FEB/MAR 2015
05101152
$10.00
SPARK ENERGY METER CALIBRATOR BOARD
FEB/MAR 2015
05101153
$5.00
APPLIANCE INSULATION TESTER
APR 2015
04103151
$10.00
APPLIANCE INSULATION TESTER FRONT PANEL
APR 2015
04103152
$10.00
LOW-FREQUENCY DISTORTION ANALYSER
APR 2015
04104151
$5.00
APPLIANCE EARTH LEAKAGE TESTER PCBs (2)
MAY 2015
04203151/2 $15.00
APPLIANCE EARTH LEAKAGE TESTER LID/PANEL
MAY 2015
04203153
$15.00
BALANCED INPUT ATTENUATOR MAIN PCB
MAY 2015
04105151
$15.00
PRINTED CIRCUIT BOARD TO SUIT PROJECT:
PUBLISHED:
BALANCED INPUT ATTENUATOR FRONT & REAR PANELS
4-OUTPUT UNIVERSAL ADJUSTABLE REGULATOR
SIGNAL INJECTOR & TRACER
PASSIVE RF PROBE
SIGNAL INJECTOR & TRACER SHIELD
BAD VIBES INFRASOUND SNOOPER
CHAMPION + PRE-CHAMPION
DRIVEWAY MONITOR TRANSMITTER PCB
DRIVEWAY MONITOR RECEIVER PCB
MINI USB SWITCHMODE REGULATOR
VOLTAGE/RESISTANCE/CURRENT REFERENCE
LED PARTY STROBE MK2
ULTRA-LD MK4 200W AMPLIFIER MODULE
9-CHANNEL REMOTE CONTROL RECEIVER
MINI USB SWITCHMODE REGULATOR MK2
2-WAY PASSIVE LOUDSPEAKER CROSSOVER
ULTRA LD AMPLIFIER POWER SUPPLY
ARDUINO USB ELECTROCARDIOGRAPH
FINGERPRINT SCANNER – SET OF TWO PCBS
LOUDSPEAKER PROTECTOR
LED CLOCK
SPEECH TIMER
TURNTABLE STROBE
CALIBRATED TURNTABLE STROBOSCOPE ETCHED DISC
VALVE STEREO PREAMPLIFIER – PCB
VALVE STEREO PREAMPLIFIER – CASE PARTS
QUICKBRAKE BRAKE LIGHT SPEEDUP
SOLAR MPPT CHARGER & LIGHTING CONTROLLER
MICROMITE LCD BACKPACK, 2.4-INCH VERSION
MICROMITE LCD BACKPACK, 2.8-INCH VERSION
BATTERY CELL BALANCER
DELTA THROTTLE TIMER
MICROWAVE LEAKAGE DETECTOR
FRIDGE/FREEZER ALARM
ARDUINO MULTIFUNCTION MEASUREMENT
PRECISION 50/60Hz TURNTABLE DRIVER
RASPBERRY PI TEMP SENSOR EXPANSION
100DB STEREO AUDIO LEVEL/VU METER
HOTEL SAFE ALARM
UNIVERSAL TEMPERATURE ALARM
BROWNOUT PROTECTOR MK2
8-DIGIT FREQUENCY METER
APPLIANCE ENERGY METER
MICROMITE PLUS EXPLORE 64
CYCLIC PUMP/MAINS TIMER
MICROMITE PLUS EXPLORE 100 (4 layer)
AUTOMOTIVE FAULT DETECTOR
MOSQUITO LURE
MICROPOWER LED FLASHER
MINI MICROPOWER LED FLASHER
50A BATTERY CHARGER CONTROLLER
PASSIVE LINE TO PHONO INPUT CONVERTER
MICROMITE PLUS LCD BACKPACK
AUTOMOTIVE SENSOR MODIFIER
TOUCHSCREEN VOLTAGE/CURRENT REFERENCE
SC200 AMPLIFIER MODULE
60V 40A DC MOTOR SPEED CON. CONTROL BOARD
60V 40A DC MOTOR SPEED CON. MOSFET BOARD
GPS SYNCHRONISED ANALOG CLOCK
ULTRA LOW VOLTAGE LED FLASHER
POOL LAP COUNTER
STATIONMASTER TRAIN CONTROLLER
EFUSE
SPRING REVERB
6GHz+ 1000:1 PRESCALER
MICROBRIDGE
MICROMITE LCD BACKPACK V2
10-OCTAVE STEREO GRAPHIC EQUALISER PCB
10-OCTAVE STEREO GRAPHIC EQUALISER FRONT PANEL
10-OCTAVE STEREO GRAPHIC EQUALISER CASE PIECES
RAPIDBRAKE
DELUXE EFUSE
DELUXE EFUSE UB1 LID
MAINS SUPPLY FOR BATTERY VALVES (INC. PANELS)
3-WAY ADJUSTABLE ACTIVE CROSSOVER
3-WAY ADJUSTABLE ACTIVE CROSSOVER PANELS
6GHz+ TOUCHSCREEN FREQUENCY COUNTER
KELVIN THE CRICKET
NEW THIS MONTH
6GHz+ FREQUENCY COUNTER CASE PIECES (SET)
SUPER-7 SUPERHET AM RADIO PCB
SUPER-7 SUPERHET AM RADIO CASE PIECES
MAY 2015
04105152/3
$20.00
MAY 2015
18105151
$5.00
JUNE 2015
04106151
$7.50
JUNE 2015
04106152
$2.50
JUNE 2015
04106153
$5.00
JUNE 2015
04104151
$5.00
JUNE 2015
01109121/2 $7.50
JULY 2015
15105151 $10.00
JULY 2015
15105152
$5.00
JULY 2015
18107151
$2.50
AUG 2015
04108151
$2.50
AUG 2015
16101141
$7.50
SEP 2015
01107151 $15.00
SEP 2015
1510815 $15.00
SEP 2015
18107152
$2.50
OCT 2015
01205141 $20.00
OCT 2015
01109111 $15.00
OCT 2015
07108151
$7.50
NOV 2015
03109151/2 $15.00
NOV 2015
01110151 $10.00
DEC 2015
19110151 $15.00
DEC 2015
19111151 $15.00
DEC 2015
04101161
$5.00
DEC 2015
04101162 $10.00
JAN 2016
01101161 $15.00
JAN 2016
01101162 $20.00
JAN 2016
05102161 $15.00
FEB/MAR 2016
16101161 $15.00
FEB/MAR 2016
07102121
$7.50
FEB/MAR 2016
07102122
$7.50
MAR 2016
11111151
$6.00
MAR 2016
05102161 $15.00
APR 2016
04103161
$5.00
APR 2016
03104161
$5.00
APR 2016
04116011/2 $15.00
MAY 2016
04104161 $15.00
MAY 2016
24104161
$5.00
JUN 2016
01104161 $15.00
JUN 2016
03106161
$5.00
JULY 2016
03105161
$5.00
JULY 2016
10107161 $10.00
AUG 2016
04105161
$10.00
AUG 2016
04116061
$15.00
AUG 2016
07108161
$5.00
SEPT 2016
10108161/2 $10.00/pair
SEPT 2016
07109161 $20.00
SEPT 2016
05109161 $10.00
OCT 2016
25110161
$5.00
OCT 2016
16109161
$5.00
OCT 2016
16109162
$2.50
NOV 2016
11111161 $10.00
NOV 2016
01111161
$5.00
NOV 2016
07110161
$7.50
DEC 2016
05111161 $10.00
DEC 2016
04110161 $12.50
JAN 2017
01108161 $10.00
JAN 2017
11112161 $10.00
JAN 2017
11112162 $12.50
FEB 2017
04202171 $10.00
FEB 2017
16110161
$2.50
MAR 2017
19102171 $15.00
MAR 2017
09103171/2 $15.00/set
APR 2017
04102171
$7.50
APR 2017
01104171 $12.50
MAY 2017
04112162
$7.50
MAY 2017
24104171
$2.50
MAY 2017
07104171
$7.50
JUN 2017
01105171 $12.50
JUN 2017
01105172 $15.00
JUN 2017 $15.00
JUL 2017
05105171 $10.00
AUG 2017
18106171 $15.00
AUG 2017
SC4316 $5.00
AUG 2017
18108171-4 $25.00
SEPT 2017
01108171 $20.00
SEPT 2017
01108172/3 $20.00/pair
OCT 2017
04110171 $10.00
OCT 2017
08109171 $10.00
PCB CODE:
Price:
DEC 2017 $15.00
DEC 2017
06111171 $25.00
DEC 2017 $20.00
LOOKING FOR TECHNICAL BOOKS? YOU’LL FIND THE COMPLETE LISTING OF ALL BOOKS AVAILABLE IN THE SILKS & DVDs” PAGES AT SILICONCHIP.COM.AU/SHOP
CIRCUIT NOTEBOOK
Interesting circuit ideas which we have checked but not built and tested. Contributions will be
paid for at standard rates. All submissions should include full name, address & phone number.
