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Contents
Vol.31, No.12; December 2018
Features & Reviews
12 “The Grand Tour”: the incredible Voyager missions
Way back in 1977, two Voyager spacecraft were launched to probe Saturn,
Uranus, and Neptune. 41 years later – and way past their expected demise –
they’re now the most distant man-made objects in space – by Dr David Maddison
44 The Arduino Uno’s cousins: the Nano and Mega
Arguably the world’s most popular micro (especially amongst hobbyists), the
Arduino has two not-so-well-known variants, the smaller Nano and the larger
Mega 2560. Here’s an explanation of the differences – by Jim Rowe
74 El cheapo modules, part 21: stamp-sized audio player
SILICON
CHIP
www.siliconchip.com.au
No-one would have
believed that the two
Voyager spacecraft
would still be
operational 41 years
later. But they are,
albeit running on
limited power – Page 12
You won’t believe how sensitive
this new Magnetometer is. We
found it could detect a pin head
centimetres deep! – Page 24
Less than five dollars gets you the DFPlayer mini: a tiny (21 x 21 x 12mm) digital
audio player which can handle MP3, WMA and WAV, in mono or stereo, off either
a microSD card or USB flash drive with a capacity up to 32GB – by Jim Rowe
Constructional Projects
24 An incredibly sensitive Magnetometer to build
A magnetometer detects changes in magnetic fields, whether natural or manmade. This magnetometer is SO sensitive you have to make allowances for such
things as waves and tidal flow! – by Rev Thomas Scarborough
38 Amazing light display from our LED Christmas tree . . .
Last month we brought you our EXPANDABLE Christmas Tree, which is already
very popular with readers (judging by the number of kits sold!). Now we present a
controller to provide spectacular display options – by Tim Blythman
66 A Useless Box
What does a Useless Box do? Well, not much – it’s pretty useless! But build this
nonsense project and you’ll keep the kids (and grandkids) amused until at least
next Christmas – and probably way beyond – by Les Kerr & Ross Tester
84 Low voltage DC Motor and Pump Controller (Part 2)
With a huge array of options to suit YOUR particular application, this motor/pump
controller will handle up to 40A DC on a nominal 12V supply. We couldn’t fit it in
last month – so we’ve used the time to include even more! – by Nicholas Vinen
Your Favourite Columns
58 Serviceman’s Log
Travelling makes me go cuckoo! – by Dave Thompson
78 Circuit Notebook
(1) Simple guitar practice amp
(2) Accurately measuring voltage and current at the same time
(3) 1kHz crystal-locked sinewave oscillator
94 Vintage Radio
1948 AWA compact portable Model 450P – by Graham Parslow
Everything Else!
2 Editorial Viewpoint
99
4 Mailbag – Your Feedback 103
64 Christmas Showcase
104
siliconchip.com.au
82 SILICON CHIP Online Shop 104
Ask SILICON CHIP
Market Centre
Advertising Index
Notes and Errata
Want to be able to
individually address
each LED in our
expanding
Christmas Tree?
We show you how
to do it with this
new controller
– Page 38
They can’t resist
flicking the switch.
But when they do,
Froggy comes
out and turns
the switch back
off again! Build
it for Christmas!
– Page 66
This month’s El Cheapo
module is intriguing:
a digital audio player,
complete with its own
amplifier and card
reader, for less than
$5 out of China!
– Page 74
www.facebook.com/siliconchipmagazine
SILICON
SILIC
CHIP
www.siliconchip.com.au
Editor Emeritus
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Publisher/Editor
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Phone (02) 9939 3295
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PhD, Grad.Dip.Entr.Innov.
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Associate Professor Graham Parslow
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Brendan Akhurst
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Editorial Viewpoint
Love or hate Google, the massive
EU fine is a joke
While the €4.34 billion fine that an EU court imposed
on Google this July (which they are in the process of
appealing) may be legally sound, it is based on a lack
of technical understanding. The judgment is likely to
decrease competition in the smartphone space, the
very opposite of what the court is trying to achieve.
This case has echoes of United States v. Microsoft
Corp from back in 1998-2001 (ah, nostalgia!). The argument then was that Microsoft’s integration of Internet Explorer (IE) into
Windows had an anti-competitive effect on companies that offered other web
browsers. Microsoft lost that case (wrongly, in my opinion, despite the rage
I feel when I see IE) but ended up with a slap on the wrist.
In the more recent Google case, the argument is as follows: Google allows
smartphone makers to use their Android phone operating system for free as
long as they follow certain rules. One of them is that Google Search and the
Chrome browser must be included on the phone or else the Google Play Services (used by many Google apps) is not made available.
They also made payments to some manufacturers and networks to make
the Google search engine the default on their phones. And they threatened to
withhold some Google apps from manufacturers who sold devices running
“forked” versions of Android – ie, not the versions distributed by Google.
According to the EU court, part of the reason that this is so bad is that the
Google Play Services is a “must-have” and the threat to withhold is a serious
one. But I wonder if these people have ever travelled to China.
All Google services are blocked in mainland China. As a result, Android
phones sold in China don’t include any apps which rely on them, or the
Google search features. And yet Android phones are incredibly popular in
China, with over half a billion sold last year.
And having these Google apps on your phone hardly locks you into using them. It’s dead easy to install a different browser or select a different default search engine. You can disable the Play Store on day one and simply
download and install app packages manually from web pages, if you want.
There’s absolutely nothing stopping you.
Part of the complaint was that 95% of Android users use Google search,
which the EU court thinks indicates that they are somehow locked in. Maybe
most users prefer to use Google search because it’s the best option available
– did they consider that? When I was in China and couldn’t access Google
search, I tried several alternatives and found them very poor by comparison.
I’m of two minds about Google as a company. Many of their products are
amazing but their corporate culture appears to be quite toxic and they seem
to allow politics to invade their decision making in troubling ways. But I
still don’t see how this fine can be justified. The logic of the court simply
doesn’t hold up to scrutiny. It makes the whole thing look like a shakedown.
It is quite reasonable that they expect vendors to bundle some of their
apps on phones if they are going to have free use of their operating system.
The alternative would be to charge manufacturers to use Android, which I
expect would increase the cost of phones. That’s hardly helping consumers
and it is likely to have an impact outside of the EU too.
While I can certainly see how some of the restrictions that Google have
placed on the use of Android could be seen as mildly anti-competitive, they
also have the beneficial effect of providing standardisation across multiple
generations of smartphones, avoiding a fragmented nightmare of different,
incompatible versions of the operating system and software.
So on balance, I think Google should be rewarded for providing Apple
some competition and giving consumers more options, not punished.
Nicholas Vinen
Derby Street, Silverwater, NSW 2148.
2
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
siliconchip.com.au
Australia’s electronics magazine
December 2018 3
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”.
The government’s My Health Record
system is not what you think
Nicholas Vinen’s editorial on the
Government’s My Health Record initiative is interesting for several reasons.
I assume that Nicholas is relying on
the information provided by the Australian Digital Health Agency regarding the opt-out period during which
people can elect not to be registered
for a My Health Record.
The headline story put out by the
government is that “My Health Record is an online summary of your key
health information. When you have a
My Health Record, your health information can be viewed securely online,
from anywhere, at any time – even if
you move or travel interstate.”
This gives the impression, repeated
by Nicholas, that My Health Record
is an electronic medical record and
everyone who does not opt-out will
get one. The realities, as detailed in
the depths of the myhealthrecord.gov.
au website and in the many submissions to the Senate Inquiry, are very
different.
At the end of the opt-out process,
people will only be registered for a
My Health Record; they will not get
an online summary of their health
information – patients and GPs will
need to provide and upload this data
and then ensure it is always accurate
and current.
My Health Record is not a medical
record system; it is a hybrid, summary
system that tries to meet the needs of
both health providers and consumers
but fails to satisfy either. Claims as to
the benefits of medical record systems
do not apply to My Health Record –
they are very different beasts.
There is not enough room in this letter in which to fully cover the many
concerns that have been expressed
about the lack of justified benefits. That
includes the costs to health practitioners of maintaining two record systems
4
Silicon Chip
(their own and the government’s), the
risks of inappropriate access (both by
authorised and unauthorised users,
including by the government itself)
and the potential dangers to minority groups.
Readers who wish to inform themselves of the many different opinions
surrounding My Health Record should
consult the more than 100 submissions
to the Senate Inquiry, at siliconchip.
com.au/link/aaly
You can also review the evidence
provided at the public hearings at
siliconchip.com.au/link/aalz and
the final report of the inquiry at
siliconchip.com.au/link/aam0
The Australian Privacy Foundation
has almost 200 links to articles and
press coverage of the debate during
the opt-out period at https://privacy.
org.au/campaigns/myhr/
Bernard Robertson-Dunn, BEng,
MEng, PhD, MIEAust, MIEEE, MIET
Australian Privacy Foundation
Chair, Health Committee
Agreement with concern over
online private data collection
Regarding Nicholas Vinen’s wellwritten observations about the collection of personal information by search
engines, social media and online services in the October 2016 issue. I was
once told that if you’re not paying for a
product or service, chances are you’re
the product.
This is certainly true of all the email
& messaging, photo sharing, time management, file storage and basically any
free content sharing services available
on the internet – we can access more
high-quality free services than ever, in
return for just about any information
that the provider wants to glean from
us with that service. That information
becomes their property to be sold!
More often than not, that information is used (legally) to target online advertising specifically to you, the user,
Australia’s electronics magazine
and your specific data is of little interest to the party collecting it. Whether
that’s desirable to you is an individual
decision; the lines between legality and
morality in this area move more quickly than most of us can keep up with.
One must also consider the increasing risk of private data being stolen and
used without permission for nefarious
purposes by unknown third parties, as
the potential of that information in less
law-abiding hands is limitless.
Callum Martin,
via email.
More doubt over eHealth records
Leo has taught you well, Nicholas.
My opinion is you are a very naive
young man, sadly.
Please publish a story on the technology being employed to host eHealth
in Australia, what safeguards are actually in place and what would be the
ideal scenario needed to make this
monster safe.
How far from the essential security
technologies are we with this project?
I think we cannot trust the Minister on
this or anything else. I would like to
see some facts to back up your opinion.
Chaim Lee,
Newtown, Qld.
Giandel inverters suitable for
UPS project are now in stock
Amongst many projects that I have
built over the years from Silicon Chip
articles, when the UPS project was introduced (May-July 2018; siliconchip.
com.au/Series/323), I just had to build
it. So I sourced all the parts required
except for the specified inverter.
I ordered and paid for an inverter
from the distributors, Giandel, and received an email back confirming my
order, including a tracking number
from Australia Post. Two days later, I
received a further email informing me
that the inverter that I had ordered was
no longer in stock.
siliconchip.com.au
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siliconchip.com.au
Australia’s electronics magazine
December 2018 5
To keep a long story short, Silicon
Chip kindly published a list of alternative inverters in the July 2018 issue,
but they were generally more expensive than the originally specified one
or did not have the remote control that
was an integral feature of the UPS design. Further, I was not prepared to
pay $899 when they started appearing on eBay.
After checking the Giandel website
every week or so for the last several
months, they now have an updated
version of that inverter for sale. It is
slightly wider but otherwise seems
identical. And the good news is that
they will send it post-free for $180.
Perhaps others who may have been
in my situation will find this information useful.
Ian Hawke,
Glossodia, NSW.
Sourcing obsolete 2SA970
low-noise transistors
I am writing in regards to the letter published in the Ask Silicon Chip
section of the November 2018 issue,
titled “Amplifier troubleshooting and
sourcing low-noise transistors”.
Having recently completed the excellent 20W Class-A amplifier that
uses these transistors, I can confirm
that these transistors are still available from www.futurlec.com for the
princely sum of US$0.10 each.
I knew at the time that they were
no longer available in Australia so I
bought 20 of them for future use just
in case and would suggest that others
who are building amplifiers which
specify these transistors do the same.
My experience of Futurlec is their
delivery is quite slow but they stock
many items that are hard to get elsewhere at very reasonable prices.
Another option is eBay. Some local
sellers can supply these transistors (in
Melbourne). The prices are higher but
if time is of the essence, this may be
the best option. See: siliconchip.com.
au/link/aam1
Peter Clarke
Adelaide, SA.
Some ESP-01 modules
have assembly faults
I want to provide some feedback on
the ESP-01 WiFi module I purchased
from your online shop (Cat SC3982).
Two of them did not work correctly.
On close examination, I noticed that
on both these boards the capacitor/re6
Silicon Chip
Australia’s electronics magazine
sistor next to the crystal and closest to
the ESP8266 IC was not in the correct
location but was soldered to the end
of the crystal.
Fortunately, I can work with SMD
components (though these tiny ones
are a struggle!) and I removed and replaced it in the correct location. The
modules then worked.
I also noticed that the SPI flash supplied on these boards is the “8Mb”
PUYA Semiconductor P25Q80H that
has a dodgy reputation for reliability
(particularly the number of times they
can be flashed). Also, the flash tool reports them as 4Mb when the datasheet
says 8Mb.
I replaced the SPI flash chip on all
eleven boards I purchased with the
Winbond W25Q32JVSSIQ 32Mb SPI
flash (about $1.25 each from Digikey).
Not only should this yield an improvement in reliability but it also gives me
a lot more room if I decide to put my
own customised code on the units,
and I can run the SPI bus at 80MHz.
I have upgraded all the boards to
the v1.6.2 AT firmware and they are
all working well.
Gerard Sexton,
Park Orchards, Vic.
Response: we examined the other modules we have in stock and couldn’t see
any with the same fault. We will look
out for this fault in future. Your comments about the flash chips are interesting. It doesn’t surprise us that these
modules would use the cheapest possible flash chips, given their low price.
Using Steam Whistle project
to make surf sounds
The white noise generator and
voltage-controlled gain feature of the
TDA7052A in the Steam Whistle/Diesel Horn project in the September issue
(siliconchip.com.au/Article/11226)
could potentially be used to make a
Surf Sound Generator.
This could be done by implementing
three digital swell envelopes in the PIC
firmware, averaging them and adding
a constant minimum noise level. The
resulting value would then define the
PWM output which controls the output volume.
The phase and duration randomisation could perhaps be implemented by extracting data from the white
noise generator. The swell envelopes
could either be generated algorithmically or could be implemented using
a look-up table.
siliconchip.com.au
Since only the noise and PWM amplitude outputs are
required, front panel potentiometer controls for Volume,
Surf Speed and Noise Floor could be provided.
I had been toying with the idea of designing such a circuit
using an ATtiny25 (it’s ten times faster than the PIC12F617)
but I have not had time to do so yet. Perhaps you would
consider designing such a project.
Erik Christiansen,
via email.
John Clarke responds: thanks for that suggestion. I had
considered using the voltage-controlled amplifier to make
a surf sound generator. We just recently published the Tinnitus/Insomnia Killer, based on the same white noise generator chip. I will consider designing a surf sound simulator based on the same IC in the near future.
405-line TV system was high definition for its day
The November article on the restoration of the 1939 UK
TV set was a most enjoyable surprise. I’d love to have been
involved in the project. I would like to read more similar
stories, please.
That set’s 405-line system, used from 1936, could still
be seen in Australian TV’s early (pre-videotape) years in
the form of 16mm film telerecordings of BBC programs
sold here.
As the ABC’s representative attached to the old Film
Censorship Board (which then had to classify all imported
programs), I saw these not on a regular TV screen, but as
projected prints, and even at such enlargement the picture
quality was remarkably good (despite losses in the recording process itself – simply filming a TV screen!).
You became aware of the coarse line structure only
with a staircase effect on slightly off-horizontal objects,
and anyone in a striped suit made merry moiré patterns,
but the vision was generally better than the equivalent
American 525-1ine NTSC kinescopes.
I think the BBC used something called spot wobble, giving slight vertical oscillation to the beam and so thickening
the lines, and there may have been other improvements
since their TV began in 1936.
So by the standards of those pioneering times, the
claim for “high definition” was not exaggerated; even 20plus years later the picture was still acceptable – and was
watched by Australian TV audiences.
On a Beta (yes!) tape, I have a documentary called “TV
Is King” which, while not going much into technicalities,
gives a fascinating look at pre-war UK and German TV.
For any of your readers interested, I might be persuaded
to light the boiler under the faithful old Sony and copy it.
Brian Wallace,
Dora Creek, NSW.
Vintage TV restoration is surprisingly popular
It was fascinating to read Dr Hugo Holden’s account of
the Prewar HMV TV in the November issue (siliconchip.
com.au/Article/11314).
Whilst I’ve realised that restoring a vintage radio is within
the capabilities of an experienced technician, even without
much specific knowledge, I never expected that it would be
possible to fix up an old TV set like that, except for those
who used to do that for a living. Even then, I thought there
would have to be a limit to picture tube life.
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Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
How wrong I was! I now belong to a few vintage radio
and TV groups on Facebook. Most members are US-based
and I’m continually astounded at both the success rate for
people who clearly have no real understanding of TV (or
electronics) technology and the absurdly low prices Americans pay for “vintage” TVs.
Quite often people post how they’d just bought old
round-tube 1940s sets with working tubes, often for under $US100! Unfortunately, getting one shipped out here
is frighteningly expensive.
What is even more incredible is the number of people
who are even getting old 1950s round tube colour sets
working, often with the original picture tubes.
There are even working examples of the very early RCA
sets where the colour dots were printed onto a flat glass
sheet that was surrounded by a monochrome type glass
envelope. Who would have imagined those tubes lasting
for more than 60 years?
It does take me back. My first job was in a TV repair
shop in Brisbane in the early 1970s, and one of my tasks
was the “$60 Overhauls”.
At that time a lot of the old original ‘50s TVs were showing their age, but with colour broadcasts just a few years
away, people were understandably reluctant to invest in
new Black and White sets.
The answer was the aforesaid overhauls, where a reconditioned picture tube would be fitted, any suspect
parts were replaced, the tuner was overhauled and the
set generally returned to some semblance of its original
condition.
I didn’t know too much about old TVs at the time, except what I’d read in Serviceman columns in Electronics
Australia.
The message there was pretty clear: “Paper capacitors chuck ‘em!” So for each common model, I got out a sheet
of cardboard and made up a list of all the paper capacitors
they used, and just did a bulk “re-cap”.
This approach did not sit well with some of the older
staff, who seemed to have an almost Calvinistic distaste
for such labour-saving shortcuts, but then the “Big Boss”
saw what I was doing and pronounced it a splendid idea,
and that was that!
Now, a half-century later, that is exactly the approach
being used by amateur TV restorers, with remarkably high
success rates.
What has further astounded me is that there are quite
a few group members here in Australia, and many of the
“old bangers” I worked on nearly 50 years ago are still
going, many with the original tubes! Never in my wildest nightmares would I have expected to see an HMV M1
still functional....
The Facebook groups can be quite entertaining, particularly the endless conflicts between the old veterans like me
who are at pains to point out that TV servicing isn’t quite
as hard as many people think, and the wannabe guys, clueless “net-sperts” whose primary mission in life seems to
be to prove the exact opposite...
Keith Walters,
Riverstone, NSW.
Battery valves were not used in car radios
I really enjoy Ian Batty’s articles on Vintage radio and
the one in the October 2018 issue on the Emerson 838
siliconchip.com.au
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Hybrid portable was extremely interesting.
The Editor’s note on page 102 did rather surprise me,
however, as battery valves were not used in hybrid car radios for a variety of reasons, such as filament fragility with
vibration and wide variation of filament voltage which
would have reduced the reliability of the sets.
Car radios were manufactured as hybrids with valves
and transistors as you stated. The valves used in all the
hybrid car radios I serviced used indirectly heated valves
with heaters usually requiring 12V.
These valves were designed to operate nominally from
12V and as I remember from viewing some of the data sheets,
they were rated up to around 33V on the plate.
My Vintage Radio article in the December 2006 issue was
on a typical hybrid radio, an AWA 976A. Other manufacturers such Astor also made hybrids.
Rodney Champness,
Mooroopna, Vic.
Using strain gauges to demonstrate bridge loading
I read with interest the item in the Mailbag section of
the October 2017 issue (pages 10 & 11) relating to strain
gauge beams. It reminded me of some problems I had to
solve back in the 80s, as a technical officer at a tertiary
teaching organisation.
An experimental set-up had been designed for the students, so that they could observe the effect of a load travelling across a bridge. A weighted vehicle would roll along
the top of a U-channel, with two strain gauges mounted in
the middle of the bridge, one on the top side of the bottom
of the channel and the other on the underside.
Australia’s electronics magazine
December 2018 9
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10
Silicon Chip
The beam was about 2m to 3m in
length and was only supported at each
end, to allow for some bending and
change in length.
The two strain gauges were wired
to an amplifier and the output went
to an X-Y plotter. The academic in
charge kept calling for more amplification and added weight to the vehicle,
as the output to the plotter was low;
but both the conditioning amplifier
and recorder were at maximum sensitivity. I was brought in to try to fix
this problem.
The beam was visibly deflecting
with the vehicle at mid-span. The principal output was two peaks that coincided with the vehicle’s axles passing
the strain gauges. Torsional stability of
the beam was poor.
Fortunately, the vehicle was designed not to become derailed, although it wobbled most alarmingly.
I was surprised that the gauges remained adhered to the steel!
Then, one night, the answer woke
me up – with that blinding flash of inspiration. The initial designer/installer of the gauges had failed to consider
where the neutral axis of the section
actually was.
The gauges were wired as if one was
in tension and the other in compression. The one on the underside was in
(considerable) tension but the one on
top was NOT in compression; it was
in much the same value of tension. So
the output from one gauge virtually
negated the other.
What was being observed was the
cross section flexing as the trolley
moved over the gauges. The transverse sections of the gauge foil were
detecting the transverse localised
bending and stretching of the section
and the effect was being observed as
two peaks.
My solution was to add two more
gauges to form a full bridge. Then I just
had to reduce the weight of the vehicle and lower the amplification of both
the conditioning amplifier and plotter
considerably. The beam no longer visibly deflected nor suffered from the
terrible torsional problem.
Unfortunately, the academic now
complained that the localised wheel
loading effect could not be observed!
Oh well, you cannot please them all
of the time.
The next problem I had to solve was
how to drive the plotter properly. The
plotter had one axis wired to show the
Australia’s electronics magazine
deflection signal and the other was set
to move via an internal time-base, so
the trolley had to travel quickly and at
a constant speed to generate an accurate plot – not easily achieved.
It would be better for the second
plotter axis to be fed the measured
position of the vehicle along the
bridge.
Our solution was to take a single
piece of nichrome resistance wire and
tightly stretch it parallel to, but insulated from, the rolled steel section.
A pick-up finger was attached to the
vehicle which could slide along the
wire. So, the voltage drop could be
detected and fed to the displacement
axis of the plotter.
A significant current was fed
through the nichrome wire (in the tens
of amps), producing a voltage gradient
across it, and the voltage signal from
the vehicle pick-up was amplified and
fed to the plotter.
Now it was possible to move the vehicle at a slow speed or even allow it
to remain stationary, so that the students could observe exactly what was
happening in the experiment.
Ray Smith,
Hoppers Crossing.
TDR Dongle modifications
to cure ringing
I build Jim Row’s TDR Dongle
for Oscilloscopes (December 2014;
siliconchip.com.au/Article/8121) but
I had to make a minor modification to
achieve good performance.
Upon powering the unit up initially, the output waveform rose to a plateau, but shortly thereafter exhibited
significant ringing at around 10MHz
on the positive voltage step, shown
in the scope grab below.
Testing with different power supplies, cables and scopes indicated that
these were not to blame.
Careful examination of the circuit
suggested that parasitic capacitance
at the input to IC3 (the output amp,
an OPA356) might be to blame, espesiliconchip.com.au
cially considering the very high bandwidth of this IC.
I connected a 4.7kW resistor from
the inverting input of this IC (pin 2) to
ground, which eliminated the ringing.
The second scope grab below shows
the cleaned-up waveform – about as
close to perfect as you can get.
With this modification in place,
I conducted tests on a 15m coaxial
cable with various terminations and
the results precisely matched expectations.
The easiest way to make this modification is to solder one end of the resistor to the junction of the 2kW resistor and 82pF cap, and the other end
to the ground pin of the nearby SMA
connector.
I would like to express my appreciation to Jim Rowe for designing such a
useful and compact unit.
It will be an invaluable aid for demonstrating cable reflections and impedance terminations to University engineering students – something which
is usually shrouded in mystery unless
seen in operation.
John Leis,
Toowoomba, Qld.
Jim Rowe responds: this seems to be a
good solution for anyone who experiences the same ringing problem.
I didn’t experience that problem
with my prototype. That may be due
to component values and IC performance varying slightly from sample
to sample.
Graphic analyser wanted as companion
for graphic equaliser
I have been using my Playmaster
Graphic Equaliser (Electronics Australia, May 1979) in conjunction with
its companion Playmaster Graphic
Analyser (EA, February 1980) since
soon after those projects were published.
The graphic equaliser has developed
a couple of dead bands and while it
was out on the troubleshooting bench,
I thought that maybe it was time to upsiliconchip.com.au
grade to your June/July 2017 design
(siliconchip.com.au/Series/313).
The graphic analyser has great utility. It makes equalising the listening
environment a breeze, so perhaps it
is time for you to consider publishing a companion unit for the 2017
equaliser.
The 1980 analyser was a multiplemode unit which was intended to become a permanent part of a hifi setup,
doubling as a horizontal VU display
or as a power meter.
But I have only ever used it as an
analyser and it spends most of its life
in the cupboard. As I play most of my
material through my computer into my
hifi system, I don’t use the analyser’s
built-in pink noise generator.
Instead, I use an audio editor program on the computer to create a pink
noise wave file which I play through
the system for analysis.
May I suggest the following as a
potential construction project? A battery operated, hand-held analyser
with built-in microphone and multiple LED bargraph display, but no pink
noise generator and no other novel
uses designed in. It could be a useful
instrument.
The Tinnitus/Insomnia Killer project from the November 2018 could
be used as a pink noise source
(siliconchip.com.au/Article/11308),
or alternatively, a computer or smartphone.
Hopefully, there would be some
reader interest in such a device.
Robert Allan,
Hunters Hill, NSW.
John Clarke responds: Thanks for the
suggestion for a graphic analyser. With
a suitable calibrated microphone,
room acoustics and loudspeaker response could be adjusted using an
equaliser to give a flat response. We
will investigate the pros and cons of
such a design.
Technology has changed since the
1980 analyser, meaning that it could
be done in software. It may be difficult
to justify a hardware-based analyser
design due to the cost.
There are numerous spectral analyser software packages available
such as www.techmind.org/audio/
specanaly.html
You can use this to apply pink noise
to your audio system and observe the
response on the computer screen. A
calibrated microphone would be required.
SC
Australia’s electronics magazine
December 2018 11
THE INCREDIBLE
MISSIONS OF
In 1977, two Voyager spacecraft
were launched from Earth:
Voyager 2 on August 21 and
Voyager 1 a few days later, on
September 5.
Their mission? To probe the gas
giant planets (Jupiter, Saturn,
Uranus and Neptune) and beyond.
Amazingly, and beyond all
expectations, their mission
continues 41 years later (albeit
with much of the on-board
equipment shut down to conserve
dwindling power).
Voyager 2 is now humanity’s most
distant object and travelling away
from Earth at a speed of
62,000km/h (17km/second!).
Radio signals to or from Voyager,
at the speed of light, take 20
hours – one way!
The
“Grand Tour”
by Dr David Maddison
12
Silicon Chip
Australia’s electronics magazine
This background
image, the crescent
view of Jupiter, was
taken by NASA Voyager
1 on March 24, 1979 –
almost four decades ago!
Regrettably, there will be no
more pictures from Voyager –
to save power its cameras were
turned off in February 1990 –
already way past its planned life!
siliconchip.com.au
B
oth Voyager spacecraft are still operational and
sending back valuable data, using what would be
regarded today as vintage electronics.
Voyager 2 is also now humanity’s third most distant object, surpassed only by Pioneer 10, by a relatively small
margin. But communications with Pioneer 10 were lost in
January 2003.
Voyager 1 is now in interstellar space, ie, mostly beyond
the influence of the Sun, including both its solar wind and
magnetic field. It is in the space between star systems and
as of going to press, Voyager 2 is now thought to be entering interstellar space as well.
The Voyager spacecraft were launched as a result of a
once-in-a-lifetime opportunity.
In 1964, Gary Flandro of the Jet Propulsion Laboratory
(JPL) in California made the observation that a particular
alignment of outer planets Jupiter, Saturn, Neptune and
Uranus (the gas giants) would enable a single spacecraft
to visit all of them on a single mission, using the gravitational slingshot effect to go from planet to planet without
needing extra fuel.
This trajectory became known as the “Grand Tour”.
This special planetary alignment only occurs once every
175 years and was to occur in the later 1970s. The alternative was to send individual spacecraft to each of these four
planets, at much greater expense.
NASA decided to send two spacecraft on the Grand Tour,
with some slight differences between the two trajectories
(see Fig.1). This would significantly reduce the time taken to visit the planets of interest and also allow additional
post-launch options, such as the possibility for Voyager 1 to
visit Pluto instead of Saturn’s moon Titan. It also reduced
the risk of a launch failure derailing the whole mission.
Voyager 2 was launched on 20th August 1977, before
Voyager 1, which was launched on 5th September 1977.
This is because they were numbered based on their ex-
Fig.1: trajectories of the Voyager spacecraft, showing
their close encounters with the gas giants which gave
opportunities for taking photos and scientific observations
as well as using the gravitational slingshot effect to make
their way to the outer planets and beyond the solar system.
Voyager 1 visited Jupiter and Saturn and made a close
flyby of Saturn’s moon Titan (considered more important
than passing Pluto) while Voyager 2 visited Jupiter, Saturn,
Uranus and Neptune.
pected arrival at Jupiter.
Even though Voyager 1 was launched 16 days after Voyager 2, due to different trajectories, Voyager 1 arrived at Jupiter four months before Voyager 2.
The different trajectories provided the option for Voyager 2 to make close passes of Uranus and Neptune if desired, depending on scientific findings which were to be
made along the way .
Fig.2: the trajectory of Voyager 2 for its Jupiter encounter, showing the many navigational considerations that had to be
taken into account to maximise the information to be obtained.
siliconchip.com.au
Australia’s electronics magazine
December 2018 13
Fig.3: a depiction of Voyager showing some of the primary spacecraft systems and instruments.
A much longer mission than intended
The Voyager mission has been so successful that it has
been extended a couple of times. The original primary mission of the Voyager program was to visit Jupiter and Saturn.
Along the way, the probes made many important discoveries such as detecting volcanism on Jupiter’s moon Io and
finding unexpected intricacies in Saturn’s rings.
The mission was then extended to allow Voyager 2 to
visit Uranus and Neptune, which it did in 1989. Uranus and
Neptune had not been visited before or since. After that, a
further mission extension was granted to both spacecraft;
known as the Voyager Interstellar Mission (VIM), its purpose is to explore the outer limits of the Sun’s influence
and further beyond.
The VIM is planned to extend to 2020 and possibly longer,
subject to the availability of electrical power on the probes.
The journey to interstellar space
The graphic opposite shows the location of the Voyager spacecraft relative to our solar system. The heliosphere is the ‘bubble’
surrounding the Sun, extending well past the orbit of Pluto. It has
its origins in the solar wind, the stream of charged particles constantly emitted from the Sun.
It is not a sphere; it is distorted into a teardrop shape due to
the interaction of the heliosphere with the interstellar wind, the
atomic particles moving past from interstellar space. Within the
heliosphere, there is the termination shock, which is the sudden
slowing of the solar wind from a speed of 300-700 kilometres
per second to a much slower speed as it encounters the interstellar wind.
The heliosheath is the outer layer of the heliosphere, where the
solar wind slows further, becoming denser and hotter as it interacts and ‘piles up’ against the interstellar wind. The heliopause is
the point at which the pressure of the solar and interstellar winds
are in balance and the solar wind turns around and flows down
the teardrop tail of the heliosphere.
The bow shock is formed much like the bow wave of a boat,
as the solar system moves through the atomic particles of the interstellar medium.
Voyager 1 is heading above the plane of the planets while Voyager 2 is heading below the plane. Voyager 1 is in the interstellar
medium and has been since August 2012.
14
Silicon Chip
As of 5th October 2018, Voyager 2 is believed to be about to exit
the heliopause due to an observed increase in cosmic ray activity. The exact time of transition cannot be predicted as the shape
of the heliopause varies due to solar activity and its location with
respect to the asymmetric heliosphere.
Pluto has an average distance from the Sun of 39.5 astronomical units (AU), where 1AU is the average Earth-Sun distance.
Voyager 1 is currently at a distance of 144AU from the Earth and
Voyager 2, 119AU.
For more details, see: https://bgr.com/2018/10/08/voyager-2heliopause-interstellar-space/
Also see: www.jpl.nasa.gov/news/news.php?feature=7252
Australia’s electronics magazine
siliconchip.com.au
Fig.4: the Multi-Hundred Watt Radioisotope Thermoelectric Generator (MHW-RTG) as used on both Voyager
spacecraft. At the start of the mission each unit provided
157W of electrical power (2400W thermal) and each
spacecraft had three generators providing 471W at launch,
diminishing all the time due to radioactive decay.
The objective of the VIM is to obtain useful information on
interplanetary and interstellar fields, particles, and waves.
Between 2020 and 2025, the probes’ remaining instruments
will need to be shut down to preserve electrical power.
After 2025 (some reports say 2030), the decay of the nuclear fuel onboard the spacecraft will reduce their power
supplies to the point that neither will be able to function
and they will finally “go dark”.
Spacecraft design
When they were designed in the early-to-mid 1970s, no
spacecraft had yet been made to operate at such distances
from the Earth.
Both spacecraft are identical and after ejection of their
propulsion module weighed 825kg, 117kg of which is the
scientific instruments (see Fig.3). All spacecraft systems
were designed with high reliability and redundancy in
mind. The craft are stabilised on three axes to ensure the
antennas remained pointed toward Earth; the Sun and
Canopus are used as guide stars.
Three separate onboard computer systems are used for
different tasks, each having a backup system. Their magnetic tape data storage capacity is 536 megabits (a whopping 67 megabytes); enough to store 100 full resolution
(800 x 800 pixel) 8-bit (256 grey scale) photos.
For power, each spacecraft has three plutonium-based
radioisotope thermoelectric generators which initially provided a continuous 470W of electric power, although the
power output is continuously diminishing due to radioactive decay.
A 3.66m high-gain antenna dominates the structure of
siliconchip.com.au
Fig.5: the plutonium fuel spheres within the MHWRTG assembly, along with layers of protection to avoid
contamination in the event of a launch accident.
each spacecraft and they also have a coaxial low-gain antenna for radio science observations. The bulk of the onboard electronics is contained within ten boxes which
form a ten-sided structural “bus”. They also carry hydrazine fuel for 16 thrusters.
Of the 16 thrusters, 4 are for trajectory correction and 12
are for attitude control. There are three pairs of primary attitude control thrusters and three more pairs of secondary
thrusters for redundancy, giving a total of 12.
All thrusters are the Aerojet model MR-103, which are
still in production today. They deliver 0.89N or 0.09kgf (kilogram-force) of thrust. The attitude control thrusters on the
Voyagers have been fired hundreds of thousands of times
during the mission but typically only “puffs” are emitted
for milliseconds at a time, to make the tiniest corrections.