Four quadrant power supply is based on high voltage op amp
This circuit resembles an audio
power amplifier and indeed, it may be
used as one. But since it’s able to sink
or source a substantial current of up
to about 7A, at voltages up to around
±36V, it also makes a very handy power supply.
“Four-quadrant” indicates that it
can sink or source current with either
positive or negative output voltages.
It’s based around IC1, an OPA453
high-voltage op amp. This can operate
with supplies from ±10V up to ±40V.
Its output (pin 6) can supply up to
±50mA to the load at CON4 directly
via a 1kW resistor.
To increase the current capability,
this output pin also drives a complementary pair of Darlington emitter-followers formed by NPN transistors Q1/
90
Silicon Chip
Q3 and PNP transistors Q2/Q4.
Additional transistors Q5 and Q6
are effectively in parallel with Q3 and
Q4 respectively, and further boost the
output current capability.
It’s possible to parallel more sets of
transistors for higher output currents,
assuming the power supply has the capacity. If you only need a few amps,
you could omit Q5 and Q6 to save
money and space.
IC1 does not drive the base of Q1
and Q2 directly as this would cause
glitches in the output when switching
between sourcing and sinking current.
Instead, there is a base bias generating network consisting of small signal
diodes D1-D4, 10kW resistors between
these diodes and the supply rails, resistors R1 and R2 in parallel with D1-
Celebrating 30 Years
D4 and two 100µF capacitors, also
across the diode pairs.
Most of the time, current flows from
the VCC rail, through the upper 10kW
resistor, then through diodes D1-D4,
the second 10kW resistor and out
through the VEE negative rail. This
sets up a bias of around 1.2V across
D1 and D2 and a similar bias voltage
across D3 and D4.
The parallel 100µF capacitors are
charged up to this potential and this
helps preserves the bias for a short
time if the op amp output swings near
one of the rails.
In this case, the voltage across the
associated 10kW resistor will be very
low and so very little current will flow
through the bias network, hence the
need for these capacitors.
siliconchip.com.au
By shunting some current around
D1-D4, R1 and R2 reduce the bias voltage and it can be tweaked by varying
their values.
Lower values (<1kW) will give lower
quiescent current and higher values
will give higher quiescent current and
thus lower distortion for AC signals (to
a point). Be careful not to make the values too high or thermal runaway could
occur, damaging Q3-Q6.
The ~1.2V bias bases the base of Q1
to be around 1.2V above the op amp
output, and the base of Q2 around 1.2V
below the op amp output. This keeps
the base-emitter junctions of Q1-Q6
forward-biased with around 0.6V each,
causing a small quiescent current to
flow through all these devices.
This quiescent current flows through
the 300W emitter resistors for Q1 and
Q2, and the 0.22W emitter resistors
for Q3-Q6.
If the quiescent current increases,
therefore, the voltage across these
emitter resistors increases, reducing the base-emitter voltage of those
transistors and therefore reducing the
collector (and emitter) current. Thus
these resistors provide negative feedback to stabilise the quiescent current.
It is possible to operate the circuit
without the bias network, ie, remove
D1-D4, R1, R2 and the two 100µF capacitors.
However, the op amp output will
have to swing quickly between -1.4V
and +1.4V when it transitions between
sinking and sourcing current and so
the output will not be as clean. However, this will reduce standing power
consumption and dissipation in the
components .
A Zobel network across CON4, comprising a series 1W resistor and 100nF
capacitor, prevents oscillation due to
the phase shift caused by the output
buffer network. LED1 and LED2 are
connected anode-to-cathode so that
LED1 lights for a positive output voltage and LED2 for a negative voltage.
The brightness of these LEDs increases
with increasing output voltage.
CON3, the monitor output, is fed
with a signal that is attenuated by a
factor of 10 compared to the main output and is handy to feed to an oscilloscope for viewing.
The control signal is fed into CON1
and can come from an audio signal
source, potentiometer wiper, etc. For
DC control (eg, using this as a power
supply), S1 should be closed. The input impedance is 100kW.
Feedback from the output to inverting pin 2 of IC1 provides a gain of
ten. The minimum gain the OPA453
requires for stability is five. So if you
connect a pot across a ±5V regulated
supply and then feed the wiper signal
to CON1, this will allow you to vary
the output over the full ±37V (approximate) range. For AC use, the bandwidth is over 100kHz.
IC1 runs off the main VCC/VEE supply, however, it is decoupled using
two RC low-pass filters of 100W and
220µF. This prevents ripple and noise
from the main supply from affecting
the op amp.
The Flag output, at CON2, provides
a signal which indicates whether IC1
has shut down due to overheating.
Note that if you plan to use this feature to protect the unit against overheating, you would need to mount IC1
on the same heatsink as Q1-Q6, ideally
in the middle and close to these transistors, and even then there would be
no guarantee that it would trip before
Q1-Q6 fail. It depends on many factors
such as the gain of Q1-Q6.
IC1 comes in a 7-pin TO-220 package.
Petre Petrov,
Sofia, Bulgaria ($60)
Radio, Television & Hobbies: the COMPLETE archive on DVD
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Celebrating 30 Years
December 2017 91
Micromite-based Air Conditioner Remote Control
This circuit allows us to turn on our
upstairs air conditioner while we are
still downstairs, to cool the sleeping
area at night.
The air conditioner doesn’t need
to run all night; just long enough to
cool and dehumidify the bedroom (or
warm it up in winter). So the controller automatically turns it off either
when a target temperature has been
reached, or after a fixed delay, whichever comes first.