As a testament to the reliability of the thrusters, it was
noticed in 2014 that the thrusters on Voyager 1 had been
degrading in their performance and using more fuel than
they should. It was decided to switch to the trajectory correction thrusters, which had not been turned on in 37 years
(since the spacecraft’s encounter with Saturn) and they
worked perfectly. This measure saved fuel, extending the
mission life of the craft by 2-3 years.
External to the bus are booms for the radioisotope generators, to keep their slight radiation as far from the sensitive
instruments and spacecraft electronics as possible. There
is also a scientific instrument boom, 2.3m long, containing most of the instruments (with a steerable platform at
the end for the optical instruments) and a 13m long magnetometer boom.
The instruments are mounted on a boom as they are
Australia’s electronics magazine
December 2018 15
Fig.7: the Flight Data System (FDS) computer used in the
Voyager spacecraft.
Fig.6: this is what a radio telescope image of the radio
signal from Voyager 1 looks like. The Very Long Baseline
Array (VLBA) was used to capture this image on February
21st, 2013. The elongated shape is a consequence of the
antenna configuration. The width of the radio signal
shown is 1 milliarcsecond, or at the distance of 18.5 billion
kilometres when the image was produced, about 80km.
radiation-sensitive and also sensitive to magnetic fields
from the spacecraft. The nearest boom-mounted instrument to the generators is 4.8m away, with the spacecraft
in between, and the closest platform-mounted instrument
is 6.4m from the generators.
The steerable platform on Voyager 2 once got stuck as it
swung around Saturn but the problem was fixed by sending a sequence of commands to turn the platform one way
and then the other multiple times, to free it.
The thrusters are mounted on the outside of the bus,
along with a combined planetary radio astronomy and
plasma wave antenna system, comprising of two 10m-long
elements mounted at right angles to each other. (Plasma
is the fourth state of matter and is a gas in which atoms
which have had some or all electrons stripped from them
coexist with those electrons.)
There are also two star trackers, a calibration instrument
and a golden record containing sites and sounds of Earth
and other information about the origin of the spacecraft, in
Interesting Voyager Facts
Five trillion bits of data have been jointly transmitted by both
Voyager spacecraft. That’s enough data to fill seven thousand
music CDs or over 4.5 terabytes.
The power of the radio signal currently received from the Voyager spacecraft on Earth is between about 10-14W and 10-19W.
A modern basic digital watch consumes about 10-6W (1 microwatt) so the signal power received is between 100 million times
and 10 trillion times lower.
Here are some informative documentaries about the Voyager
probes on YouTube:
https://youtu.be/xZIB8vauWSI
https://youtu.be/seXbrauRTY4
16
Silicon Chip
case an alien civilisation finds it (see opposite).
The high gain antenna is coloured white but the rest of
the spacecraft is black and blanketed for thermal control
and micrometeorite protection, while some areas are coated in gold foil and according to one claim, some areas are
even wrapped in domestic kitchen-grade aluminium foil.
Appropriate operating temperatures for the electronics are maintained by a combination of electrical heaters,
thermal blankets, radioisotope heaters (which generate
about 1W of heat through radioactive decay) and thermostatically-controlled louvres in four of the ten electronics
compartments.
Power system
Due to the extreme distances from the Sun and the long
duration of the mission, currently expected to be 48 years
total, there is no possibility of using solar panels or batteries for spacecraft power. The only viable power source
is a type of nuclear reactor called a Radioisotope Thermoelectric Generator (RTG).
At the start of the mission, the Voyager probes needed
400W of electrical power and the device to produce this
is called the Multi-Hundred Watt RTG or MHW-RTG (see
Fig.4).
This power source has no moving parts and works by
converting radioactive decay heat to electricity by many
thermocouples arranged in thermopiles. Each thermocouple generates a small direct current from the temperature
difference across the junction of two dissimilar metals. The
heat comes from the radioactive decay of spheres containing plutonium-238 (Fig.5).
When the outputs of these thermocouples are combined,
a substantial amount of electrical power is produced.
Would the Voyagers be much
different if built today?
If the Voyager spacecraft were built today, they would be similar in many respects; the basic layout, type of instruments, thermal control and power source would likely be very similar. But
the computers would probably be very different, given the chips
with much larger computing power and memory available today.
The cameras would also be much more sensitive to light and
have higher resolutions as they would use solid-state imaging
sensors rather than tubes.
Australia’s electronics magazine
siliconchip.com.au
Fig.8: the Voyager Digital Tape Recorder. It was designed
with extreme longevity in mind.
Safety was always a consideration, so to avoid the possibility of radioactive contamination in the event of a
launch accident, the fuel is surrounded by many strong
protective layers.
Telemetry system
Signals from Earth are sent on the S-band (2-4GHz) and
signals are sent back to the Earth on the X-band (8-12GHz)
at up to 21.3W. There is also a 28.3W S-band backup for
the downlink.
During the Jupiter encounter, data was sent back to Earth
at 115,200bps and from Saturn at 44,800bps. The difference is due to the extra distance to Saturn as received
power decreases due to the inverse square law, hence the
Fig.9: the 11 science instruments (which include the radio
antenna), a photo calibration target and the radioisotope
thermoelectric generator, mounted far away from the
scientific instruments to avoid interference.
lower data rate.
Today, data is received at just 160bps due to the extreme
distance.
Data is received by the NASA Deep Space Network (DSN)
which comprises receivers in Goldstone, California; Madrid, Spain; and Canberra (see Fig.6).
Voyagers’ Golden Record
In case an alien civilisation ever encounters these spacecraft,
there is a gold-plated copper record that contains 115 images (plus
a calibration image) and a variety of sounds of Earth along with a
plaque with instructions for playing the record and indicating the
origin of the spacecraft.
The record is also coated with ultra-pure uranium-238, which
decays into other elements over time, enabling the age of the
spacecraft to be determined. As a courtesy to aliens, a stylus is
even supplied with the record!
siliconchip.com.au
The audio stored on the record is about 54 minutes long and
the images have a resolution of 512 lines.
A video showing the images (with the video author’s own
soundtrack) can be seen at: https://youtu.be/50HN6HAmeis
Parts of the audio track can be found on YouTube, but not a complete playlist. There is a video of the story of making the record at:
https://youtu.be/Mx0eNqINNvw
A copy of the record can be purchased from various sources
including https://ozmarecords.com/
Australia’s electronics magazine
December 2018 17
These receivers have occasionally been supplemented by
others such as Parkes Radio Telescope, NSW and the Very
Large Array, New Mexico. Also, the antennas of the DSN
have been upgraded over time, plus new software has been
sent to the Voyagers to implement some data compression.
Onboard computer systems
The Voyager computer systems are based partly on the
computer system used on the Viking Orbiter spacecraft
which went to Mars in 1976, a decision based on budgetary
restrictions and a desire for standardisation. For Voyager,
this computer was called the Computer Command System
PGH-Rate [Ions (>70MeV/Nucleon) per second
LA-1 Rate [Ions (>0.5MeV/Nucleon) per second
Fig.10: the Voyager Cosmic Ray System. It consists of three
different types of instruments: four low-energy telescopes
(LETs), facing in a variety of directions; two double-ended
high-energy telescopes (HETs) at far left and far right; and
the electron telescope (TET), directly beneath LET A.
Fig.11: data from 2012 showing Voyager 1 crossing through
the heliosheath into the interstellar medium. Voyager 2
is seeing similar radiation patterns now as it enters the
interstellar medium. You can see live updates for the
radiation measurement instruments for both spacecraft at
https://voyager.gsfc.nasa.gov/data.html Source: Wikipedia
user Stauriko.
(CCS) with additional computers added being the Flight
Data System (FDS) and the Attitude Articulation Control
System (AACS).
None of the computers on Voyager use dedicated microprocessors; they are instead built from discrete logic ICs.
The Voyager computers have a total of 69.656kB memory if
both memory banks in each computer are counted.
The CCS is the “master” computer and is responsible for
memory management and commands sent to the FDS and
the AACS. It uses almost identical hardware to the Viking
computer but runs heavily revised software. Due to its capability of in-flight reprogramming, the code has been im-
Preparing the spacecraft for the Voyager Interstellar Mission (VIM)
Both spacecraft have exceeded their expected mission durations
by a long margin. Many preparations have been made to upload
new software and shut down various instruments and services
to reduce the electrical load, to compensate for the diminishing
power output of the nuclear power sources. Their power output
is diminishing by about 4W/year.
The most important mission requirement is to maintain each
spacecraft’s High Gain Antenna pointed to Earth. This requires
that the thrusters which make tiny changes to spacecraft attitude
continue working.
A second requirement is that software instructions must be
sent to enable the spacecraft to continue to operate autonomously,
with programmed sequences of events to perform and to return
data, even if the spacecraft lose their ability to receive command
signals from Earth.
The table at right shows the electrical loads on Voyager 1 that
have so far been turned off to save power since the VIM started.
Further planned shutdowns include termination of Digital Tape
Recorder operations (already shut down on Voyager 2) and shutdown of the gyros for normal operations, to be powered up only
when needed. After 2020, the remaining operational instruments
will be turned off permanently or periodically turned on and off to
share the remaining electrical power.
There is enough fuel for attitude control to last until 2025. Beyond 2025, there is just one remaining task for the Voyagers and
18
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that is to carry information to possible intelligent spacefaring alien species, who may find the spacecraft and discover that they
are not alone.
Voyager 1 Load
Power Turned
Saved
Off
IRIS Flash-off Heater
31.8W 1990
WA Camera
16.8W 1990
NA Camera
18W
1990
PPS Supplemental Heater
2.8W
1995
NA Optics Heater
2.6W
1995
IRIS Standby A
7.2W
1995
WA Vidicon Heater
5.5W
1998
NA Vidicon Heater
5.5W
1998
IRIS Science Instrument
6.6W
1998
WA Electronics Replacement Heater
10.5W 2002
Azimuth Actuator Supplemental Heater
3.5W
2003
Azimuth Coil Heater
4.4W
2003
Scan Platform Slewing Power
2.4W
2003
NA Electronics Replacement Heater
10.5W 2005
Pyro Instrumentation Power
2.4W
2007
PLS Science Instrument
4.2W
2007
IRIS Replacement Heater
7.8W
2011
Scan Platform Supplemental Heater
6.0W
2015
UVS Replacement Heater
2.4W
2015
UVS Science Instrument
2.4W
2016
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Fig.12: LECP data for Voyager 1, showing an increase in
galactic cosmic rays as the spacecraft enters interstellar
space. The data points are obtained from many different
angles by rotating the detector platform. Source: NASA/
JPL-Caltech/JHUAPL.
proved continuously over time.
The CCS can execute 25,000 instructions per second
and has two independent memory banks of 4096 18-bit
words of non-volatile plated-wire memory (a variation of
core memory).
As mentioned earlier, there is a duplicate of each computer system on each spacecraft, in case one fails. The CCS
is also compartmentalised so that if one part of one CCS
fails, it can use the good part in the other CCS.
The duplicate CCS computers can operate in three modes:
individual, where each CCS performs independent tasks;
parallel, where each CCS works on a task together; or tandem, where the same task is performed by each CCS and
the results are cross-verified. The latter was used during
close encounters with the planets where an error could be
disastrous.
The FDS is the system which collects, formats and stores
all engineering, scientific and telemetry data. If the amount
of data collected exceeds the capacity to transmit it back to
Earth, excess data is stored on magnetic tape until downlink capacity is available.
The FDS contains two banks of 8192-word 16-bit CMOS
RAM and can execute 80,000 instructions per second (see
Fig.7).
The FDS was the first spacecraft computer to use volatile
CMOS RAM which requires constant power to maintain the
memory. Even a momentary loss of power would mean a
complete loss of memory. To ensure constant power to the
FDS, each unit has a dedicated power line from the radioisotope generators.
It was decided that no further redundancy was required
because if power was lost from those for whatever reason,
the mission had no hope to continue in any case.
The reason for having separate CCS and FDS systems is
the high data rate from sensors such as cameras. The CCS
may have been overwhelmed by the amount of data but the
FDS was explicitly designed to handle it. However, these
were the last spacecraft where the two functions were handled by separate computers. Like the CCS, the FDS can be
reprogrammed in flight.
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Fig.13: the key elements of the Low Energy Charged Particle
instrument.
The AACS is a modified CCS and is used to control the
scan platform stepper motors, thruster actuators, handle attitude control and implement thruster logic. It has a crucial
task which is to keep the spacecraft antennas pointed toward Earth. The AACS has two banks of 4096, 18-bit words
plated wire memory.
All the software was originally written in Fortran 5. Later software was written in Fortran 77 and later again in C.
One problem in later years of the mission was to find programmers who were familiar with these languages.
For more information, see: http://forums.parallax.com/
discussion/132140/voyager-1-2
The data storage system
For times when data was being acquired faster than it can
be transmitted back to Earth, such as during planetary encounters where many photos were being taken, excess data
was recorded on a digital tape recorder (DTR) – see Fig.8.
In addition to image data, every week, each spacecraft
records 48 seconds of high-rate plasma wave system (PWS)
data at 115.2kbps. This data is recorded on the tape and
transmitted back to Earth once every six months.
The long delay between transmissions is due to competing resources in the NASA Deep Space Network (DSN)
required to receive the data and the fact that the primary
mission of the spacecraft has been completed. The operation of the DTR on Voyager 2 was ended in 2007 due to a
failure of the PWS, which occurred in 2002.
The operation of the DTR has either been terminated (or
soon will be) on Voyager 1 this year due to the inability to
receive its data at 1.4kbps, which is the minimum speed it
can transmit on its telemetry channel.
At a distance from Earth of 19 light hours, the maximum
data rate which can be received is much lower than this.
As mentioned above, the currently possible rate is around
160bps on the 34m radio telescopes within the DSN; it is
somewhat higher on a 70m radio telescope.
The tape recorders were designed to be extremely robust
and reliable. The tape heads were designed to last for several thousand kilometres of tape travel.
Australia’s electronics magazine
December 2018 19
Fig.14 (left): the actual Low Energy Charged Particle
instrument in Voyager.
Fig.15 (above): a 70s-era photograph of the Fluxgate
magnetometer system used in Voyager spacecraft.
Scientific instruments
The Voyager spacecraft have ten dedicated scientific instruments and also used the spacecraft’s communications
system for certain investigations, for a total of eleven (see
Fig.9). A description of each system follows. Four instruments are still operational on Voyager 1 and five on Voyager 2.
1. Cosmic Ray System (CRS) (operational)
The CRS is still running on both spacecraft and measures
both cosmic rays and other energetic particles from outside
the galaxy, the Sun and particles associated with the magnetospheres of planets. It has a wide range of energy resolutions and one of its functions is to study the solar wind.
It comprises three different types of instrument,
to measure different energy levels and also to determine the direction of the particles detected (Fig.10).
All instruments in the CRS are based around solidstate detectors.
The CRS was instrumental in determining the location
of the heliosphere’s termination shock, the heliosheath,
the heliopause and Voyager’s entry into interstellar space
(see Fig.11).
2. Low-energy charged-particle (LECP) experiment
(operational)
This instrument is still running on both spacecraft.
It detects sub-atomic and atomic particles such as
electrons, protons and alpha particles along with elements around planets, in interplanetary space and
now interstellar space. These particles may originate from the Sun, galactic cosmic rays or planets.
It consists of two subsystems, the Low Energy Magneto-spheric Particle Analyzer (LEMPA) and the Low Energy
Particle Telescope (LEPT) – see Figs.12, 13 & 14.
This instrument helped establish the shape of the mag20
Silicon Chip
netospheres of Saturn and Uranus and establish the point
of transit of the spacecraft into interstellar space, along
with the CRS.
3. Magnetometer (MAG) (operational)
The magnetometer instrument is still running on both
spacecraft. Each spacecraft carries two low-field magnetometers that measure from 0.002nT to 50,000nT and
two high-field magnetometers that measure from 12nT to
2,000,000nT (2000µT/2mT). By way of comparison, the
Earth’s magnetic field is between 25,000nT (25µT) and
65,000nT (65µT) at the surface.
The magnetometers are located at various positions
along a 13m-long boom to minimise interference from
spacecraft electronics. The purpose of the magnetometers is to measure the magnetic field of the Sun, planets,
moons and currently, interstellar space.
Among the many discoveries made by the MAG were
the magnetic fields of Uranus and Neptune, which are
not aligned with the planets’ rotational axes, and are of
a similar strength to Earth’s. It has also detected strong
magnetic fields outside the solar system.
4. Plasma Science (PLS) experiment (operational on
Voyager 2 only)
This system is still running on Voyager 2 but has failed
on Voyager 1. The purpose of this experiment is to determine how the solar wind varies with distance from the
Sun, study the magnetospheres of the planets, study the
moons of the planets and detect interstellar charged particles (see Figs.16 & 17).
5. Plasma Wave Subsystem (PWS) (operational)
The PWS uses two 10m-long dipole antennas mounted at right angles to detect the electric field from plasma
near planets and the interplanetary and now interstellar medium, in the frequency range of 10Hz to 56kHz.
The same antenna system is also used by the PLS. A recording of plasma waves as Voyager 2 encountered Neptune may be heard at https://youtu.be/dJ8Dz5ZmqGM
6. Imaging Science System (ISS) (switched off)
The Voyager spacecraft each have a wide-angle and
narrow-angle video camera mounted on a moveable scan
platform. Each camera is equipped with several different
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Voyager’s future encounters
Fig.16: the Solar wind pressure on Voyager 2 throughout
the mission, as measured by the PLS. Note the dramatic
decrease in 2007. This happened after the spacecraft passed
the termination shock and entered the heliosheath. It did this
much earlier than Voyager 1 due to the asymmetric shape of
the heliosphere, caused by the interstellar magnetic field.
filters that can be selected as necessary, which are selective
for specific wavelengths of light, including wavelengths
associated with chemical elements and compounds.