Our air conditioner has no remote
control, just a control panel on the wall
with an on/off button and some mode/
thermostat control buttons hidden beneath a flip-down panel.
We rang the distributor to inquire
about adding a remote control, however, all they offered was an expensive
infrared module which would only
work in line-of-sight. So we came up
with our own 315MHz smart radio
control circuit instead.
The circuit is based around a 28-pin
Micromite (PIC32MX170F256B) chip,
IC1. DS18B20 digital temperature sensor IC2 is connected to pin 14 with a
4.7kW pull-up/power supply resistor,
allowing IC1 to monitor the temperature near the control panel.
A commercial 315MHz four-channel
remote control receiver (shown below)
is connected to pins 15-18 and pulls
one of these low when one of the but-
tons on the associated remote (depicted) is pressed.
The LCD module shows the current
room temperature at all times and also
shows the remaining time and pre-set
temperature once the air conditioner
has been switched on.
It is connected in the usual way,
with Micromite pins 4-7 driving the
four-bit data bus (D4-D7) and pins
9 and 10 controlling the Enable and
Reset inputs respectively. A 10kW
resistor sets the backlight brightness
while a 1.8kW fixed resistor sets the
LCD contrast.
Pin 23 of the Micromite drives
a 4.5V (nominal) reed relay, RLY1,
which has its COM/NO contacts connected across the on/off pushbutton
in the aircon control panel.
To turn the air conditioner on or off
it simply pulses the relay for a short
time to simulate a button press. Since
the Micromite monitors the temperature, the only time we need to use the
control panel is to switch between the
heating and cooling modes.
Pressing button “A” on the remote
(pulling pin 15 of IC1 low) causes the
Micromite to turn the air conditioner
on, assuming that the ambient temperature is not already at the target. Once
the required temperature is reached,
or the maximum on-time has passed,
it will activate RLY1 again, switching
the aircon unit off.
Buttons “C” and “D” adjust the target temperature up or down. Pressing
these causes pin 17 or 18 of IC1 to be
pulled low. The micro has internal
pull-up currents enabled on these pins
which normally keeps them high (at
around 3.3V) but when the remote
control receiver pulls them down to
0V, IC1 senses this.
Pressing button “B” (pulling pin 16
of IC1 low) adjusts the maximum ontime. Initially, this is half an hour and
it increases by another half hour each
time button B is pressed. It is reset to
the initial half-hour time each time the
unit switches the air conditioner off.
If button “B” is held down for more
than three seconds, a menu is displayed on the LCD which allows you
to control whether the piezo sounder (driven from pin 26 of IC1) beeps
when the set temperature is reached
and when buttons on the remote are
pressed. This menu also lets you
change the duration of these beeps.
Power is from a 5V linear or switchmode supply and is reduced to 3.3V
for IC1 by an MCP1700 linear regulator. Finally, LED1 flashes when a remote control signal is received and
LK1 provides a method to disable the
temperature read-out on the LCD.
A PCB design is available for this
project and can be downloaded from
the Silicon Chip website. The corresponding parts list for building the
board is shown on the next page. Once
built, the board will fit inside a small
plastic box of 125 x 85 x 25mm.
Note that you can use a DHT22 temperature/humidity sensor in place of
the DS18B20, as shown in the overlay
diagram below. The software will then
display both temperature and humidity.
Two versions of the software are
available for download from the Silicon Chip website. “telecontrol V1_1.
bas” should be used if a DS18B20 sensor has been fitted while “telecontrol
V1_2.bas” is for use with the DHT22.
Gianni & Charmaine Pallotti,
North Rocks, NSW. ($90)
Right: PCB overlay
for the aircon remote
controller.
Below: the 315MHz
remote control, which
came along with a
matching receiver.
92
Silicon Chip
Celebrating 30 Years
siliconchip.com.au
The wires from
the 4.5V relay
are soldered in
parallel with the
power button
on the aircon,
denoted by the
red circle on
the photo. Not
all aircons will
have these pins
in the same
location.
Parts
1 single-sided PCB, code 06102171, 89 x 65mm
1 16x2 alphanumeric LCD screen
1 28-pin narrow DIL socket
1 4.5V DC coil reed relay (RLY1; AXICOM FX2 D3204 –
available from au.element14.com)
1 3-12V self-oscillating piezo buzzer
3 2-pin male headers (CON1-CON3)
1 16-pin female header (CON4)
1 3-pin female header (CON5)
1 2-pin header with shorting block (JP1)
1 4-way 315MHz remote control receiver with key-fob
transmitter
Semiconductors
1 PIC32MX170F256B programmed with Micromite
firmware (IC1)
1 DS18B20 digital temperature sensor (TO-92) (TS1) OR
1 DHT22/AM2302 temperature & humidity sensor (Silicon
Chip Online Shop Cat SC4150)
1 MCP1700-3.3 linear regulator (REG1)
1 5mm LED (LED1)
1 1N4004 1A diode (D1)
Capacitors
1 47µF 6V tantalum
2 10µF 16V electrolytic
1 100nF ceramic or MKT
The small receiver board for the remote is located at the
bottom of the PCB, with the 16-pin female header used
to connect a 16x2 LCD screen
siliconchip.com.au
Resistors (all 0.25W, 1%)
3 10kW
1 4.7kW
1 1.8kW
Celebrating 30 Years
1 330W
December 2017 93
Vintage Radio
By Marc Chick
Roberts R66 4-valve 2-band
Portable Superhet
Roberts is a British brand previously not often seen in Australia
although Roberts DAB+ radios have been on sale in recent times. In
essence, this is not a restoration story but a straightforward repair of
a set that was in fairly good condition.
The styling of the R66 portable is
interesting and apparently the inspiration for the design came from the
leatherette handbags owned by the
wife of Harry Roberts.
Interestingly, Roberts are now producing a range of retro DAB+/DAB/FM
radios with similar styling although
they are not available on the Australian market (see www.robertsradio.
com/uk/products/retro-radios).
Introduced in 1956, the Roberts R66
is 4-valve set which can be run from
230VAC mains or batteries. It was unusual in using selenium rectifiers for
the HT and LT (filament) supply rails
and it also employed a ferrite rod antenna at a time when most equivalent
Australian sets used a wound loop
antenna.
94
Silicon Chip
The four battery valves are unique
to European sets, having been manufactured at times by Philips, Mullard,
Siemens and Telefunken, but the circuit itself is a conventional superheterodyne with two bands: MW and LW.
The first valve is a DK96 pentagrid
converter which functions as a mixer-oscillator, commonly referred to
as a frequency changer. Its intermediate frequency is 470kHz; somewhat
higher than the 455kHz used in most
Australian sets. V1’s plate drives the
first IF transformer.
The ferrite rod antenna circuit’s
bandwidth is evidently wide enough
to tune both the MW and LW bands.
The oscillator circuit is switched to
cover the two bands using a large wafer switch.
Celebrating 30 Years
The secondary of the first IF transformer drives the grid of V2, a DF96
pentode and its plate, in turn, drives
the second IF transformer and this
drives the grid of V3, a DAF96 diodepentode which functions as the demodulator and audio preamplifier.