The wide-angle camera has filters on a colour
wheel selective for Blue, Clear, Violet, Sodium
(589nm), Green, Methane (541nm and 619nm) and
Orange. The narrow-angle camera has filters for
Clear, Violet, Blue, Orange, Green and Ultraviolet.
The wide-angle camera has a 200mm focal length
with a 60mm objective and aperture of f/4.17 while
the narrow-angle camera has a 1500mm focal length
with a 176mm objective and aperture of f/11.8.
The cameras use a monochrome vidicon TV tube
(model B41-003; see Fig.18) made by General Electro-dynamics Co, which is a storage tube that can
store a high-resolution video image for 100 seconds.
The image area in the tube is 11.14mm x 11.14mm,
consisting of 800 lines with 800 pixels per line.
After a picture is taken, 48 seconds is required to electronically read the image, after which the image is cleared
by flooding the tube with light to prepare for the next picture. The greyscale images are sampled with eight bits
per pixel, so they required 5,120,000 bits of storage space
(640kB) on magnetic tape for transmission back to Earth.
As mentioned earlier, images of Jupiter could be
transmitted back to Earth at 115,200bps while images
of Saturn were sent at 44,800bps, so each image of Jupiter took 44 seconds to transmit, and 114 seconds for
Saturn. Colour images were generated by merging images taken with various filters on the colour wheel.
Some of the many discoveries made with the ISS are the
great turbulence in the Jovian atmosphere, the intricate
patterns in Saturn’s rings, vulcanism on Jupiter’s moon
Io and an indication of an ocean beneath the ice of Jupiter’s moon Europa.
The cameras on both spacecraft were turned off decades
ago due to a lack of sufficient light for useful imaging, the
lack of objects to image and to save power. Voyager 1 took
its last photo (mosaic) in 1990, the famous “Solar System
Family Portrait” while Voyager 2 took its last photos when
it encountered Neptune in 1989.
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In about 40,000 years, Voyager 1 will come within 1.7 light
years of the star Gliese 445 and in 56,000 years it will pass
through the Oort Cloud, a collection of icy objects and a possible
source of solar system comets. This will be followed by close
encounters with the stars GJ686 and GJ678 in 570,000 years.
An interesting calculation concerning the encounter with
Gliese 445 is shown at: http://mathscinotes.com/2013/06/
voyager-1-and-gliese-445/
Voyager 2’s next closest encounter, apart from interstellar
dust and gas clouds will occur in about 40,000 years when it
will come within 1.7 light years of the star Ross 248. At that
time, Ross 248 will be the closest star to the Sun and just 3.02
light years from Earth. Then in 60,000 years, it will pass the
Oort cloud. In about 296,000 years it will come within around
4 light years of the star Sirius.
It is difficult to predict with certainty where either spacecraft will go next.
Fig.17: the plasma detector, which comprises two Faraday
Cups.
7. Infrared interferometer spectrometer and radiometer
(IRIS) (non-operational)
Infrared light is outside the visible range, at the red
end of the spectrum. It is absorbed by various molecules
and the extent of absorption at various wavelengths
can be used to determine their chemical composition.
The IRIS has three functions. It can determine the presence of various compounds in planetary and moon atmospheres, determine the temperature of the various bodies
and can measure the total amount of light reflected from
the bodies.
8. Photopolarimeter Subsystem (PPS) (failed)
When non-polarised light from the Sun is reflected or refracted by various materials, such as ice
crystals in a planet’s atmosphere, it acquires a polarisation. Polarising filters block light with certain types or orientations of polarisation, selectively allowing light with a specific polarisation through.
Voyager’s PPS was designed to image planetary atmospheres, rings and their moons’ surfaces using
a 150mm focal length telescope and various colour and polarising filters (a total of 40 combinations
Why didn’t Voyager explore the
Kuiper Belt?
There are three mains reasons why the Voyager probes did
not gather data on the Kuiper Belt, a region between about 30AU
and 50AU from the Sun which contains many small bodies, remnants from the formation of the solar system.
1) The Kuiper belt was unknown when the spacecraft were
launched; it wasn’t discovered until 1992, Voyager 1 had already
passed it when it was discovered and Voyager 2 was well into it.
2) The Voyager imaging system would not have been sensitive enough to make out the small objects in the Kuiper Belt.
3) The only telescope that could have found objects for Voyager to investigate was not working correctly at the time (Hubble).
NASA’s New Horizons mission is currently investigating these
objects. Further details are at:
https://blogs.nasa.gov/pluto/2018/02/28/the-pisperspective-why-didnt-voyager-explore-the-kuiper-belt/
Australia’s electronics magazine
December 2018 21
Fig.18: a Vidicon tube, as used in the Voyager cameras, along
with sample images. Courtesy www.digicamhistory.com
were possible). It was used to distinguish between
rock, dust, frost, ice and meteor material and obtain
information about textures, compositions and distribution of particles such as in clouds and rings.
Unfortunately, the instrument on Voyager 1 failed before the Jupiter encounter and none of the data was ever
archived, so it was turned off.
The PPS on Voyager 2 also suffered multiple failures
and was of limited use but it was used to watch stars
dip behind the rings of Saturn, Uranus and Neptune, to
examine their structure and behaviour.
9, Planetary Radio Astronomy (PRA) (non-operational)
The PRA experiment is a radio receiver that covers
two frequency bands, from 20.4kHz to 1345kHz and from
1.2MHz to 40.5MHz. It was designed to detect radio emissions from the planets, including those from lightning
and plasma resonance. It uses and shares with the PWS
the two 10m-long antennas mounted at right angles to
each other, in a “V” shape.
10. Radio Science System (RSS) (non-operational)
The RSS used the Voyager communications system to pass radio signals through planetary and moon
atmospheres and ring systems, which were then
picked up by receivers in the Deep Space Network
to determine atmospheric and ring properties. This
technique is generally known as radio occultation.
The system can also be used to precisely determine
the spacecraft trajectory so the shape, density and mass
of nearby bodies could be determined.
11. Ultraviolet spectrometer (UVS) (non-operational)
UV light is just outside the visible spectrum at the
blue end and is responsible for causing sunburn.
The UVS was used to measure the distribution of major
constituents in the atmospheres of planets and moons,
the absorption of UV light by bodies with atmosphere
as the sun is occulted, the UV “airglow” emissions of
various bodies and the distribution of hydrogen and
SC
helium in space.
Mission status, data and communications activity
You can view the real-time mission status of the Voyage probes
at: https://voyager.jpl.nasa.gov/mission/status/
Data from all instruments are freely available on a variety of websites, so if you have a theory you want to test, you are welcome
to do so. A good place to start is https://voyager.jpl.nasa.gov/
mission/science/data-access/ but be aware that many data links
are outdated or not working. However, if you look hard enough,
you will find current data.
If you want to check if the Deep Space Network is transmitting
or receiving data with Voyager, you can go to https://eyes.nasa.
gov/dsn/dsn.html and look for codes VGR1 (Voyager 1) or VGR2
(Voyager 2). See recent image below.
Fig.19: the Deep Space Network status on 8th October 2018, showing the Canberra DSN station receiving data from
Voyager 2 at 8.44GHz with a power level of -108.42dBm (1.44 x 10-14W). The typical data rate is currently 160bps.
Data is transmitted from Earth at around 19kW. On 9th October 2018, the Goldstone DSN station in California
received data from Voyager 1 with an astonishingly low received power of -152.44dBm or 5.70 x 10-19W!
22
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Australia’s electronics magazine
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Australia’s electronics magazine
December 2018 23
Extremely Sensitive
Magnetometer
It might not look much like your traditional metal detector.
It’s not! But for ferrous metals, its sensitivity is on
a par with – or better than – some of
the best commercial designs.
We’ve found this magnetometerbased design can find ferrous
metallic objects smaller
than the head of a pin!
by Rev.
Thomas Scarborough
Features
Features
• Highly sensitive – will detect magnetic
field strength changes of around
three nanoTeslas!
• Fast start-up (about ten seconds)
• Complete immunity to stationary
magnetic fields
• Differential (two-channel) design for
a high degree of immunity to magnetic
“noise”
• 12V battery powered . . . or 12V DC plugpack
• Uses common components
• Easy initial set-up (takes about ten
minutes)
• Easy to use (mostly controlled by a
single knob)
24
Silicon
iliconCChip
hip
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electronics magazine
magazine
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Measuring its sensitivity
It’s difficult to measure the sensitivity of a device like this without specialised equipment. But using some
clever techniques, it is possible.
For example, it is possible to generate a weak magnetic field of any
desired strength by placing a magnet
with a known field strength some dis-
Magnet thickness (inches)
T
his design is a major revision
of an earlier detector which was
published in Europe more than
a decade ago. (Elektor, May 2007)
That was described as an “incredibly sensitive” design . . . but this one
is significantly more sensitive!
Three significant improvements
have been made compared to that
older design:
• A second channel has been added,
to cancel out spurious signals
• It has triple the number of amplification stages
• It adds a relay switch, where the earlier design only had a LED readout
The advantage of two channels is
that magnetic pulses picked up by
two channels will cancel each other
out, while those detected by only one
channel – or predominantly one channel – will trigger the relay.
Also, temperature and power supply
variations will have much less effect.
This dramatically increases stability
and sensitivity, especially in the presence of magnetic “noise”.
The advantage of a relay switch is
that the magnetometer may be put to
good use by switching things. This device is not merely for making your fortune . . . for example, it could sound
a remote alarm when a vehicle approaches.
Having said all that, this magnetometer uses common components and is
easy to set up and use.
But it is a serious machine. When
carefully adjusted, it will detect changes in magnetic fields down to about
3nT (nanotesla) or 30 microgauss. That
puts it on a par with some of the best
commercial designs. It will, for example, detect metallic objects which are
smaller than the head of a pin.
1/16
1/8
¼
3/8
½
5/8
¾
1
1¼
1½
2
3
4
1/32
0.3
0.6
0.9
1.2
1.4
1.6
1.8
2.2
2.5
2.9
3.4
4.5
5.3
1/16
0.4
0.7
1.1
1.4
1.8
2.0
2.3
2.8
3.2
3.6
4.4
5.7
6.9
1/8
0.5
0.8
1.4
1.8
2.2
2.6
2.9
3.5
4.1
4.6
5.6
7.3
8.8
¼
0.7
1.0
1.7
2.2
2.7
3.2
3/6
4.4
5.1
5.8
7.0
9.2
11
3/8
0.7
1.1
1.9
2.5
3.1
3.6
4.1
5.0
5.8
6.6
8.0
10
13
½
0.7
1.2
2.0
2.7
3.4
3.9
4.5
5.4
6.3
7.2
8.8
12
14
5/8
0.7
1.3
2.2
2.9
3.6
4.2
4.8
5.8
6.8
7.7
9.4
12
15
¾
0.7
1.4
2.3
3.0
3.8
4.4
5.0
6.2
7.2
8.2
9.9
13
16
1
0.8
1.4
2.4
3.3
4.1
4.8
5.5
6.7
7.8
8.9
11
14
17
1¼
0.8
1.4
2.5
3.5
4.3
5.1
5.8
7.1
8.4
9.5
12
15
19
1½
0.8
1.5
2.6
3.6
4.5
5.3
6.1
7.5
8.8
10
12
16
20
Magnet diameter (inches)
2
0.8
1.5
2.8
3.8
4.8
5.7
6.6
8.1
9.6
11
13
18
22
3
0.8
1.6
3.0
4.2
5.3
6.3
7.2
9.0
11
12
15
20
25
Table 1: this
chart from the
USA (so it’s in
inches!) shows
the distance from
the magnet where
you’d expect to
find a 5 gauss
field strength.
(Courtesy K&J
Magnetics,
Pennsylvania,
USA).
tance away from the device. The field for measuring or quantifying magnetic
strength of common types of magnets fields. In fact, it totally excludes all stacan be determined based on the ma- tionary magnetic fields. It is designed
terial and size.
for maximum sensitivity.
Table 1 shows a chart of standard neNote that environmental conditions
Distance (in inches)
a single
neodymium magnet
in free
odymium magnets
fromfrom
K&J
Magnethave
a major influence on the magspace where the field strength drops to 5 gauss.
ics, Inc of Pennsylvania.
This shows netometer, so that it may work very
the?distance
from variously sized
nemuch better, or very much worse than
Diameter
? Thickness
?
odymium magnets at which the field a typical metal detector.
strength can be expected to be around
It also has applications:
five gauss, or 500 microTeslas.
• As a metal detector: Any nearby ferThe inverse cube law (intensity = 1
rous objects will distort the magnet÷ distance3) can then be used to figic field in their vicinity. Move the
ure out the field strength at greater disMagnetometer through that field and
tances from the magnet.
it will pick up the variation and alert
For example, according to the chart,
you to their proximity.
a neodymium magnet of 3/8-inch di- • As a magnet sensor: It reacts to small
ameter and 1/8-inch thickness regisneodymium magnets at two to three
ters 5 gauss (500µT) at a distance of
metres’ distance, and large magnets
1.1 inches (28mm). Our Magnetometer
much further. It reacts to many magcan detect a similar magnet moving at
netised objects as well; for instance,
a distance of 2.7 metres.
it will pick up a moving magnetised
This is 96 times (2700mm ÷ 28mm)
pin about 20-30cm away.
the specified distance for 5 gauss. So • As a vehicle detector: It will pick up
we can calculate the field strength as
a standard car alternator at several
500µT÷963 = 555pT.
metres’ distance and it will pick up
However, we also have to compensome trucks a block away (eg, in my
sate for the fact that the actual dimenhome city, municipal trucks).
sions of the magnet are 9mm diameter • As a pet flap sensor: Attach a neoand 2.5mm thickness (apparently, this
dymium magnet to the animal’s colis a metric magnet). That gives about
lar and the Magnetometer could be
70% of the volume of the specified
used to open the flap automatically
magnet.
as the animal approaches. Foreign
So we can determine that the apanimals will not be able to enter or
proximate sensitivity of this Magexit through the flap.
netometer is around 380pT (555 x • As a tsunami alarm: If mounted
70%). And that is in a magnetically
close to the water’s edge, it will
‘noisy’ environment.
pick up the magnetic field of the
ocean (see below). The ocean will
What it’s useful for
recede just before a tsunami, so if
This Magnetometer works best as a
you connect the output to a timer
magnetic field detector. It is less suited
which will trigger an alarm in the
The prototype Magnetometer, mounted inside a concrete pipe. While keeping
the circuitry very rigid, we are not recommending you copy our method!
siliconchip.com.au
Australia’s electronics magazine
December 2018 25
L1
MIXER
AMPLIFIER
L2
AUTO
BIAS
MULTI-STAGE
AMPLIFIERS
BLANKING
TIMER
OUTPUT
SC
20 1 8
Fig.1: block diagram of the Highly Sensitive Magnetometer. The voltages
developed across coils L1 and L2 are amplified greatly and then fed into
a differential amplifier which triggers a timer if the difference in voltages
exceeds a certain threshold. The blanking is provided to prevent the magnetic
field from the relay from re-triggering itself endlessly.
•
•
•
•
•
case of the magnetic field not being
detected for several seconds, it will
give you some warning before the
huge wave hits.
As an anti-thief alarm: It will easily detect someone picking up magnetised keys (or a phone or camera)
through a tabletop.
As a security alarm: If a magnet is
suitably mounted on a door, window
or gate, the magnetometer will detect the magnet moving when these
are opened or closed. Since the magnet needs no careful mounting, this
is very easy to set up.
As a game: Mount a neodymium
magnet inside a ball and it will detect whether the ball approaches a
target, say, or falls in a hole. Since it
reacts to the rate of change of magnetic fields, it could react to the velocity of a ball.
As a vibration sensor: If a magnet
is suspended just above one of the
magnetometer’s coils by a string
from the ceiling, or on the end of a
long ruler, the magnetometer will
detect heavy vehicles at great distances. For example, a freight train
at a few kilometres’ distance.
As a strobe light: If one omits the
power section of the circuit (see
below) and places one coil near a
speaker, blue LED3 acts as a strobe
light. Since the magnetometer filters
out frequencies above about 20Hz,
the pulses follow the beat.
Use as a metal detector
To be used as a metal detector, the
Dual Channel Magnetometer needs
some slight modifications. In theory,
one would simply move coils L1 and
L2 over earth or sand and while the
magnetometer is moving in relation
to magnetised objects, it would detect them.
But the Magnetometer is far too sensitive for searching soil or sand. The
Earth is littered with things which are
just slightly magnetised, but sufficiently magnetised to confound all search
efforts at any setting—and perhaps surprisingly, the beach is dominated by
moving magnetic fields in the ocean.
The solution to both problems is
to reduce the sensitivity as required.
When we first tested the magnetometer on the beach, it was utterly overwhelmed by moving magnetic fields of
unknown origin. By inserting 470k
resistors between the primary and sec-
The Magnetometer
had no problem
detecting these
three iron nails
inside a length
of driftwood
even from quite a
distance away AND
hidden in a whole
lot of flotsam.
26
Silicon Chip
Australia’s electronics magazine
ondary windings of each sense transformer the magnetometer was brought
back within range. This will not be the
ideal value for all transformers but will
give you an idea.
With this simple modification, it
was possible to identify the ocean as
the problem: the sensitivity needed to
be turned up or down, depending on
how far the unit was from the shore.
We then desired to find out how
strong the ocean’s magnetic fields
were. Again using the standard neodymium magnet for comparison, we
measured 47.9nT two metres from the
water’s edge and 40.6nT at 12 metres.
This clearly swamps smaller magnetic fields under the sand. For example, at 12 metres from the water’s edge,
a magnetised hairpin could be found
at only 38mm distance, not 800mm as
would otherwise be possible. Search
sensitivity is therefore reduced by
95%. Things would be better, however, on a very wide beach, far from the
water’s edge.
So what is the origin of these
oceanic fields?