The audio signal from V3’s diode
appears across capacitor C19 is fed
via the volume potentiometer R8 to
the grid of V3. Its output is capacitively coupled to the grid of pentode
V4, operating as a class-A stage with
transformer T1 which drives the loudspeaker. There is no negative feedback,
probably because the circuit did not
have a lot of gain to spare.
The demodulated audio is also used
to apply AGC back to the input grid of
V1 and the control grid of V2.
siliconchip.com.au
Fig.1: complete circuit diagram for the Roberts R66 radio. In this circuit, switches denoted with an (M) close for mains operation, while those with the suffix (B)
close for battery operation, and are controlled by the leftmost knob on the radio. This knob also changes tuning over the MW or LW band, with switches S1, S3 & S5
closing for MW operation and S2 & S4 closing for LW. Image source: Radiomuseum (www.radiomuseum.org/r/roberts_r66r_6.html); from the service sheet.
The AC power supply uses selenium rectifiers as noted above. The HT
supply is a half-wave rectifier involving MR1 and capacitor C28 to produce
about 90V DC.
The filament supply is DC as well,
involving two selenium rectifiers,
MR2 & MR3 and three stages of filtering with resistors R15 & R16 and capacitors C29, C30 & C31. The resulting low ripple supply is essential for
filaments (cathodes) of these battery
valves, otherwise hum would be a serious problem when operating from
the mains supply.
This particular radio had apparently
come from the UK to Australia, after
a long stint in South Africa. While it
needed some repairs, its overall appearance was not bad for such a traveller although the leatherette covering
was coming off in a number of places and the carrying strap was quite
frayed. The leatherette was glued back
as necessary but that was the extent of
any cosmetic repairs.
Note that the dial on this Roberts set
looks a little odd since it reads in metres rather than kHz. Hence the medium wave (MW) band ranges from 182
to 590m (or 508kHz to 1.68MHz) while
the long wave (LW) band ranges from
900 to 2000m (150kHz to 333kHz).
In spite of its generally good appearance, any temptation to just power it
up was resisted and the chassis was
carefully inspected. One should always carefully inspect a radio foreign
to you (not because it’s foreign) and of
unknown provenance.
There are often hidden dangers lurking, for those who fail to look. Never
forget that most of these old radios
were dumped when they had failed
and were replaced with something
Electrolytic capacitor C30 is
shown above with a leak that
solidified on the top of its can.
siliconchip.com.au
Celebrating 30 Years
December 2017 95
Shown above is the radio seated in its upright “playing”
position. The speaker is located behind the grille, as
shown in the photo to the right.
The radio can run from either 200-250VAC mains or two
dry batteries, one rated at 90V for HT and the other at
1.5V for LT.
much more modern, probably transistorised.
So I looked for any obvious tampering within the chassis, as well as
the wire insulation quality. Then the
mains and speaker transformers were
checked. C30, one of the large electrolytic capacitors was leaking from the
top of the can, so that was an immediate visual inspection fail. So powering
up the radio was out of the question.
That capacitor and its mates, C29
& C31, all 2500µF 3V rated, were replaced and so were the rest of the electrolytics apart from C27 & C28 which
was a twin capacitor (ie, two capacitors in one can).
They were checked for leakage and
much to my surprise, they were comparable after a few minutes at 150V to
a new 47µF 450V capacitor, drawing
less than 1mA, so it was reconnected.
The HT current is listed at 10.4mA.
All the ceramic capacitors were
fine but some of the resistors were
replaced. Capacitor C14 (0.5µF paper) was lifted and tested at the closest voltage to its rating (350V DC) as I
could apply with one of my insulation
testers (250V DC). That gave a result
of 700kW and so it was more of a resistor than a capacitor.
That would have the effect of shunting away the AGC signal which would
otherwise be applied to the signal grid
96
Silicon Chip
of V1 (DK96) and also to the grid of
V2 (DF96).
In addition, in sets like this, the control grids draw insignificant current
and any leakage of positive voltage in
coupling to the grid from a plate will
impinge significantly on the bias. Anyway, the capacitor was replaced with a
modern plastic dielectric type.
Powering up
I noted before powering it that it
had 230VAC mains switching via wafer switches. Often that is a bad idea
but at least with this set both Neutral
and Active are switched separately
Opening the plywood case of the Roberts R66 shows the “top” of the chassis,
including the ferrite rod antenna. L1 & L2 form the ferrite road antenna coils
and are tuned via C3 as shown in Fig.1. The red/black wire is for the HT battery
connections, while the yellow/green wire is for LT.
Celebrating 30 Years
siliconchip.com.au
Shown left is
the “bottom”
of the chassis
before
restoration
work had
begun. Since
the speaker is
attached to the
case, its leads
need to be
desoldered to
completely free
the chassis.
(ie, with a double-pole switch). The
switching also provides for changeover to battery power.
The circuit diagram reveals that because the set uses battery valves, with
directly heated cathodes, it is important that the filament supply has the
correct polarity since it forms part of
their grid bias. So one always needs to
check to see that things have not been
changed on this point.
Ultimately, after all the checks and
component replacements had been
completed, the set powered up without problems. Then it was on to check
the alignment.
It would be folly to assume that the
alignment would not have changed
after 60 over years, and so it had. The
MW coil had slipped on the aerial rod
and both bands were out of calibration.
They were re-adjusted to the manufacturer’s specifications. Its performance
is quite impressive.
SC
The underside
of the chassis
after repair,
with the
replacement
capacitors in
place. All the
electrolytic
capacitors,
except for
twin capacitor
C27/28, were
replaced.
All ceramic
capacitors
checked out
OK and only
a few resistors
needed to be
replaced.
siliconchip.com.au
Celebrating 30 Years
December 2017 97
ASK SILICON CHIP
Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line
and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au
Energy Meter required
to monitor whole house
Have you published an article on an
Energy Meter that can be installed into
the meter box which can log usage?
I am considering PV panels and/
or some sort of battery system for my
home but I’d like to calculate the economics of the exercise – I am not motivated by the feel-good factor.
Without a more detailed breakdown
of my home’s electricity usage (hourly), it isn’t possible to know whether
there is an economic benefit of installing panels or batteries. I have plenty
of north-facing roof space with a high
pitched roof which would be an ideal
place to install panels.
The new WA government is discussing an end of government subsidy to Synergy (the state-owned electricity retailer) that allows them to
sell electricity to the market (voters)
below cost. This could see WA electricity prices rising about 15% in the
short term.
With the falling prices of panels and
storage solutions coupled with the rise
in electricity supply costs, I believe
that the economic benefit is becoming
greater, although it probably still isn’t
economic when the life of the panels
and batteries is considered.
I guess if I get desperate I could
install a camera in the meter box to
photograph the meter every 60 minutes and OCR the pictures! (W. H., Mt
Pleasant, WA)
• Our latest Energy Meter, published
in August-October 2016, is designed to
monitor a power point and is rated at
20A. It is not suitable to monitor the
entire meter box. For more information on this see siliconchip.com.au/
Series/302 (errata, November 2016:
siliconchip.com.au/Article/10441).
Charging a gel cell
(SLA) battery
I have a caravan that has a 120W solar panel charging a 100Ah deep-cycle
battery. The caravan also has a small98
Silicon Chip
er 7Ah gel cell battery for emergency
braking, should the van and vehicle
disconnect.
A release cable pulls a switch that
applies power to the electric brakes.
This battery last for approximately 15
minutes. This battery receives some
charge from the vehicle whilst towing and can have an AC adaptor connected to charge whilst the van is connected to power.
My problem is that I don’t tow it long
enough or its not connected to power
and so it doesn’t keep this smaller battery charged. I have assembled a small
buck/boost module to provide 13.513.8V to charge the 7Ah battery from the
main battery. There is some electronics
in the battery box, including a diode to
prevent reverse flow. My questions are:
1) Is providing 13.5-13.8V continuously to the battery the best solution?
2) Should I just connect the main
battery to the smaller one via the
electronics and reverse flow diode?
3) Could I add another solar charge
controller just for this smaller battery?
(G. H., Littlehampton, SA)
• It really depends on the buck/boost
module and the amount of current this
can deliver to the 7Ah battery as to
whether it should be directly connected.
If you limit to a 1A charge then a
2.7W 10W resistor could be used to
restrict charging should the main battery be discharged. The resistor should
be inside a diecast box used as a heatsink, with wires exiting through a cable gland.
Having the buck/boost module powered from the solar panel and connected continuously to the 7Ah battery should be OK as charging current
will drop to a trickle once the battery
voltage reaches the buck/boost module output voltage.
Having the buck-boost module connected to the main vehicle battery is
probably not ideal as it will discharge
the main vehicle battery when it is not
being topped up via solar power or vehicle engine charging.
Celebrating 30 Years
You could add another charger for
the 7Ah battery but what you have
with the buck/boost module seems
adequate.
LK6 in Currawong
Stereo Valve Amplifier
I never got my Currawong up and
flying when I built it two years ago and
just the other day started fault finding.
I discovered that the 100µF capacitor
in the power-on delay circuit had high
leakage and managed to fix it.
However, there is one thing that
puzzles me. When looking at the schematic, LK6 actually shorts out one of
the diodes in BR1 that supplies the
12AX7s with heater current. I have no
plan other than to go without the link,
but what is it for?
I also checked the modifications proposed in parts 2 and 3 of Currawong
articles but cannot remember seeing
something out of the ordinary. And
I made all mods proposed. (M. K.,
Vänersborg, Sweden)
• There was a special note about LK6
on page 38 of the November 2014 issue. LK6 must not be fitted unless two
separate 12V transformer windings are
used, one to power the 6L6 heaters
(between pins 1 and 3 of CON8) and
one to power the 12AX7 heaters and
power-on delay/headphone relay circuity (connected between pins 4 and
5 of CON8).
In that case, fitting LK6 connects Vee
to ground and will not short out BR1.
See the October 2016 issue on pages
44-48, where we used this arrangement with a custom-wound transformer from Altronics which had the
required extra windings. You can preview this article at: siliconchip.com.
au/Article/10298
Retaining trigger output
in DDS IF Alignment
I have a query regarding the Touchscreen DDS IF Alignment module in
the September 2017 issue (siliconchip.
com.au/Article/10799).
siliconchip.com.au
Circuit Ideas Wanted
Got an interesting original circuit that you have cleverly devised? We need it and will pay good money to feature it in the
Circuit Notebook pages. We can pay you by electronic funds transfer, cheque (what are they?) or direct to your PayPal
account. Or you can use the funds to purchase anything from the SILICON CHIP on-line shop, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au
I have upgraded from the original
DDS generator published in April 2017
and have kept the trigger output on the
box. Does the upgraded software still
use this trigger output or has it been
disabled as it is no longer necessary?
(M. McC., Kelvin Grove, Qld)
• To avoid the need for having separate connectors for the IF alignment
detector input and trigger output, the
DDS IF Alignment unit was designed
to use the same pin (pin 24) as both
the analog input for IF alignment and
trigger output in the other modes. This
was not mentioned in the article.
Since you already have both connectors, it would be possible to modify
the software to use the original trigger output pin (pin 16) and use pin
24 as a dedicated analog input for IF
alignment.
We have modified the BASIC code
to allow this but have not tested it. If
any readers want to try this, they can
send us an email and we will supply
this modified code.
Ignition system needed
for Yamaha Jetski
I have a 1989 Yamaha WR500 twincylinder jetski. I am in need of a HighEnergy Electronic Ignition for it. The
original capacitor discharge ignition
(CDI) boxes are not available anymore.
Can you help me? (K. S., via email)
• We have published many ignition
systems in the past. The most recent
are listed below. Which one is suitable
depends on the way the original ignition was powered.
Some CDIs have a high-voltage generator coil incorporated in the generator and this type of ignition may be
replaced with the May 2008 Replacement CDI Module in most cases.
If the CDI was powered from the
12V supply then the High-Energy
Ignition from November and December
2012 or the CDI from December 2014
and January 2015 would be suitable.
These can be triggered by the reluctor,
Hall effect or points or optical pickups.
Note that many twin engines fire
siliconchip.com.au
both cylinders at once, so only one
ignition system is required. This is
a wasted spark system meaning that
when one cylinder is fired on the compression stroke, the other cylinder
spark is “wasted”, as it is not at the
right stage for firing (either the cylinder is near its lower position with
a two-stroke, or at the exhaust stroke
in a four-stroke).
■ December 2014 & January 2015:
High-Energy Multi-Spark CDI For
Performance Cars by John Clarke,
PCB code 05112141 (available from
the Silicon Chip online shop); see
siliconchip.com.au/Series/279
■ November & December 2012:
High-Energy Ignition System for
Cars by John Clarke, kits: Jaycar
KC5513 & Altronics K4030, PCB
code 05110121 (available from
the Silicon Chip online shop); see
siliconchip.com.au/Series/18
■ May 2008: Replacement CDI Module for Small Petrol Motors by John
Clarke, kits: Jaycar KC5466, PCB
code 05105081 (available from
Silicon Chip online shop); see
siliconchip.com.au/Article/1820
Sourcing 8-gang pots for
3-Way Active Crossover
Firstly, I wanted to say thanks for the
PCB and panels for the Active Crossover from the September and October issues (siliconchip.com.au/Series/318),
which all arrived.
I am starting to compile the components and am having a problem
trying to order the Bourns PTD90 potentiometers.
If I try to enter the full part number from the parts list in your article,
the Bourns website says no results. It
will show the correct looking pot if
I just enter PTD90 but requires a lot
more info to input in order to get the
right one.
Is it possible the part number in your
parts list is incorrect? (D. Y., Nelson,
NZ)
• The part number given is correct although it may be written
Celebrating 30 Years
PTD908-1015F-B103 (ie, with two
added dashes) and that may be why
the search was coming up blank. We
sell a pack of these pots with knobs in
our Online Shop, at siliconchip.com.
au/Shop/7/4408
They are also available from Mouser;
see siliconchip.com.au/link/aag9
Ultrasonic Anti-Fouling
with leaky capacitor
I built the two-channel version of
the Ultrasonic Anti-Fouling for Boats
Mk2 from the Jaycar kit (KC5535),
based on the project published in the
May and June 2017 issues (siliconchip.
com.au/Series/312). I have not yet installed it in my boat as there is an issue with starting the unit.