In 2003, “New Scientist” reported
that induced magnetic fields had been
found in the ocean, from space. Then,
on 11 April 2018, the European Space
Administration revealed that changing magnetic fields in the ocean measured 2.0-2.5nT at satellite altitude and
provided a video of their activity on a
planetary scale (see Fig.2).
This article may represent the first
publication of provisional results on
the ground and suggests that various
further experiments may be worthwhile.
Basic design
Fig.1 shows the block diagram for
the Magnetometer, which reveals its
basic design. The detector coils, which
produce virtually no current when at
rest, are wired to two self-adjusting
amplifiers. The output of each amplifier is fed through a pair of six gain
stages. The amplified signals are then
fed to a mixer amplifier.
Finally, a timer IC with a blanking
circuit (which momentarily blanks out
instability) switches a reed relay when
the output of the mixer amplifier exceeds a certain threshold.
To save time and effort, for coils L1
and L2 we are actually using the primary and secondary windings of openframe mains transformers (ie, EI-core
siliconchip.com.au
Fig.2: satellite-based measurements showing the magnitude and polarity of the
magnetic fields generated by the Earth’s oceans on one particular occasion.
These fields are small but this Magnetometer can easily pick them up when
you are near the ocean; you need to reduce the device’s sensitivity when
looking for metal objects on the beach because of this!
or the less common C-core type). We
wouldn’t want to use toroidal transformers since these are designed to
have a minimal external magnetic
field.
Note that by using transformers as
search coils, the search area is small.
These coils may react to iron and steel,
zinc, nickel, and various alloys and
minerals, depending on whether these
are magnetised or not. They will not
react to other metals such as gold, silver, and copper.
The transformers are mounted
around one metre apart, with the circuit board, battery and controls in between. As this assembly is quite large,
it can be fitted with a carry strap or
handle. A small hand-held controller is connected via a length of cable,
with a sensitivity adjustment knob and
one blue LED which varies in brightness to indicate the detected magnetic
field strength.
The idea is that you can carry the
main unit in one hand (perhaps aided with a strap over the shoulder) and
this small external control unit in the
other hand, which you can hold in a
visible location, to observe the brightness of the blue LED.
Circuit description
The circuit is shown in Fig.3. A
changing magnetic field near the windsiliconchip.com.au
ings within T1 or T2 will produce a
voltage across those coils.
These coils are the primary and secondary winding pairs of unshielded
10A mains transformers (230VAC to
12VAC/10A). The primary and secondary windings are connected in
series and in phase to increase the
sensitivity.
You may wonder how a transformer
can sense external magnetic fields since,
in theory, its magnetic field is limited to
being within or around its core.
In fact, C-core and EI-core transformers have significant leakage flux, which
means they radiate moderate magnetic fields when powered but they will
also pick up external magnetic fields.
As we mentioned earlier, toroidal
transformers have much less leakage
flux due to their construction so would
be a poor choice in this role.
Conversely, a high-value crossover inductor might be an even better
choice than a conventional transformer as they do not have a contained magnetic field at all. A crossover inductor
with an iron core might make for the
most sensitive choice.
Regardless, the voltage from T2’s
windings is applied directly between
the inputs of IC3, an LM380N audio
amplifier chip, while the voltage from
T1’s windings first passes through
switches S2 and S3 before being apAustralia’s electronics magazine
plied to the inputs of IC1, another
LM380N.
S2 allows T1 to be disconnected
while S3 allows its connections to be
reversed. As a result, the unit can be
used in three modes. The first is single-ended mode, with T1 out of circuit.
This allows for detection of the Earth’s
magnetic field, where T2 is turned on
its own axis.
In the second mode, T1 and T2 are
both connected to IC1/IC3 and with the
same phase, which provides magnetic
noise cancellation. In the third mode,
T1 and T2 are connected to IC1/IC3 out
of phase, which gives maximum sensitivity but less stability and no magnetic noise cancellation.
The LM380N audio amplifiers have
a fixed gain of 50 times and the output
automatically settles to half the supply
voltage without the need for separate
bias resistors at the inputs.
The output of the LM380N ICs,
from pin 8, is then AC-coupled to a
series of further amplification stages via 1uF electrolytic capacitors.
These amplifiers have been carefully
designed so that they are stable, despite the high total gain provided by
all the amplifiers connected in series.
For a start, 1N4148 diodes are used to
isolate the supply rails of each amplifier IC, so that ripple from one does not
feed into another. Also, each pair of IC
supply pins is fitted with multiple bypass capacitors, including some very
high-value electrolytics. These components are vital. Output currents are
kept very low, also to reduce ripple.
Using inverters as amplifiers
IC2a-f and IC4a-f are the stages
within two unbuffered hex inverters
(4069UB). Each stage just consists of
two Mosfets, one P-channel and one
N-channel, arranged in a totem pole
arrangement, as shown in Fig.4. The
gate and source terminals are connected together while the drains connect
to the supply rails.
The result is that if the input voltage
A is high, the upper P-channel Mosfet
is switched off and the lower N-channel Mosfet is switched on, pulling the
output (Y) down. And if input voltage
A is low, the P-channel Mosfet is on
and the N-channel Mosfet is off, pulling the output up.
The term “unbuffered” refers to the
fact that this is a single stage; a conventional inverter would consist of
three such circuits in series, to give a
December 2018 27
D1 1N4148
K
CON1
S2a
REVERSE
100 F
470nF
S3a
T1
12V/10A
+12V SWITCHED
A
4700 F
470k
PRIMARY
7
LINK
2
470k
IC1: LM380N-8
IC1
3
10k
10k
100k
6
5
IC2b
3
330k
4
IC2a
100k
1
2
NP
5
4
SECONDARY
1 F
6
VR1a 1M
IC2c
470nF
470nF
IC2: 4069UB
S3b
S2b
CONNECT
D2 1N4148
47k
K
THRESHOLD
220k
10k
IC2d
100k
9
8
1000 F
470nF
VR2
10k
10 F
14
11
NP
K
10
330k
A
7
470nF
47k
13
12
A
CENTRE
DETECT
IC2: 4069UB
VR3
100k
4700 F
100 F
470nF
ZD1 3.9V
100k
IC2e
+12V SWITCHED
A
IC2f
1 F
LED1
47k
K
D3 1N4148
K
CON2
100 F
470nF
+12V SWITCHED
A
4700 F
T2
12V/10A
470k
PRIMARY
7
LINK
2
470k
3
IC3: LM380N-8
IC3
6
5
10k
100k
IC4b
3
330k
100k
4
IC4a
1
2
NP
5
4
SECONDARY
10k
1 F
6
VR1b 1M
IC4c
470nF
470nF
IC4: 4069UB
CON4 DIN SOCKET
5
2
4
3
D4 1N4148
47k
K
1
470nF
220k
CON6 DIN PLUG
5
4
3
A
THRESHOLD
9
8
10 F
1
LED3
2
K
100k
10k
IC4d
IC4e
11
NP
VR4
10k
VR5
100k
10T
10
100 F
470nF
ZD2 3.9V
K
47k
13
12
A
IC4: 4069UB
4700 F
330k
A
7
CENTRE
470nF
14
1000 F
100k
+12V SWITCHED
A
DETECT
LED2
47k
IC4f
1 F
K
HANDHELD CONTROL BOX
SC
2018
DUAL CHANNEL MAGNETOMETER
much higher gain, which is beneficial
when the gate is being used in a digital
circuit. But the unbuffered type is far
more suitable for use in a linear manner, as it is used here.
With an input voltage somewhere
between the supply rails, the two Mosfets will both be in partial conduction
and passing roughly the same current,
so the output voltage will also be be28
Silicon Chip
tween the supply rails. Therefore, by
applying negative feedback from the
output to the input via a resistive divider, we can use these unbuffered inverters as crude amplifiers with relatively high gain.
The transfer characteristic of each
stage is shown in Fig.4 (from the device data sheet). As you can see, the
response is non-linear but the gain is
Australia’s electronics magazine
quite high when the input voltage is
very close to half supply. Using the inverter in closed loop mode will mean
that in the quiescent condition, the
open loop gain is at maximum and the
response will be slightly more linear.
The first inverter-based gain stage,
built around IC2c/IC4c, has adjustable gain via dual gang potentiometer
VR1, which changes the feedback resiliconchip.com.au
S1 POWER
K
K
K
PERIOD
470nF
1000 F
CON3
+12V
0V
A
ZD3
A A
VR6
100k
470nF
D9
1N5404
10k
470nF
D6
1N4148
D5
1N4148
1000 F
K
A
A
F1 1A
8.2V
1W
POWER
LED5
K
1k
D
Q1
2N7000
100k
100k
D7
1N4148
K
S
A
G
1M
7
6
7
2
IC5
3
1 F
CA3140E
1
1M
10k
1 F
4
6
100k
8
3
IC6
7555
RLY1
5
2
5
10k
4
10k
1
10 F
1M
1000 F
K
A
1,14
2
7,8
CON5
D8
1N4148
A
RELAY
LED4
100 F
1M
6
K
2N7000
LEDS
K
A
1N4148
D G S
1N5404
ZD1–ZD3
A
A
A
K
K
K
Fig.3: the complete circuit diagram of the Magnetometer, omitting only the battery which powers it
(connected via CON3). Threshold adjustment potentiometer VR4 and magnetic field indicator LED3,
both shown at lower left, are mounted offboard, in a small handheld unit. The two similar sensor/
amplifier channels are shown above these, while the differential amplifier and timer are to the right.
CON6 is on the handheld control box, connecting to its mating socket on the unit. Also note the wiring
of T1 and T2 – their starts are indicated by the black dot.
sistance. The other part of the divider
is actually formed by the impedance
of the 1µF coupling capacitor along
with the output impedance of amplifier IC1/IC3.
Therefore, this first stage has very
high gain with VR1 fully clockwise, with the gain somewhat frequency-dependent due to the reactance of the coupling capacitor.
siliconchip.com.au
The next three stages have lower, fixed
gains of 4.7 times, 3.3 times and 2.2
times respectively. They also incorporate low-pass RC filters with a -3dB
point of around 3.3Hz each, giving an
overall -3dB point of about 1.6Hz.
The signals are then AC-coupled
by 10uF electrolytic capacitors and
subject to adjustable DC bias, set using trimpots VR2-VR5. The following
Australia’s electronics magazine
gain stages, IC2e and IC4e, are operated in open-loop mode. The adjustable DC bias allows the gain and quiescent output voltage of these stages
to be tweaked.
The resulting signal then passes through another low-pass RC filter (47k/1µF), again with a -3dB
point of around 3.3Hz. The output
voltage of IC2e/IC4e is also fed to a
December 2018 29
pending on the potentiometer settings and frequency, and
partly because we don’t know the exact gain of the stages
operating in open loop mode.
But if we assume that the open loop gain of the inverters is around 20 times and that the gain of IC2a/IC4a is set
to around 10 times, the overall gain applied to the signals
from T1/T2 is in the order of 25 million times (50 x 10 x
4.7 x 3.3 x 2.2 x 10 x 7 x 21).
No wonder this instrument is capable of such sensitivity!
Note that there are several different compatible chips
for IC2 and IC4 but you should stick to the specified HCF4069UBE type since these provide the most gain.
Fig.4: internal structure and transfer characteristics of
each of the six the unbuffered hex inverters inside a single
HEF4096UB IC. They consist of a pair of Mosfets which
can be used either as a digital inverter or as a high-gain
inverting amplifier, although the transfer characteristic is
non-linear. Reproduced from the NXP data sheet.
100kresistor, with a 3.9V zener diode and red LED in
series. This LED will therefore light if the output voltage
in that half of the circuit is above around 6V (ie, above
half supply).
The signal then passes through another gain stage (number seven, if you’re counting), built around IC2f/IC4f, with
a fixed gain of seven times, before being fed to the inverting and non-inverting inputs of op amp IC5 via another
pair of RC low-pass filters, with the same 3.3Hz -3dB point.
The overall filtering thus far has the effect of severely attenuating or even cutting out signals above
about 1Hz. This virtually eliminates false triggering from 50Hz or 60Hz magnetic fields induced by
mains currents, which are pervasive in urban areas.
IC5 is configured as a differential amplifier with a gain of
21 times.
This means that if the two input signals swing in the
same direction simultaneously, the output of IC5 will not
change. But if they swing in opposite directions, or if one
stays constant and the other changes, a signal will appear
at its output, with the difference in voltages amplified by
the gain factor of 21 times.
It’s hard to calculate the exact amount of gain applied
to the signals from T1 and T2, partly because it varies de-
Triggering the timer
When a sufficiently large magnetic signal is detected, resulting in a swing of several volts at the output of differential amplifier IC5, that pulse then triggers timer IC6. Its job
is to stretch that (possibly very short) pulse into something
longer that you will notice, as it lights up LED3, and also
to drive the coil of RLY1, to trigger any external circuitry
which may be connected via CON5.
CMOS timer IC6 is triggered when its pin 2 trigger input is pulled below 1/3 VCC, which in this case, equates
to a threshold of around 3.7V. Note that this means that the
timer will only be triggered if the output of IC5 swings low.
But if the output of IC5 swings high due to a magnetic
field of the opposite polarity, it will almost certainly swing
positive and negative a few times before settling down, so
timer IC6 will be triggered regardless of the initial polarity of the pulse.
Before pin 2 goes low, the 1000µF capacitor connected
between pins 6/7 and ground is charged up close to +12V,
via trimpot VR6 and its 1kseries resistor. Once the IC is
triggered, pin 6 (discharge) immediately goes low, discharging that capacitor.
At the same time, the pin 3 output goes high, energising
the coil of RLY1 and closing its contacts.
Since VR6 changes the time that it takes for the 1000µF
capacitor to recharge once the discharge pin is no longer
being actively driven, it controls the on-time for both RLY1
and LED4. The minimum time will be around one second
while the maximum time is around 90 seconds.
The two resistors and capacitor connected to its reset pin
Slightly undersize photo of the PCB shown at right (actual board is 224mm wide). Use this in conjunction with the
component overlay (Fig.5) when assembling the PCB.
30
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
(pin 4) prevent the output from switching on when power
is first applied, allowing the Magnetometer time to settle
before IC6 becomes active, avoiding false triggering of RLY1.
Once the timer is triggered, since output pin 3 goes high,
the gate of Mosfet Q1 is charged up close to VCC. This
causes Q1’s drain-source channel to conduct, pulling up
the trigger input (pin 3), regardless of the state of the output pin of op amp IC5.
The 100k series resistor from that output pin prevents the op amp from “fighting” this condition.
This means that IC6 cannot be re-triggered for some time.
The 10µF capacitor and 1M resistor from the gate of Q1
to ground sets this blanking time to around ten seconds.
This is important since the magnetic field around RLY1’s
coil will be picked up by the Magnetometer as soon as it is
triggered and without the blanking, RLY1 would continuously be switching on and off as the unit re-triggers itself
via magnetic feedback.
Variations
For use as a metal detector, you may wish to omit or remove all components following IC5 in the circuit. LED3
will still light to indicate changing magnetic fields.
LED3 may also be directly replaced with a 1mA meter,
bearing in mind that the magnet inside the meter should
not come close to a sensor coil.
If the relay is not omitted, the blanking circuit will be
disruptive when searching.
Construction
We have designed a PCB for this project, which is coded
good reasons
to use Switchmode –
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to industry and defence
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Fig.5: the Magnetometer PCB overlay diagram, showing
where to mount each component on the board. All controls
and most LEDs are along one edge so that they can protrude
through holes in the enclosure, including DIN socket CON4,
which connects to the handheld controls via a shielded cable.
siliconchip.com.au
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INDUSTRY AND DEFENCE
Switchmode Power Supplies Pty Ltd
ACCREDITED FOR
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COMPETENCE
Unit 1/37 Leighton Place, Hornsby NSW 2077 Australia
Tel 61 2 9476 0300
Email: service<at>switchmode.com.au Website: www.switchmode.com.au
Australia’s electronics magazine
December 2018 31
Parts list –
Extremely Sensitive Magnetometer
1
1
1
2
5
1
1
1
1
2
1
1
4
4
4
3
double-sided PCB, code 04101011; 70 x 224mm
12V coil SPST DIL reed relay (RLY1) [Altronics S4101A, Jaycar SY-4032]
SPDT right-angle PCB-mount toggle switch (S1) [Altronics S1325]
DPDT right-angle PCB-mount toggle switches (S2,S3) [Altronics S1360]
2-way PCB-mount terminal blocks, 5.08mm pin spacing (CON1-CON3)
right-angle PCB-mount 5-pin DIN socket (CON4) [Altronics P1188]
5-pin DIN line plug to suit CON4 [Altronics P1151]
horizontal 2-way pluggable terminal block (CON5) [Jaycar HM-3102]
2-way pluggable screw terminal for CON5 [Jaycar HM-3122]
M205 PCB-mount fuse clips (F1)
1A M205 fast blow fuse (F1)
100mm length of 0.7mm diameter tinned copper wire
M3 x 6.3mm tapped Nylon spacers
M3 x 25mm machine screws
M3 hex nuts
knobs to suit VR1, VR4 & VR5
Semiconductors
2 LM380N-8 2.5W audio power amplifiers (IC1,IC3)
2 HCF4069UBE unbuffered hex inverters (IC2,IC4)
1 CA3140E BiMOS op amp (IC5)
1 TLC555CN CMOS timer (IC6)
1 2N7000 small signal N-channel Mosfet (Q1)
4 ultra-bright 3mm red LEDs (LED1,LED2,LED4,LED5)
1 ultra-bright 5mm blue LED (LED3)
2 3.9V 1W zener diodes (ZD1,ZD2)
1 8.2V 1W zener diode (ZD3)
8 1N4148 signal diodes (D1-D8)
1 1N5404 3A diode (D9)
Capacitors
4 4700µF 16V radial electrolytic
5 1000µF 16V radial electrolytic
5 100µF 16V radial electrolytic
1 10µF 16V radial electrolytic
2 10µF 16V non-polarised/bipolar (NP/BP) radial electrolytic
4 1µF 16V radial electrolytic
2 1µF 16V non-polarised/bipolar (NP/BP) radial electrolytic
15 470nF multi-layer ceramic or MKT
(code 470n or 474)
04101011 and measures 70 x 224mm.
Use the PCB overlay diagram, Fig.5,
and matching photo as a guide during assembly. Start by fitting the resistors where shown on the overlay
diagram. Even though we show their
colour codes in a table, it’s a good idea
to double-check their resistance with
a DMM before installing them, since
the coloured bands can often be hard
to read accurately.
Follow with the diodes. There are
two types, eight signal diodes (D1-D8),
one larger power diode (D9) and three
zener diodes (ZD1-ZD3) of two different types, so don’t get them mixed up.
Each one must be orientated with the
cathode stripe as shown in Fig.5.
The six ICs should be installed next.
You can either solder them directly
to the board or solder sockets to the
board, then plug the ICs in later. Sockets make it easier to replace a damaged
IC but they also are prone to long-term
failure due to oxidisation, so we prefer
to avoid them.
The ICs are also polarised, so ensure that each pin 1 dot is positioned
as shown on the overlay diagram.
Be especially careful with IC2 and IC4
since they are extremely sensitive to
static discharges.
That is why there are 10kresistors
at pins 5 and 6 of IC2c/IC4c and at pin
11 of IC2e/IC4e. These points connect
to potentiometers which you touch
during operation, and any static discharge which jumps to those pots
could destroy the ICs without the series resistors for protection.
Now is also a good time to solder
Resistors (all 0.25W, 1%)
4 1MW
4 470kW
4 330k 2 220k
11 100k
6 47k
10 10kW
1 1k
1 1MW 16mm dual gang linear potentiometer (VR1)
1 10kW multi-turn vertical trimpot (3296W style) (VR2)
2 100kW multi-turn vertical trimpots (3296W style)(VR3,VR6)
1 10kW multi-turn wirewound potentiometer (VR4)
1 100kW 16mm linear potentiometer (VR5)
Miscellaneous
1 timber enclosure (9mm MDF box, 70x70mm inner dimensions)
1 2m length of four-core shielded microphone cable
1 2m length of single-core shielded microphone cable
1 1m length medium-duty figure-8 wire
2 unshielded transformers with 12V, 10A secondaries (T1,T2) (RS 504-127)
1 small enclosure for LED3 and VR4
1 12V battery (small SLA or eight D cells with battery holder)
various lengths and colours of hookup wire
heatshrink tubing
Epoxy glue
32
Silicon Chip
Australia’s electronics magazine
We used 8x Alkaline cells for power
but bear in mind that with a 100150mA drain they won’t last long!
Ten rechargeable NiMH or NiCd
cells might be a better bet . . . or
even a 12V SLA or LiPo battery.
With 20:20 hindsight, though, we’d
think seriously about a 4 x 18650
rechargeable Li-ion cell pack (14.8V).
siliconchip.com.au
NOTE: SHIELD BRAID OF CABLE
CONNECTS TO PIN 2 OF DIN PLUG,
CATHODE (K) PIN OF LED3
REAR OF
5-PIN DIN PLUG
(CONNECTS TO CON4
ON MAGNETOMETER)
LED3
K
A
2
4
5
1
3
VR4
3
CW
1
CCW
2
2m LENGTH OF 4-CORE
SHIELDED MICROPHONE
CABLE
UB5 BOX OR SIMILAR
SC
20 1 8
Fig.6: this diagram shows how to wire the DIN plug at one end of the four-core cable,
and the components mounted in the handheld case at the other end of that cable
the reed relay, RLY1. It’s in an IC-type
package and again, it is polarised.
Make sure its pin 1 is orientated as
shown in Fig.5.
Next, fit the MKT or ceramic capacitors (whichever you have chosen to
use). These are not polarised, so you
don’t need to worry about the orientation. Follow with Mosfet Q1 and trimpots VR2, VR3 and VR6. Make sure the
trimpots are fitted with the adjustment
screw in the locations shown on Fig.5.
Solder LED1 and LED2 in place,
pushed down fully onto the PCB, with
the longer anode leads through the
holes marked “A” on the board.
Follow with the electrolytic capacitors, starting with the smallest and
working your way up to the tallest.
These must all be orientated correctly,
with the longer positive leads soldered
to the side marked “+”. The stripe on
the can indicates the negative side.
Don’t get the different values mixed
up; the PCB overlay diagram shows
where each one goes.
Now dovetail two pairs of 2-way
terminal blocks together to form two
4-way terminal blocks and fit these to
the top of the board, with the wire en-
try holes facing towards the edge of the
board. Check they are pushed entirely
down before soldering them in place.
Also fit the fifth 2-way terminal
block at the bottom of the board, with
its wire entry holes facing towards the
two large holes in the PCB.
Having done that, you can also fit
the socket for the pluggable terminal
block (CON5) where shown in Fig.5.
Then solder the fuse holder clips for
F1, ensuring that the fuse retaining
tabs go towards the outside and that
the clips are pushed down flat onto
the PCB before soldering.
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Australia’s electronics magazine
December 2018 33
Next, fit PCB-mounting switches S1S3, again pushing them down as far as
they will go before soldering the leads.
Now bend the leads of LED4 and LED5
by 90° 8mm from the base of the lens,
ensuring that the longer anode lead
(“A”) is orientated as shown in Fig.5,
then solder them to the PCB with the
lens at the same height above the board
to the actuators for switches S1-S3.
Before fitting potentiometers VR1
and VR5 to the board, scrape off some
of the passivation layer from the top
of the pot bodies using a file. Be careful to avoid breathing in the resulting dust.
Solder the two potentiometers in
place, then cut 50mm lengths of tinned
copper wire and solder one end into
the ground hole next to the pots, then
bend the wires over and solder them
to the exposed metal on the pot body.
Finally, solder the DIN socket
(CON4) where shown in Fig.5 and the
PCB assembly is complete.
Testing and calibration
It’s tough to make adjustments once
the unit has been fully assembled, so
it’s best to check that it’s working and
make the required adjustments first.
But you will need to be very careful where you do this and how you
lay the parts out since stray magnetic
fields will make calibration impossible, as will any movement in the components during the set-up procedure.
We recommend that you place the
two coils one metre apart on a sturdy
timber desk – keep them away from
metal in case it is magnetised. Place
the remaining circuitry nearby and
wire it up but make sure that nothing
will move while you are making adjustments.
It’s a good idea to screw the PCB onto
a heavy piece of timber at this stage,
so it won’t move as you work on it.
Use clip leads to short out the two
470k resistors next to CON1 and
CON2 initially, to give maximum sensitivity. Alternatively, you can use a
component lead off-cut to short out
the middle two terminals of CON1
and CON2, to achieve the same result.
Switch S2 on (down) so that T1 is
in-circuit and switch S3 off (up) so that
it is in phase with T2. You can ensure
this by orientating the two coils/transformers identically and making sure
that the same end of each winding
goes to pin 2 of IC1 and IC3.
Set gain adjustment potentiometer
VR1 and trimpots VR2 and VR3 to their
minimum. Fit 1A fuse F1, then apply
power and adjust the presets for channel 1, first VR3 (coarse adjustment) and
then VR2 (fine adjustment), so that red
LED1 only just begins to flicker. Move
a magnet past T1 and check that LED1
flickers in response.
Now adjust Channel 2 using the
same procedure by adjusting VR5
and then VR4, but this time, keep an
eye on blue LED3. Turn up VR5 until
LED3 just lights up, then turn it back
slightly until it goes out.
Use a similar procedure to adjust
VR4.
In an urban environment, depending on the time of day, blue LED3 may
pulsate regularly, indicating that the
unit is overloaded by magnetic flux.
In an environment free from magnetic
noise, it may never indicate overload.
Note that overloading cannot harm the
Magnetometer.
In the unlikely event that you cannot adjust the unit to avoid overloading, you need to reduce the gain of
both channels. The easiest way to do
this is to remove the clip leads from
the 470k resistors next to CON1 and
CON2 (or remove the short across the
middle two terminals, if you used that
approach instead).
You can also replace those
470kresistors with different values;
higher values reduce the sensitivity
while lower values increase it.
As some components in this design
may vary between batches, precise values cannot be offered. Try changing
these resistor values in increments of
around 100k until you find the value which gives maximum sensitivity
without overloading.
Preparing the “case”
As shown in the photos, the prototype was built into a length of concrete
pipe, with sensor transformers T1 and
T2 potted in plastic boxes which were
glued onto the ends.
While this worked well, we don’t
recommend that you use the same assembly technique for several reasons.
Concrete pipes are heavy, relatively difficult to get and may contain asbestos.
Also, you would have to mount most
of the controls off-board and wire them
up with flying leads; a tedious process.
They’re also quite hard to cut and drill;
you need masonry bits for drilling and
a hacksaw with a carborundum rod for
cutting the pipe to length.
In short, while it works, we don’t
recommend it.
The main reason a concrete pipe
was used is that the enclosure has to
be absolutely rigid as any movement
of the transformers will result in false
triggering of the unit.
A metal enclosure is not suitable as
it would interfere too badly with the
small magnetic fields we are trying to
detect. And a plastic (PVC) pipe (even
a heavy-duty one such as a sewer pipe
– would flex too much.
But rather than using a pipe, we
suggest that you build a rectangular
box from 9mm MDF, around 1m long,
with inside dimensions of at least
70x70mm.
If you want to incorporate a sealed
Resistor Colour Codes
Qty. Value
4 1MΩ
4 470kΩ
4 330kΩ
2 220kΩ
11 100kΩ
6 47kΩ
10 10kΩ
1 1.0kΩ
34
4-Band Code (1%)
brown black green brown
yellow violet yellow brown
orange orange yellow brown
red red yellow brown
brown black yellow brown
yellow violet orange brown
brown black orange brown
brown black red brown
Silicon Chip
5-Band Code (1%)
brown black black yellow brown
yellow violet black orange brown
orange orange black orange brown
red red black orange brown
brown black black orange brown
yellow violet black red brown
brown black black red brown
brown black black brown brown
Australia’s electronics magazine
The handheld control unit has a
sensitivity adjustment potentionmeter
(VR4) and an indicator (LED3). This
one is built into a length of PVC pipe.
siliconchip.com.au
This arrangement worked well for our Magnetometer but we have gone off recommending a concrete pipe – not only
because it was really heavy (oh, my shoulders!) but also because these types of pipes (particularly older ones) may
contain asbestos. And that’s a BIG no-no, especially when cutting or drilling holes! The prototype combined S2 and S3
into one DPDT switch (S2) but separate switches may be more convenient (as shown on the circuit diagram).
lead-acid (SLA) battery to power the unit, it may need to
be larger than this.
Having cut suitable pieces of MDF, mark out and drill
holes in one side for the switch actuators, pot shafts, LEDs,
DIN socket and relay contacts (via CON5). We’ve produced
a drilling template which you can download from our website that will help you out. Position this so that when the
PCB is attached to the panel, it will hover just above the
bottom piece of timber forming the case.
You will then need to attach the PCB to the back of this
panel before proceeding, using the potentiometer nuts. If attaching a panel label (a good idea, so you know what control
does what), stick it on first and then screw the nuts on top.
Now sit the timber base up against the side panel and
mark out the locations for the four 3mm mounting holes,
then drill these in the base and attach the PCB using tapped
spacers. Our drilling template is designed to locate the front
panel holes so that 6.3mm tapped spacers are suitable.
We suggest that you feed 25mm long machine screws up
through the base, thread the spacers on, then the PCB on
top and hold it in place using hex nuts. You can now fit
the knobs for VR1 and VR5.
Next, figure out how long the leads going from CON1 and
CON2 to T1 and T2 will need to be. One pair will likely be
longer than the other since that end of the PCB will be closer to one transformer. Cut appropriate lengths of shielded
cable and screw them tightly into CON1 and CON2, with
the shield going to one terminal and the inner conductor
to another (make a note of which goes to which).
Similarly, figure out how long the battery leads to CON3
need to be, cut the twin core lead to length and screw the
conductors into CON5. Feed this cable through the provided relief holes, from the top of the PCB to the underside
and then back to the top again.
Note that you should double check all these connections
since terminals CON1-CON3 may be difficult to reach once
the unit has been fully assembled.
Now would be a good time to attach a carry strap or handle to the top of the enclosure if you want it to be portable.
You can use rope for this purpose but you might prefer
a fixed handle, or you could even fit the unit with wheels.
During operation, the unit should be kept parallel to the
ground. Bear in mind that if you use rope, it will probably
stretch a little due to the weight of the finished unit.
You can now join the MDF pieces together using wood
glue and plenty of small nails or screws, to keep it nice
and rigid.
These will have a slight effect on magnetic fields but
siliconchip.com.au
there are metallic components on the PCB anyway; as long
as everything is held rigidly in place relative to the transformers, they should not cause any false triggering or reduced sensitivity.
Mounting the transformers
While you could build boxes for the transformers from
MDF and mount them on the ends of your main enclosure,
it’s easier to purchase suitably sized plastic cases. You can
then glue the transformers into the cases.
It isn’t necessary to pot them, as was done for the prototype, but you certainly could if you wanted to.
You need to be careful when gluing the transformers
since their windings should be perfectly aligned with one
another, not a fraction of a millimetre out of place.
This is easier than it sounds. A flat floor is all that is required, and a means of ensuring that the coils are perfectly
parallel to one another (say, lining them up carefully with
floorboards).
When mounted, the windings of the transformer should
be horizontal, not vertical, like rings stacked on the ground.
The lengths of the core’s laminations should be perpendicular to the long axis of the enclosure.
The prototype’s sensor transformers were potted to
eliminate any possibility of moisture ingress with the
connections brought out to screw terminals.
Australia’s electronics magazine
December 2018 35
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It may be helpful to keep wires to the transformer windings exposed and accessible, in case you need to change
the wiring later.
Attach the transformer primary and secondary wires to
the wiring that you ran earlier from CON1 & CON2 and if
soldering them, use heat shrink tubing to insulate the joints.
You will also need to connect your battery/battery holder
up to the wires you ran earlier, insert it into the enclosure
and glue it in place. We suggest you use silicone sealant
to do this. Remember that you may have to replace the
battery later.
You can then attach the transformer cases to the ends
of the main enclosure. We don’t suggest you do this using
silicone as it could flex, so use a good epoxy instead (eg,
JB Weld). While you are waiting for that to cure, you can
build the remote control box.
Remote control box
The remote control box contains sensitivity adjustment
potentiometer VR4 and detection indicator LED3 and not
much else. A small Jiffy box (eg, UB3) makes a suitable
enclosure.
As you can see from the photos, these components were
housed in a small section of PVC pipe for the prototype;
you could do the same.
Make holes to mount VR4 and LED3 and another sized to
suit the microphone cable. Attach VR4 using its supplied
nut and glue LED3 and the microphone cable in place using clear neutral-cure silicone sealant.
It’s then just a matter of wiring up LED3 and VR4 to
the cable, as shown in Fig.6. That same figure also shows
36
Silicon Chip
how the 5-pin DIN plug should be wired to the cable at
the other end.
Be sure to secure the strain relief clamp inside the
plug housing around the cable’s outer insulation, to ensure your solder joints won’t fail if there is any tension
on the cable.
Once you’ve wired up both ends, check for the correct
continuity from each pin on the DIN plug to the components in your control box using a DMM set on continuity
mode, then seal up the enclosure and plug the cable into
the socket on the main unit.
You are then ready to test the finished magnetometer
and start using it.
It is recommended that you first ‘play’ a bit with the device to find out how sensitive it is, what it reacts to, and
the best settings for controls VR1, VR4 and VR5.
While experimenting, you should have as few metal or
magnetic materials as possible near the circuit, since these
interfere with its operation.
Experiment, too, with switches S2 and S3, which disconnect T1 or reverse it. A reversed coil pushes the circuit to the limits of sensitivity and is better for long-range
measurements, yet there will no longer be compensation
for magnetic ‘noise’.
Switching one coil out of circuit is useful for experimentation and for detecting the Earth’s magnetic field, by
rotating the unit on its own axis.
Power supply
Power for the Magnetometer comes from a 12V battery
or 12V DC regulated power supply (it must be regulated
since any ripple on the supply line would swamp the small
signals being amplified).
It draws about 150mA during operation. A good-quality 8-cell alkaline battery pack should last a whole day but
note that cheap batteries can fail very quickly with such a
high current drain.
If the magnetometer is to be used often, rechargeable
cells are a good idea. For example, you could use ten NiMH
or NiCd cells (10 x 1.2V = 12V) rather than eight alkaline
cells (8 x 1.5V = 12V).
Or you could use a 12V SLA battery – it should handle this load with no problems and larger SLAs will last
for several days of use. The downside of an SLA battery
would be its weight.
An attractive, and lighter weight, alternative would be a
rechargeable pack made from 4 x 18650 Li-ion cells (3.7V
each). This would give 14.8V – easily within the circuit’s
capability.
Holders for 1, 2, 4 or more 18650s are readily available
and quite cheap – and they give you the option of having
a set of cells in the magnetometer and another on charge.
However, beware of fake or mislabelled 18650 cells – it
has been said that up to 90% of those being sold on ebay,
for example, are fakes. Even some with well-known brands
actually contain dodgy cells with false labels. If the price
looks to good to be true, chances are it is!
Beware of any 18650 which claims more than 4000mAh
(we’ve seen claims of 10,000mAh and more!) – there is no
such cell made. Realistically, 3700mAh is about the highest you’ll find in legitimate cells.