When first switched on, the green
LED comes on for about two seconds,
then the fault LED flashes and remains
in this state indefinitely. If I turn the
power off, wait until the fault LED
stops flashing and then turn the power
on, the unit runs as it should.
Even with a delay of around 20-30
minutes, it starts fine. But if I leave
the unit off for a longer time (an hour
or so), it reverts to the fault condition.
Whilst running, I have set up and
checked the under-voltage lockout
threshold and hysteresis. It all works
as it should.
I am quite an experienced electronics builder and have fully checked
that I have not placed any components wrongly, bad solder joints etc.
Once started, the unit runs perfectly
and I have had it run for days. Do you
have any solution for me? (D. B., Sydney, NSW)
• It seems that the unit has excessive leakage with one (or both) of the
low-ESR 2200µF capacitors, during
the soft start sequence. The leakage
will be more apparent when switching on the power after the capacitors
have fully discharged, ie, after it has
been off for a while.
To verify this, remove one capacitor
and check if the circuit starts up. If it
does, then the one which was removed
December 2017 99
Can IF Alignment project be use for FM receiver alignment
I have a question regarding your
455kHz DDS IF Alignment project
which was published in the September 2017 issue (siliconchip.com.au/
Article/10799).
I checked the original Touchscreen DDS Signal Generator article that the project was based on
(in the April 2017 issue) and it says
it can create sinewaves to 10MHz.
Would it be possible to set this up
for 10.7MHz IF alignment as well as
455kHz? (J. G., Mt Helen, Vic)
• It could work in theory but the
software as provided does not alis leaky. If not, try removing the other
one and see if it starts then. Replacing
the capacitor(s) should allow the unit
to start normally.
If you are prepared to still use the
leaky capacitor(s), you could add a resistor across the drain and source of Q5
to counteract the leakage so the circuit
will start up even after the capacitors
have fully discharged. A 330W 1W resistor should do the trick.
Programming
EEPROMs
Could the Microbridge (May 2017;
siliconchip.com.au/Article/10648) be
used with an adaptor to program EEPROMs? If yes, will pic32prog do the
job, or what program would you recommend? I need to burn an A25L80P
chip for a PC motherboard. (I. T., Blacktown, NSW)
• pic32prog is only designed for programming PIC32 chips. The easiest
way to program EEPROMs is to buy a
TL866CS programmer. They’re only
about $45 including postage. A25L80P
is listed among its supported chips.
Just do a google search for TL866CS
and you’ll find plenty of sellers on
eBay and AliExpress.
A correspondent who is
very new to electronics
Hello! I recently purchased the Digital Audio Delay kit (KC5506) from Jaycar, which was published in your December 2011 issue (siliconchip.com.
au/Article/1235) and I’m told you’re
the people to ask advice from. I hope
that’s true!
100
Silicon Chip
low it. The DDS module’s clock
runs at 25MHz so it should be capable of generating sinewaves up
to 12.5MHz. In practice, distortion
is already pretty high at 10MHz and
climbs above that.
However, this may not be a major issue for IF alignment since the
harmonics will be well outside the
IF bandwidth.
The main obstacle is that the original signal generator code from Geoff
Graham, which we used as a basis
for the IF Alignment project, has a
built-in limit of 10MHz.
When I bought the kit a couple of
weeks ago, I thought there’d be a small
amount of soldering – I had no idea it
would be as intense as it is. I’m fine
at soldering but lost when it comes to
electronics.
So I decided I could put together
the majority of it simply by copying
the overhead view picture of the completed PCB in the instruction pages.
This has been fine so far, except it’s
an average quality black-and-white reproduction so sometimes it’s hard to
see things. This is where I need advice.
The ICs seem to have matching “riser
pads” underneath (I’m sure this is the
wrong terminology). For instance, IC5
(74HC00) and the two nearby chips,
IC3 and IC4.
I found the actual ICs in the kit but
there are other pieces which exactly
match their outline and which seem
to fit together. But I see nothing about
them in the instructions and the photo
and diagram don’t show them.
If they are supposed to fit together,
do they need to be soldered together,
or are they just supposed to click together? The same goes for all the other ICs as they all seem to have matching risers.
I have another question about identifying a part. There’s an area with the
labels “5V” and “3.3V”, with “LK1”
nearby too – the area is allocated three
holes. The images and info in the plans
just isn’t enough for me to be confident
I’ve got the correct piece.
I’ve found one part in the kit which
is a strip of black plastic with three
pins through it. Is that the right part?
Which way up does it go – with the
long legs upright, or the short legs upCelebrating 30 Years
This seems to mainly be due to
the number of digits displayed in
the frequency field.
You could change the provided
code by searching for all instances of “9999999” (ie, 9.999999MHz,
the maximum) and change them to
“10999999”.
This may allow you to set a centre
frequency of 10.7MHz but we suspect the display would be wrong (the
top digit could be cut off).
Still, it might be worth a try. It
could possibly be made to work with
a little extra software tweaking.
right? I’m sorry I’m so terrible at terminology.
I hope I make some semblance of
sense. Thanks in advance for being
gentle with me! (S. J., via email)
• The parts you are asking about in
your first question are the IC sockets.
They are mentioned in the instructions
in the third paragraph under the heading “Through-hole parts” (on page 36
of our December 2011 issue).
You solder the sockets to the PCB,
with the notches in the same position
as the notches shown in the chips in
the overlay diagram, Fig.6.
Then, once you’ve finished soldering everything, you straighten the pins
of the ICs (either using a special tool
you can buy at Jaycar or using longnose pliers) and push them into the
sockets.
The sockets are a tight fit so they
hold the chips in place and form good
electrical contacts but you can still remove them later if you need to. It just
takes a bit of pulling.
The main thing to be careful of when
plugging the chips into their sockets
is to ensure that none of the legs get
folded up under the chip when you’re
pushing it into the socket.
And if you do remove them, you
need to pull evenly at either end to
avoid bending the pins (you can also
get a special puller tool to do this
which we recommend you use).
The likely source of your confusion
is that we don’t show the sockets in
Fig.6. This is done for two reasons:
one, because it would clutter up the
diagram and two, because you can
solder the ICs straight to the board if
you want to.
siliconchip.com.au
That does improve long-term reliability but makes it very difficult to
remove a chip if it goes bad, or if it’s
soldered the wrong way around, or if
two are swapped etc.
Regarding your second question,
that is the correct part and it’s a threepin male header. This is soldered to
the board with the long pins sticking up and the short pins through the
holes. Once in place, you can then
plug a shorting block (which should
also have been supplied) across two
of the three pins.
Depending on which two you
bridge, this selects either a 3.3V or
5V supply for the TOSLINK receivers. The labels on the board indicate
which end to insert the jumper for either supply option.
Varying Pre-champ
gain
I recently purchased the Jaycar
Pre-champ Preamplifier kit (KC5166)
based on the article from July 1994. I’m
using it to boost the output signal of
my guitar pickups, so I have inserted
it after the volume pot.
Which resistor can I replace with a
trimpot to reduce the amplification so
the signal coming out isn’t so “hot”?