SC
Australia’s electronics magazine
siliconchip.com.au
by
Tim Blythman
So you’ve built a mammoth version of our LED Christmas Tree project from
last month (or at least you’re thinking seriously about doing so!). It’s huge and
has hundreds of LEDs. You want to make the tree do more than twinkle; you
want it to really attract attention! Here is how you can make the most of the
hardware, with some clever software to control it.
Y
ou would have seen our incredible stackable Christmas Tree
project last month. It cleverly
combines many small, low-cost boards
with eight LEDs each to form an illuminated tree of just about any size.
If you’re enthusiastic, it could easily
turn into the biggest SILICON
CHIP project you’ve built, so
we’ve created a program and
some more sample Arduino
code to help you achieve
that and get the best out of it.
The software presented
here allows you to experiment with your tree layout
without having to do any
soldering at all. It will show
you what your tree will look
like (up to a maximum of
ninety-nine boards), and
also tell you the order in
which their shift registers
are addressed.
This program also allows
you to generate Arduino
code (which is of course C/
C++ compatible) to create
patterns based on the phys38
Silicon Chip
ical and logical locations of the LED
boards and individual LEDs within
the overall tree. This means you can
generate patterns such as light radiating up the tree from the base, moving
side-to-side, star bursts or various other geometric patterns.
But wait, there’s more! No, you don’t
get a free set of steak knives. But the
software presented here can also interface to the Christmas LED Tree via the
Digital Interface Module and send it
commands to control an attached tree.
You can click on individual LEDs and
watch them turn off and on in
real time.
You can also use it to generate the commands for a given
illumination pattern, allowing
it to be delivered to the Tree
later, using separate software
(eg, Arduino or BASIC code).
And in case you haven’t
built the Digital Interface Module but have a spare Arduino
board lying around, we’ll present some Arduino code to allow you to emulate some of
its basic features, so you can
use that Arduino to drive your
tree with these more advanced
patterns.
LED Tree Data Map
Program
This application is written
Australia’s electronics magazine
siliconchip.com.au
in the Processing language, which also
happens to be the origin of the Arduino
programming language. If you haven’t
heard of it before, see the panel at right
for more information.
The general idea behind the LED
Tree Data Map Program is that the
graphical interface gives you a virtual
view of your Tree.
You build it by adding tree boards
on top of existing boards, by clicking
on the branch location where you want
to add them.
This is useful both for experimenting to see what size and shape you
want to make your tree but also, once
you have built it, you can create an
identical tree in the software, which
then produces the data you need to
drive its LEDs in various patterns.
Installing the software
We’ve created pre-compiled Windows and Linux versions of the LED
Tree Data Map Program. The Linux
version has been complied for three
platforms: x86 (32-bit), x64 (64-bit)
and Raspberry Pi. All four versions
are available for download from the
SILICON CHIP website.
There is no installation as such; you
just need to extract the relevant executable from the ZIP archive to a folder
on your computer and then run it. But
since Processing is based on Java, you
need to have the Java Runtime Environment installed on your PC to run
the compiled programs.
The easiest way to ensure that you
have an appropriate version of Java
installed is to download and install
Processing.
You can get it from:
https://processing.org/download
We haven’t provided a compiled
Mac version of the software since we
don’t have the hardware to do so. But
if you have a Mac, you can use the Processing software to compile the supplied source code.
You can also use the Processing software to make changes to our software
and re-compile it if necessary. We used
Processing version 3.37 to create and
test the program.
What is “Processing”?
The clever little program we have put
together as part of this article has been
written in a language called Processing.
You may not have heard of it, so let us
explain. . .
Processing is a programming language
which is designed to allow people to easily create visual content. It is an opensource, cross-platform project, meaning
that anyone can get a copy of the source
code and it’s designed to run on a variety
of different operating systems. It can even
run on the Raspberry Pi and some other
single board computers.
If you want to create an app for your
phone or tablet, there’s even an Androidcompatible mode, although we haven’t
tried it ourselves.
We have never really needed to use
its particular features before. But in this
case, being able to create a graphically
interactive and intuitive program was the
deciding factor.
The Processing website at https://
processing.org/ says that it is designed
“for learning how to code within the context of the visual arts”.
While that might seem a poor fit for an
electronics magazine, it happens to suit
us very well since it means that we can
easily depict and manipulate the physical
layout of hardware on-screen.
By the way, the language used in the
Arduino IDE is called Wiring and is built on
the Processing language. If you are familiar
with Arduino programming, you will find
that the Processing IDE (Integrated Development Environment) is nearly identical to the Arduino IDE, apart from the colour scheme.
So it seems Processing has a similar
role in teaching graphical programming
as the Arduino does for teaching embedded programming.
Processing is written in Java and when
it compiles projects into stand-alone executables, they run on the Java platform as
well. This was another reason we chose
processing. While the majority of our readers run Windows, we don’t want to exclude
those who have a Mac or run Linux.
And since we could create a stand-alone
version of our program, you don’t need to
install the IDE to use it.
The language used is Java, which is
similar to C/C++, so programmers familiar
with those languages (or the many similar procedural languages which have been
inspired by them) should have no trouble
adapting.
There are some some small differences;
for example, the #define and #include “preprocessor directives” are not used, but you
can import Java libraries, which we have
had to do to add clipboard functionality to
our program.
Building a tree
When you first open the program, a
single LED Christmas Tree board appears at the bottom of the window.
When you move the mouse cursor
to a location where clicking will lead
to an action, a circle is shown. A large
siliconchip.com.au
The Processing IDE looks very similar to the Arduino IDE. You can even see
some of the language similarities, eg, the ‘setup()’ function.
Australia’s electronics magazine
December 2018 39
Fig.1 (left): when the software is launched, a
single “root’ board is present. Simply left-click
on the location where you want to add another
board and it will appear. Right-click to
remove it. The white dots also indicate which
LEDs have been toggled on by clicking.
Fig.2 (right) : here’s a representation
of the 38-board version from last
month’s front cover. It only takes a minute
or two to set it up. One useful aspect of this
software is you can see whether any boards
would overlap in your design – and you can
even test a tree up to 99 boards in size to see
how it would look.
green circle appears in places where
you can add another branch to the tree
(see Fig.1). As the tree gets bigger, you
can use the “=” (+) and “-” keys on
your keyboard to zoom in and out and
the arrow keys to resize the window.
The program automatically assigns
a number to each PCB, which is displayed on top of that board. This indicates what order the boards receive
data as it passes through the shift registers on each board.
This assumes of course that any unconnected ends have their DO and DI
pins bridged, as explained in the article last month.
You can remove branches (one at a
time) in reverse order by right-clicking
instead of left-clicking. This allows you
to “backtrack” which is handy if you
make a mistake but also useful if you
are experimenting to see which of various different tree configurations is best.
The program assumes that the
boards are simply butted against each
other rather than being spaced slightly as if they were fitted with headers.
But given that you can plan with
precision how the tree will look using
this software, it is well-suited to creating a permanent arrangement, with
the boards joined by short lengths of
stiff wire.
Fig.2 shows the large tree in the introduction of last month’s constructional article re-created in the LED
Tree Data Map program.
Driving the Tree directly
If you’ve built the Digital Interface
Module and have some LED Christmas Tree boards connected to it, you
can control this combination directly
from the LED Tree Data Map Program.
Press the “,” (<) and “.” (>) keys on
your keyboard to scroll through the
displayed serial ports until the port
corresponding to the LED Tree Control Board appears, then press the “s”
40
Silicon Chip
key to connect to it.
The port name turns green if connection is successful. Assuming the
physical layout matches the layout you
have created in the program, clicking
on one LED on the screen will cause
it to toggle on and off, both on-screen
and on the actual board. Of course, if
the two layouts are different, anything
could happen!
A handy feature is that you can press
the “t” key to copy the current state of
the LEDs to the clipboard, from which
it can be pasted into a text editor for
manipulating. This data is in the form
of hexadecimal digits preceded by a
“v” and followed by a “V” to match
the 9600 baud HEX SPI format of the
LED Tree Control Board.
A simple way to use this data is to
paste it into a serial console program
(such as TeraTerm, PuTTY or even the
Arduino Serial Monitor), which will
then send it on to the Digital Interface
Module and on to the Tree.
You could save a number of these
Tree states to a text file in order and
send them to a serial port using an-
other program, or even the following
command from a Windows command
prompt (assuming your file is called
“test.txt”):
copy test.txt \\.\COM30:
Making a map of the Tree
The software does not have any
functions to save an image of the tree
you have created but you can use your
operating system’s screen capture
function to make a copy of the map
once you have settled on a layout. In
Windows, you can do this by pressing
ALT+PrintScreen and then loading MS
Paint (or another image editing program) and pressing CTRL+V. You can
then save the resulting image to a file.
This is a good idea, so that you will
remember exactly where to wire the
boards when you are building the tree
(if you haven’t already).
Pressing the “c” key on the keyboard
copies the current layout information
to the clipboard, in the form of Arduino code. We’ll now explain how that
can be used.
Controlling the Tree with an
Arduino
In the constructional article last
month, we explained how to use a basic Arduino sketch to make the LEDs
in the tree twinkle. But with the code
created using the “c” key, you can do
much more. Once it’s in the clipboard,
the generated code can be pasted directly into a blank Arduino sketch created in the free Arduino Integrated Development Environment (IDE).
If you haven’t used the Arduino IDE,
you will need to download it from the
#define LED_BOARD_COUNT 4
int led_board_rotation[LED_BOARD_COUNT]={0,-1,0,1};
int led_board_depth[LED_BOARD_COUNT]={0,1,1,1};
int led_board_x_coord[LED_BOARD_COUNT]={320,262,320,378};
int led_board_y_coord[LED_BOARD_COUNT]={639,516,490,516};
#define LED_PIXEL_COUNT 32
int led_pixel_x_coord[LED_PIXEL_COUNT]={
331,333,341,348,320,285,300,309,256,234,222,203,173,154,196,234,
331,333,341,348,320,285,300,309,399,424,448,476,465,436,416,390
};
int led_pixel_y_coord[LED_PIXEL_COUNT]={
619,586,561,527,514,521,565,610,495,470,446,418,429,458,478,504,
470,437,412,378,365,372,416,461,510,488,476,457,427,408,450,488
};
Fig.3: sample data generated from a four-board tree. This includes
information about the position of each board and LED in the tree, which the
Arduino (or other) software can then use to calculate which LEDs should
turn on when, to give particular patterns of light.
Australia’s electronics magazine
siliconchip.com.au
Fig.4: the design for
the small nine-board
tree, used to demonstrate some of the
patterns that our
code is capable
of generating.
The program reports
the board numbers in
logical shift register
order, as well as how
many LEDs and boards
are needed for construction.
following link: www.arduino.cc/en/main/software This
program is used to write “sketches”, as Arduino programs
are known, as well as upload them to an Arduino board.
The web page at www.arduino.cc/en/Guide/HomePage
explains the basic workings of the IDE and Arduino-compatible boards. For the examples below, you just need to
load the sketch file, select the correct board type and port
from the “Tools” menu and then click the “Upload” button to test the sketch.
We’ve created a few sample sketches to show how to use
the data from the LED Tree Data Map Program. Fig.5 shows
the wiring required to connect the Arduino board to your
Tree. We used an Uno clone for our tests but these sketches
should work on just about any Arduino-compatible board.
The connections are as follows:
Arduino
5V
GND
D2
D3
D4
D5
ARDUINO
UNO
‘Root’ Tree board
5V
GND
DI
DO
LT
CK
Fig.3 shows the data generated for a simple case of four
boards, with one sub-board connected to each of the three
branch connections on the root board.
The first line, starting with #define, simply tells the program how many boards are in use. This value is also used
to dimension the following arrays which contain information about the location of each board.
The second line defines the “led_board_rotation” array
which contains an integer value for each board indicating
the orientation of the board. A value of zero means the
board is parallel to the root board, while negative values
indicate anti-clockwise rotation and positive values indicate clockwise rotation, in multiples of 45°. So +1 = 45°
clockwise, +2 = 90° clockwise, -1 = 45° anti-clockwise, etc.
The third line defines the “led_board_depth” array which
indicates how far each board is from the root board. The
root board depth is zero, the boards connected directly to
the root board have depth one and so forth. This is a handy
approximation to the vertical position of each board.
The fourth and fifth lines define arrays named “led_
board_x_coord” and “led_board_y_coord” which give the
cartesian coordinates of the bottom middle of each board.
The root board is always at 320,639 with the values ranging from zero up to 639.
Increased x values indicate boards which are further to
the right while decreased y values indicate boards which
are further up.
While these values could potentially be useful in some
cases, most patterns would use the individual LED coordinates which are what is provided by the remainder of
the code.
The second #define indicates how many total LEDs there
are in the tree (which is always eight times the number of
boards) and the final two arrays contain this many integers. Those integers are the cartesian coordinates of each
LED, in order from first to last in the shift chain, using the
same coordinate system as described above for the boards.
Using some simple calculations, you can create some
amazing patterns by checking the coordinate of each LED
and determining whether or not to turn it on, based
on various geometric patterns.
Example sketches
We have provided five sample sketches, to show off some of the patterns that
it’s possible to generate once you have the
data for your Tree.
These are just the starting point; you could
use them as-is or you could expand on them, to
CHRISTMAS
TREE
make even more interesting and spectacular patPCB
terns. You could even combine them into a single
5V
sketch which can cycle through several different
PIN
patterns
over time.
GND
Our first example sketch is named “9_Board_Tree_
PIN
D1
rotate_scan.ino” and it illuminates each group of
D0
PINS
LEDs
in a tree depending on their rotation.
CK
2-5
LT
Although this won’t strictly give a left to right motion if your tree has loops or reverse curves, it still provides an interesting display.
While as the name suggests, it contains the data to
Fig.5: this shows how you can drive the LED Christmas Tree
suit
a Tree made from nine separate boards (as shown
from an Arduino. While we gave a simple test sketch at the time,
this month we’re also providing a general-purpose interface sketch in Fig.4), it is not limited to being used in this way.
You can use it with a Tree made from any number
which allows this configuration to work with our new software.
42
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
of boards in any configuration.
You simply need to replace the coordinate definitions at the top of the
file with those generated from
your Tree design, using
the method described
above.
Nine boards were
chosen simply because we felt that four
boards were not enough
to really show off the
features of this software.
You can change
the data to suit your
tree, of any size, in
each of the five examples
provided.
The code will adjust to
suit your Tree, as it determines the minimum and maximum
values at runtime in the setup()
function.
The second example sketches is
called “9_Board_Tree_depth_scan.ino” and
it first illuminates all the LEDs on the root
board, then on all the boards with depth =
1, then depth = 2 etc.
This gives the effect of light shooting up and out
the tree branches. Its code is virtually identical to the
first example, with just one line changed.
The third and fourth examples are called “9_Board_
Tree_x_scan.ino” and “9_Board_Tree_y_scan.ino”. These
work similarly; the former causes LEDs in the tree to light up
from left-to-right, then right-to-left, creating a vertical line
of light which moves across the tree and it repeats forever.
Similarly, the latter causes a horizontal line of LEDs to
light up from bottom-to-top and then top-to-bottom.
The final example is the most complex and this is “9_
Board_Tree_starburst.ino”, which causes the LEDs in the
middle of the tree to light initially, and then the light spreads
outwards in growing circles.
Saving memory
If you have a large tree, you may run out of RAM to store
the resulting large data arrays.
In that case, you would need to add “const PROGMEM”
to the start of each line defining an array. That will cause
them to be stored in flash rather than RAM.
But note that you will also need to make changes to the
way that the program accesses the data; but we won’t go
into detail on that aspect here.
If you want to see some examples of how to access PROGMEM variables, refer to: www.arduino.cc/reference/en/language/variables/utilities/progmem
General purpose Arduino control board
Finally, we’re providing an extra Arduino sketch which
provides an interface between the LED Tree Data Map Program and an LED Christmas Tree, even if you haven’t built
the Digital/SPI Interface Module described last month.
You just need an Arduino board and some jumper wires.
siliconchip.com.au
It only works with the 9600 baud HEX SPI mode
described last month for the Digital Interface
Module, as there isn’t an easy way for
most Arduino boards to detect the
baud rate their hosts are using. But that’s certainly
good enough to do some
testing or maybe even
drive a Tree in a Christmas display.
Connect the tree to the
Arduino using the same
wiring as the previous example (Fig.5)
and load the sketch,
which is called “Arduino_HEXmode_
Tree_emulator.ino”.
Like the other sketches
provided, it should
Fig.6: this
work on most Arduidemonstrates no boards.
that you don’t
The procedure for
need to be
selecting the serial
celebrating Christmas
to build this project – port in the software
you can turn it into a is the same as described above; use the
Hanukkah menorah
“,” (<) and “.” (>) keys
instead!
to change the serial
[See https://en.wikipedia.
org/wiki/Menorah_(Hanukkah)
port, then press “s”
for an explanation of why it has
to connect.
SC
nine branches.]
MUSICAL
CHRISTMAS
STAR
DIY PROJECT
FROM PICOKIT
SC
Create some holiday cheer
with a DIY Musical Christmas
Star project from PicoKit. This soldering kit has
movement sensing to light some colourful LEDs and play
some Christmas carols.
Optionally, you can upload your own songs with the PicoCODER programming cable from PicoKit (just $15 extra if bought
together with the PicoSTAR).
The PicoSTAR kit is supplied with a pre-programmed
PIC12F510 from Microchip Technology and is compatible with
PicoKit’s own ALPHA Code programming software and coding
with C and ASM languages through the MPLAB-X software from
Microchip Technology.
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December 2018 43
The Mega and Nano
The Arduino Uno is probably the most widely used micro in the world.
We’ve used it in quite a few of our projects. But you may not be aware
of its “little brother”, the Nano, or its “big brother”, the Mega 2560. Jim
Rowe explains the differences between these Arduino variants.
I
n this article, we’ll describe the latest “Revision 3” versions of all three
modules. We won’t mention the earlier versions or other variants like the
Leonardo or Duemilanove.