I need some control over the output
impedance, otherwise, it clips most
interfaces or amps I use it with. It is a
killer little design and works perfectly
for my application because it doesn’t
colour the tone.
Or do you have some other suggestion of a design that would suit my purpose that you currently make? I want
something active that will run from a
9V battery. (J. R., via email)
• The 2.2kW resistor between the emitter of Q1 and collector of Q2 can be replaced with a 2kW trimpot, connected
as a rheostat (variable resistor), to vary
the gain. Alternatively, you could connect a 1kW trimpot in series with the
100W resistor, again wired as a rheostat.
How to program
various micros
I have been programming PICs and
PICAXE chips with a Windows 98
computer which has now died. I tried
using Google to find another way to
program them as I couldn’t get the software to work in Windows XP.
There’s so much stuff out there that
I really don’t know what’s best for me.
siliconchip.com.au
Charging LiFePO4 cells
The article by Jim Rowe in the
August 2017 issue on Li-ion batteries and chargers (siliconchip.com.
au/Article/10763) was informative,
but I prefer LiFePO4 cells for several reasons including improved
safety and the fact that the operating voltage range matches perfectly
the Micromite.
Are you going to do a similar article on low-power chargers for LiFePO4 cells? (A. B., Manly, Qld)
• LiFePO4 cells are very similar to
other Li-ion cells except for the fact
that they use LiFePO4 as the cathode material. Different cathode materials were discussed, if briefly, in
the article you refer to.
I’m a retired dabbler and only have basic computer knowledge. Could you
please suggest a device I could use.
(G. A., Salisbury Downs, SA)
• As you have found, it is quite difficult to program micros using old Windows computers. It does not matter
whether you want to dabble in micros
or devices such as Arduino, Raspberry
Pi or our Micromite, you are still going to need a much more recent model
computer.
For the long term, you probably
should consider a newer Windows machine – perhaps a secondhand laptop.
We use the PICkit 3 to program PICs,
either via an in-circuit serial programming (ICSP) header or using our PIC/
AVR Programming Adaptor Board design which was published in the May
and June 2012 issues (siliconchip.com.
au/Series/24). We also sometimes use a
TL866a “MiniPro” programmer which
can program almost any chip. It has a
40-pin ZIF socket and is supplied with
Windows software.
For programming PICAXEs, we normally use the official PICAXE USB
programming cable which is available
from Altronics (Cat Z6198).
Crazy cricket is not
quite right
I have built a number of these fun
kits as published in the June 2012 issue
(siliconchip.com.au/Article/638) and
they all work properly as designed.
However, one unit has a curious fault
in that the life of its CR2032 battery
Celebrating 30 Years
LiFePO4 cells can be charged in the
same way, using the CC-then-CV protocol. The only real difference is that
the CC charging current should be restricted to 0.5C and the switch to CV
charging made when the cell voltage
rises to 4.0V; the cell voltage should
not be allowed to rise beyond 4.2V.
Many low-cost lithium battery
chargers do provide for charging
LiFePO4 batteries while others could
probably be modified to meet these
requirements.
We published an article on this
technology in the June 2013 issue, titled “Get a LiFe with LiFePO4 Cells”.
You can see a preview at siliconchip.
com.au/Article/3816
is very short before becoming essentially flat, yet the other units have a
good long life.
The only modifications that I’ve
done is to replace the red LEDs with
blue LEDs.
Can anyone offer any ideas as to
why one unit has such a high current
drain? I have extensively gone over
both boards and there are no errors,
and all components are correct. Could
the PIC itself be causing the problem?
(F. S., Ingham, Qld)
• Make sure the PIC12F675 is programmed correctly with the fuses in
the Program Configuration Register as
shown here:
__CONFIG _CPD_OFF & _CP_
OFF & _BODEN_OFF & _
MCLRE_OFF & _PWRTE_ON
& _WDT_ON & _INTRC_OSC_
NOCLKOUT
There could be a short on the PCB
causing the high current or leakage
due to a contaminated PCB such as
oils or fluids spilt on the PCB. Give it
a good clean with methylated spirits
and see if that helps. Other problems
could be with the PIC12F675 itself; it
might have an internal fault causing
a high current drain.
GPS-Based Frequency
Reference queries
I am planning to construct the GPSBased Frequency Reference from the
March and April 2007 issues, with
improvements published in the May
December 2017 101
Library problem compiling Arduino Data Logger sketch
I am building the Arduino Data
Logger from the August and September issues (siliconchip.com.au/
Series/316). Thank you for another
interesting project.
I have finished the shield PCB so I
downloaded the latest Arduino IDE
1.8.4 and downloaded the Arduino
Data Logger software v1.0.
I unzipped the download and
there were two directories: sketch
and libraries. I loaded the six library
zip files and then opened the sketch
2007 and September 2011 issues
(siliconchip.com.au/Series/57). My
question is whether it is possible to
use a different GPS receiver module
than the one specified.
I have one u-blox Neo-7M module
and one VK2828U7G5LF module.
Before building the PCB I loaded the
HEX file (GPSFrqv3.HEX) into a PIC16F628A on bread board and injected
10MHz on pin 16 (CLK IN).
I fed the NMEA data from a GPS
module (TIME and DATE) to pin 7
(RB1). On the LCD I have the UTC
TIME decoded correctly but the DATE
is always 00:00:00.
The Fix indication is fluctuating
from Fx to Fx9. On pressing S1 (View
Fix), the LCD shows:
Lat:
Lng:
00:00.0000 0
000:00.00000
On pressing S2 (View ANTH), the
LCD shows:
Ant 3.6 m abvMSL
Sats in View: 00
On pressing S3 (View SATS), the
LCD shows:
00:00dB
00:00dB
00:00dB
00:00dB
On pressing S4 (INIT GPS), the LCD
displays:
Initializing GPS
RX module now
Any comments? (V. B., Greece)
You should be able to use either
of those GPS receiver modules in the
GPS-based Frequency Reference, although it would be a little easier to
use the V.KEL VK2828U7G5LF module since it is already provided with
a 1pps output (“P”).
•
102
Silicon Chip
and tried to compile it. But I got the
following error message:
Arduino_Data_Logger.ino:18:20:
fatal error: RTClib.h: No such file
or directory
#include “RTClib.h”
I tried two different computers but
still got the same error message. Do
you know what has gone wrong? (R.
S., Epping, Vic)
• It seems like you may have an
old, incompatible version of the RTClib library on your system(s). The
With the u-blox Neo-7M module,
you’d need to perform minor surgery
to solder a wire to pin 3 of the Neo-7M
chip, in order to obtain a 1pps output.
This is a little tricky, but it can be
done if you’re careful. The location
to solder is shown in El Cheapo Modules part 10 on GPS receivers by Jim
Rowe (October 2017; siliconchip.com.
au/Series/306).
It’s not easy to tell whether the
results you were getting with your
lashup are correct. It would be better
to build the complete Frequency Reference and then see if you can decode
all of the data.
Regardless of which GPS module
you use, it should be located close to
a window so that the patch antenna
has a reasonable view of the sky. Otherwise, it won’t deliver usable NMEA
data or correctly locked 1pps pulses.
Unsure if RapidBrake
is working properly
Thank you for the quick delivery
of the parts which I ordered for the
RapidBrake project. I have one query
and one comment.
Everything went together beautifully. All the calibration settings were
easily made to almost exactly the
voltages specified. Step 6 and step 7
were done and LED1 flashed and the
relay switched on and off exactly as
it should until the jumper on JP3 was
removed. Then it did nothing at all.
I have now installed the unit in the
car with the jumper still in place and it
works perfectly. What did I do wrong?
The polycarbonate adjustment jig is
OK but the slots are cut just a bit too
wide. Despite not having even peeled
off the protective paper coverings, the
Celebrating 30 Years
only way we can reproduce this error message is to delete the RTClib
library. Installing the library provided in our download then allows the
sketch to be compiled.
Please check your “This PC\Documents\Arduino\libraries” directory and ensure there is an RTClib
subdirectory.
If so, delete it and re-install the
libraries we have supplied. You
should be able to compile the Data
Logger sketch then.
assembled jig is very sloppy, it wobbles and falls apart at the least movement. I ended up sticking it all together
with Blu-Tack.
The spacing between the two arms
on which the box rests is the same as
the distance between the mounting
holes for the nylon spacers.
Thus the heads of the screws which
hold the spacers to the box tend to sit
on top of the jig arms, making it difficult to get them to sit cleanly at the
correct angle.
You could have made the jig arms
a little closer to each other, or I could
have used countersunk screws.
Thanks for a great magazine filled
with interesting and informative articles. (T. T., Woorim, Qld)
• JP3, when inserted, allows for calibration using the Earth’s gravity as a
reference. When JP3 is removed, the
RapidBrake compensates for road
slope so it is no longer activated due
to gravity being at an angle (ie, when
on a slope).
So after JP3 is removed, you will
find that tilting the RapidBrake will
not cause the relays to switch and this
is correct.
It is only when mounted in a vehicle
which is braking, with deceleration is
in the same plane as the RapidBrake
PCB, that the relays will switch at the
required calibrated forces.
By successfully achieving calibration, you have already tested the
RapidBrake’s operation. JP3 should be
removed for normal operation. You can
only test the RapidBrake then by braking hard and watching the indicators.
Thanks for your comments regarding the jig. We will adjust the
next batch we make to solve these
issues.
SC
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Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable.
siliconchip.com.au
Celebrating 30 Years
December 2017 103
Next Month in Silicon Chip
Arduino LC Meter Shield
This kit from Altronics is based on Jim Rowe’s project in the June issue but has some changes to make it even
easier to use. It can be built into the MegaBox which we described this month, or into a separate laser-cut case.
nRF24L01+ 2.4GHz Wireless Data Transceiver Modules
Jim Rowe describes the operation of these 2Mbps digital radio modules with software that lets you communicate with a
pair of Arduino or Micromite modules. This article was held over in favour of the GY-68 and GY-BM modules in this month.
Easy-to-build Theremin has ten transistors
The eerie sound of the Theremin has featured in many movies from the distant past right up to the present. Why
not build this latest design from Silicon Chip which was first published almost 50 years ago? That means it uses
cheap and easy-to-get transistors and other bits (and no SMDs). You can take it to your next musical gig.
Touchscreen Controller for Induction Motor-based Lathes
This project uses a Micromite LCD BackPack along with our Induction Motor Speed Controller to drive a lathe. It
works with Induction Motors that have separate Start and Run windings and provides the ability to reverse the motor as well as control and monitor its speed.
Note: these features are prepared or are in preparation for publication and barring unforeseen circumstances, will be in
the next issue.
The January 2018 issue is due on sale in newsagents by Thursday, January 4th. Expect postal delivery of subscription
copies in Australia between January 2nd and January 16th.
Notes & Errata
Advertising Index
50A Charger Controller, November 2016: there is a discrepancy between the
circuit and PCB design. The circuit shows D4 connected between ground and
the junction of the 100kW and 22kW resistors, but on the PCB it is connected
to the wrong end of the 100kW resistor. We suggest constructors cut the track
and fix this with a wire link. The next batch of PCBs will have this flaw corrected.
Deluxe Touchscreen eFuse, July 2017: the text on page 47 (last paragraph,
third column) states that IC4 is connected... after D7. Instead, it is connected
after D1 and the associated 1W resistor.
Universal Battery Valve Power Supply, August 2017: the circuit on page 35 shows
the labelling on diodes D4 & D5 swapped. In other respects, the circuit is correct.
3-way Active Crossover for speakers, September & October 2017: the PCB
has pads for diode D4 but it was not shown on the PCB overlay or the circuit diagram because it isn’t strictly needed. It can be left off or fitted below D3 if desired.
Kelvin the Cricket, October 2017: The circuit on page 44 shows switch S1
connected to pin GP0/pin 7. It should connect to GP2/pin 5. The PCB is correct.
Modifications to Universal Battery Valve Power Supply, Circuit Notebook,
October 2017: there is a mistake in the circuit diagram which shorts out the
secondary of transformer T2 by joining pins 5 and 8. Diodes D5 and D6 should
connect to pin 5 of T2 only while diodes D4 and D7 and the 470µF capacitor
connect to pin 8 of T2.
6GHz+ Touchscreen Frequency Meter, October-December 2017: in the
first article on page 33 of the October 2017 issue, the parts list states that the
1PS70SB82 UHF diodes are supplied in the SOT-23 package. They are actually
in the smaller SOT-323 (SC-70) package. The board is designed to accept this.
Super-7 AM Radio, November 2017: there are two errors on the circuit of
page 49 & 49. Schottky diode D1 should be a BAT46, not BAT56. The capacitor
connected to the emitters of Q6 & Q7, the output coupling capacitor, is 470µF,
not 100µF. Also the parts list shows Q7, a BD140 as an NPN type. It is PNP, as
shown correctly on the circuit.
Finally, the text on page 47 has errors in two sentences: “It oscillates at a frequency set by the parallel resonant circuitry connected to its emitter, ie, the primary of T3 plus VC3 and VC4” and “the output signal of the mixer/oscillator appears at the bottom end of this secondary and is fed to the primary of transformer
T2”. The first sentence should refer to T2 while the second should refer to T3.
Altronics.................................. 74-77
Aussie Rechargeable Irons.......... 12
Dave Thompson......................... 103
Digi-Key Electronics....................... 3
Emona Instruments.................... IBC
Hare & Forbes.......................... OBC
High Profile Communications..... 103
Icom Pty Ltd................................. 13
Jaycar............................... IFC,49-56
Keith Rippon Kit Assembly......... 103
LEACH Co Ltd.............................. 33
LD Electronics............................ 103
LEDsales.................................... 103
Microchip Technology................... 11
Mouser Electronics......................... 7
Oatley Electronics........................ 10
Ocean Controls.............................. 8
PCBcart...................................... 41
Premier Batteries......................... 37
ROLEC OKW................................. 5
Sesame Electronics................... 103
SC Online Shop...................... 88-89
SC Radio, TV & Hobbies DVD...... 91
Silicon Chip Subscriptions.......... 83
The Loudspeaker Kit.com.............. 9
Tronixlabs................................... 103
Vintage Radio Repairs............... 103
Wagner Electronics...................... 63
104
Silicon Chip
Celebrating 30 Years
siliconchip.com.au
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