That’s partly because those other
variants are less popular nowadays
than the three modules discussed
here. Let’s start with the Nano, which
is smaller than and slightly cheaper
than the Uno.
The photos show just how tiny it is,
measuring only 45 x 18 x 18mm. Despite its small size, most of its capabilities are identical to those of the Uno.
In one respect, it’s actually better, offering eight analog-to-digital converter
(ADC) input channels instead of six.
It uses the same CPU as the Uno,
an ATmega328P but it has the 32-lead
TQFP (SMD) package version rather
than the 28-pin DIP version used in
the Uno. Two of those extra pins are
the additional analog inputs.
Like the Uno, it has 32kB of flash
memory, 1kB of EEPROM and 2kB of
static RAM, a RISC instruction set including two-cycle 8x8 multiplication,
23 programmable I/O lines, 32 8-bit
44
Silicon Chip
working registers, two 8-bit timer/
counters and one 16-bit timer/counter
(with prescalers), a master/slave SPI
serial interface and a byte-orientated
I2C interface.
But keep in mind that the Nano’s
small size means that its I/O pins are
broken out to two 15-pin SIL connectors. As a result, it’s not directly compatible with Arduino shields designed
to plug into the Uno. It also lacks the
Uno’s concentric DC power input socket and instead, receives its power via
the mini-USB socket.
There are adaptor shield modules
available for the Nano but it’s best regarded as the Arduino most suitable
for mounting directly on another PCB.
That’s the way we used it in our Brainwave Monitor project, described in
the August 2018 issue of Silicon Chip
(siliconchip.com.au/Article/11185).
Inside the Nano
The full circuit of the Arduino Nano
is shown in Fig.1. This circuit is for
the lower-cost Chinese-made version,
which uses a CH340G chip for the USB
interface instead of the FT232RL chip
Australia’s electronics magazine
used in the US/European version. Otherwise, the two versions are essentially
and functionally identical.
It has a 6-pin header for in-circuit
serial programming (ICSP) or SPI serial bus connections, a reset pushbutton switch (S1) and four tiny LEDs to
indicate power on, serial data transmit/receive and a general purpose/programming indication LED connected
to pin D13 (SCK). These are all identical in function with those on the Uno.
As mentioned above, all the micro’s
I/O pin connections are brought out
to pins on the two 15-pin SIL headers, J1 and J2.
So basically, the Nano can be regarded as a “Bonsai” version of the Uno (or
perhaps more appropriately “penjing”
given its Chinese origin). This, and
its more standard SIL header layout,
makes it better suited for building into
other projects.
The Mega 2560
The Mega 2560 is considerably larger than the Nano or the Uno, at 108 x
53 x 14mm. Not surprisingly, it is also
more capable.
siliconchip.com.au
Fig.1: complete circuit diagram of
the Arduino Nano. The genuine
Nano boards use a FT232RL for IC1
instead of the CH340G shown, but is
otherwise identical.
It uses an ATmega2560 micro, essentially a larger version of the ATmega328P chip used in the Uno and
Nano. It offers 256kB of flash memory
instead of 32kB, 4kB of EEPROM (vs
1kB) and 8kB of static RAM (vs 2kB).
So it has eight times as much flash
plus four times as much EEPROM and
static RAM.
Since the ATmega2560 comes in a
100-pin TQFP (SMD) package, it also
has many more programmable I/O
pins; 86 compared with 23. It also has
16 ADC inputs, compared with six for
the Uno and eight for the Nano.
Significantly, there’s now also a total of four programmable USART serial I/O ports, compared with the single port on the Uno and Nano. Other
siliconchip.com.au
features include four 16-bit timer/
counters instead of just one in the
Uno/Nano.
The ATmega2560 also has a slightly larger set of instructions: 135 compared with the 131 offered on the Uno
or Nano.
Three of the instructions are used to
access and manipulate the extra flash
memory of the ATmega2560. These instructions are EIJMP (extended indirect jump), EICALL (extended indirect
call), ELPM (extended lead program
memory). The last additional instruction (BREAK) is for use with the onchip debugger (JTAG).
But there’s still the on-chip twocycle multiplier, the same set of 32
eight-bit working registers, a master/
Australia’s electronics magazine
slave SPI serial interface and a byteorientated I2C interface.
So the main advantages of the Mega
2560 are the larger memories, the
much larger number of programmable I/O pins and of course the three
additional programmable USART serial I/O ports.
One interesting point to note about
the Mega 2560 is that it’s designed to
be compatible with Uno shield boards.
In effect, all of the extra analog and
digital I/O capabilities are added to
the right-hand end, as you can see
from the photo opposite.
This means that standard Uno
shields can be plugged into the sockets on the left-hand end of the PCB and
they will work normally.
December 2018 45
Fig.2: complete circuit diagram of the Arduino Mega 2560. The
ATmega16U2 (IC2) is used to handle USB communications.
The 6-pin ICSP/SPI header (just to
the right of the main CPU) is also in
exactly the right position to mate with
the socket on Uno shields.
The Mega’s additional USART port
connections are brought out to an extra
8-pin SIL socket at upper right, with the
I2C SDA and SCL pins at the far end.
The analog input connections are
brought out to another two 8-pin SIL
sockets along the bottom right, with
one of these sockets effectively replacing the 6-pin socket of the Uno.
The additional digital I/O connections
are brought out to an 18x2 DIL socket
mounted vertically on the far right of
the PCB.
46
Silicon Chip
So it’s all quite logical and fairly
easy to follow, as well as being almost
100% compatible with the Uno and
shields intended for use with it.
There are also expansion shields
available specifically for use with the
Mega 2560, which take advantage of
its extra capabilities. Banggood has
such a prototyping shield available for
around $6.00, together with a small (17
x 10) breadboard.
Inside the Mega 2560
The full circuit of the Mega 2560 is
shown in Fig.2. We’ve redrawn it from
the official circuit diagrams because
we found these a little hard to follow
Australia’s electronics magazine
in terms of signal flow.
As with most Uno boards, the Mega
2560 uses a separate ATmega16U2 processor to handle USB communications.
This is IC2, shown on the left-hand side
of Fig.2, with the main ATmega2560
(IC1) over on the right-hand side. All
of the circuitry on the left associated
with IC2 is virtually the same as that
of the Uno and that’s also true of the
power supply circuitry at lower left.
As with the Uno, the Mega 2560 can
be powered either via the USB connector (CON2) at upper left or via the
nominal 9V DC input connector CON1,
at lower left. And the circuitry associated with IC7b, Q1 and REG1 performs
siliconchip.com.au
automatic switching between these
power inputs.
Note also that the Mega 2560, like
the Uno, provides a second 6-pin ICSP/
SPI header for IC2, so that it can be
siliconchip.com.au
reprogrammed if necessary. This additional header is marked as ICSP1 in
Fig.2, whereas the ICSP/SPI header for
the main processor is over on the far
right and marked ICSP2.
Australia’s electronics magazine
As with both the Uno and the Nano,
the Mega 2560 has four indicator LEDs.
LED1 and LED2 are connected to pins
11 and 10 of IC2 and show activity on
the TXD and RXD lines used for communicating with the host processor.
LED3 shows when the module is
powered up, while LED4 is driven
via IC7a from the PB7/IO13 pin of
main processor IC1, to allow it to be
turned on or off by program control.
This is precisely the same as on the
Uno or Nano.
Over on the right-hand side of Fig.2,
you can see how all of the additional
December 2018 47
Shown above are the main differences between the Arduino Nano, Uno and
Mega. The prices shown are from https://store.arduino.cc, however, the modules
can be found cheaper elsewhere online
Below: the three Arduino boards shown at close to actual size for comparison.
While the Arduino Mega is directly compatible with the Arduino Uno, the
Nano uses a different pin layout and structure, even though its performance
specifications are identical.
I/O connections of the ATmega2560
(IC1) are brought out to the various
SIL sockets and the 18x2 DIL socket.
The two 8-pin SIL sockets for the
expanded range of ADC inputs are
shown at lower left, with the 8-pin
socket above them for I2C and the RX
and TX lines for the three additional
USART ports (RX1-TX3).
Then above these again there’s the
fourth 8-pin SIL socket and the 10-pin
socket, which basically duplicate the
functions of the same socket on the
Uno: RX0 and TX0, followed by IO215 and then GND, AREF, SDA and SCL.
To the right-hand side of IC1, in addition to its ICSP/SPI header (ICSP2)
there is the 18x2 DIL socket for the ATmega2560’s extra digital I/O pins, plus
two pins carrying the +5V supply line
(pins 1 and 2), and another two pins to
the module’s ground (pins 35 and 36).
So as you can see, the Arduino Mega
2560 is very much an expanded version of the Uno. It has very similar
processing power but with considerably more memory, three additional
USART ports, 10 additional ADC inputs and more than 60 extra digital I/O
lines. It is software compatible with
both the Uno and the Nano.
These features allow it to run much
larger sketches and control more peripheral devices. It’s the Arduino
you’ll probably need for applications
that are too large for the Uno or Nano.
It does cost about twice that of the
Uno but it’s still quite good value for
money when you consider what it offers.
The comparison table above summarises the features of the three Arduino versions we’ve discussed here.
At the bottom of the table, it shows
comparative price ranges for the three
versions but these will vary depending on exchange rates, vendors and
other factors.
Finally, note that Microchip recently purchased their rival Atmel, the
manufacturer of the ATmega chips
used in these boards; hence the links
below to the product pages refer to the
Microchip website.
Handy links
store.arduino.cc/arduino-nano
store.arduino.cc/arduino-mega2560-rev3
microchip.com/atmega328pb
microchip.com/ATmega2560
banggood.com/search/mega2560SC
1280-proto-shield.html
48
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
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$
1195
3195
$
LED DOT MATRIX DISPLAY XC4622
Large 32 x 16 pixel white LED display to
create message boards, clocks, etc.
• 10mm LED pitch
• Can be daisy-chained for larger displays
Follow us at facebook.com/jaycarelectronics
LILYPAD BOARD XC4620
Compact ATMega 32U4 based main board.
A single chip handles main controller
functions as well as USB connectivity.
• 9 Digital IO pins
Catalogue Sale 24 November - 26 December, 2018
Project Of The Month:
STEP-BY-STEP INSTRUCTIONS AT:
jaycar.com.au/strobing-christmas-star
Strobing
Christmas Star:
SEE OTHER PROJECTS AT:
www.jaycar.com.au/arduino
Sticking with tradition and going for the early days of electronics inspired us
to make this kit. Using the traditional 555 Timer IC and a decade counter to
make a strobing Christmas star pattern. Put on-top of the Christmas tree or
just add to your Christmas décor. Add more globes for stunning bright star.
SKILL LEVEL: BEGINNER
TOOLS REQUIRED: SOLDERING IRON
WHAT YOU WILL NEED:
555 TIMER IC
10μF CAPACITOR
1K RESISTOR
10K POTENTIOMER
EXPERIMENTERS BOARD
6VDC 800MA POWER SUPPLY
DC SOCKET
10 x 6V GLOBE
DECADE COUNTER
5 x BC337 NPN TRANSISTOR
5 x BC327 PNP TRANSISTOR
ZL3555
RE6066
RR2774
RP7510
HP9556
MP3145
PS0519
SL2673
ZC4017
ZT2115
ZT2110
$2.25
$0.30
$0.48
$2.50
$4.95
$17.95
$1.95
$1.30EA
$1.15
$0.48EA
$0.48EA
Finished
project:
NERD PERKS CLUB OFFER
VALUED AT
BUNDLE DEAL
$
$49.33
2995
SAVE 35%
FUN TO
BUILD
THIS HOLIDAY
WA S
$
3 9 95
$
4 4.9
WAS $19.95
WAS $19.95
HALF PRICE!
SAVE $7
9
5
$ 95
MINI ELECTRIC MOTOR
EXPERIMENT KIT KJ9032
SAVE $5
PC Programmable
Line Tracer Kit
Demonstrates the basics of how the
magnets, armature and commutator work
together. Ages 8+.
Batteries not
included.
12 95
$
CAN ROBOT KIT
KJ8939
Build wacky robots out of
a coke can, a water bottle
or wasted CDs! 6 robots
to build. Solar powered.
Ages 10+.
KJ8906
An educational introduction to the world of robotics and programming. Use either
programming or line tracing mode. Requires some tools and batteries.
• 120(L) x 64(W) x 55(H)mm
YG2740
KR3160
$
FROM
39 95
WAS $18.95
14 95
$
FROM
18 95
$
SAVE $4
MOTOR CHASSIS ROBOTICS KITS
4 SPEED GEARBOX / AXLE ASSEMBLY
Includes motors, wheels, tyres and two predrilled mounting plates.
• One motor + gearbox per wheel.
• Motor voltage: 5-10VDC
2 WHEEL KR3160 $39.95
4 WHEEL KR3162 $49.95
Features an all plastic moulded gearbox
and motor casing. Includes FA-30 type 3 volt
electric motor, axle with 2 crank arm.
SINGLE YG2740 $18.95
DOUBLE YG2741 $23.95
YG2632
YG2630
FROM
8
$ 95
12
$
95
PULLEY SET YG2869
Typically used to transfer power in a small
energy systems. Set includes 2 x each 50 &
25mm pulleys, 2 x 11mm pulleys, bushings,
screws, nuts and 1m of rubber drive band.
GEAR SET AND SPUR GEAR SET
Gear set contains one pinion gear and two
different sizes of radio gears. Spur gear set
contains three different spur gears.
SPUR SET YG2632 $8.95
GEAR SET YG2630 $9.95
To order: phone 1800 022 888 or visit www.jaycar.com.au
SOLAR EDUCATIONAL KIT KJ6690
WAS $24.95
18 95
$
SAVE $6
CARDBOARD RADIO
CONSTRUCTION KIT KJ9021
Experiment with solar energy - the energy
source of the future. Designed to let you
Make your own AM/FM radio. No
build your own solar models. See website for soldering needed. Requires 3 x AA
inclusion. Ages 8+.
batteries. Ages 8+.
Space Rail
Construction Kit
KJ9001
Build your own marble
rollercoaster with
virtually unlimited track
possibilities! Supplied
with loads of pieces to
make an 11m running
track. Ages 15+.
• Multi-fit baseboard
• 710(L) x 210(W) x 350(H)mm
See terms & conditions on page 8.
GLOWS
IN THE
DARK!
WA S
$
$ 4 9 .9
5
95
39
SAVE $10
51
DIY
PROJECTS
FOR THE
HOLIDAYS
Automate Your Home Or Upgrade Your Home Entertainment:
Digital Keypad
WITH RFID ACCESS CONTROL
LA5353
Suitable to areas requiring stricter
access control such as warehouse,
bank etc. Housed in a sturdy IP65
vandal proof zinc alloy case. Support
up to 2,000 users. Indoor/outdoor
mounting.
• Backlit keypad
• LED indicator (Green/Yellow/Red)
• Built-in buzzer
WAS $69.95
WAS $44.95
SAVE $10
SAVE $10
$
59 95
NON-CONTACT INFRARED DOOR
EXIT SWITCH LA5187
Replace your old push button switch
to this infrared sensor switch to
automatically open the door with just a
wave of your hand. Stainless steel plate
with built-in LED indicator to signal that
the switch has been activated. 12VDC.
• 115(L) x 70(W) x 30(D)mm
$
49
WA S
$
$ 12 9
99
SAVE $30
SAVE $5
SAVE $20
$
BATTERY OPERATED
PHONO PRE-AMP AC1649
MAST HEAD
AMPLIFIER LT3276
A simple 9V battery powered pre-amp used
for connecting products with magnetic
pick-ups such as turntables to an amplifier.
• 2 RCA inputs and 2 RCA out
• 1 x 9V battery required
• 72(W) x 91(L) x 28(D)mm
Powerful boost to provide a quality freeto-air TV signal. Mounts on your antenna
mast, powered by an inside power
injector. Includes mounting hardware.
Indoor/outdoor use.
• High gain amplification
• Full 1080p HD ready
$
LA5077
Upgrade your conventional door
locks to keyless entry/electronic
access. Suitable for narrower
doors. Fail-secure model.
• 12VDC, 450mA
• 160(L) x 25(W) x 28(H)mm
953
952
ZZ8
ZZ8
59 95
SAVE $5
USB2.0 DVD MAKER XC4867
Transform VHS/camera videos into highquality digital recordings! Easily edit and
burn to DVD. Windows™ compatible.
240WRMS
Stereo Amplifier
4
$ 95
50
Z89
SINGLE CHANNEL KEYFOB REMOTE
RFID TAGS
LR8847
Multi-purpose replacement remote control
keyfob for garage doors or security gates.
Single button control. 27MHz transmission.
• Requires 1 x A27 battery
CREDIT CARD STYLE ZZ8952 $4.95
LANYARD TYPE
ZZ8953 $4.95
KEYFOB STYLE
ZZ8950 $5.95
Z
WAS $149
WAS $149
SAVE $20
SAVE $30
SAVE $20
69
119
95
AA0520
Provides crisp audio power with two channels
at 120WRMS each. Ideal for powering a
second set of speakers elsewhere in your
home or office. Dual line audio input.
Remote control included.
• RCA input
• 6.5mm output
• 250(W) x 90(H) x 275(D)mm
WAS $89.95
$
29 95
WAS $64.95
ELECTRIC DOOR STRIKE
FROM
95
WAS $49.95
19 95
$
34 95
$
WAS $24.95
WA S
$ 24 9
19 9
$
SAVE $50
129
$
$
VGA TO HDMI CONVERTER
& UPSCALER AC1718
COMPOSITE AUDIO VIDEO TO HDMI 2.0 4K
UPSCALER CONVERTER AC1776
2 X HDMI TO VGA/COMPONENT & ANALOGUE/
DIGITAL AUDIO CONVERTER AC1721
Ideal for devices with a VGA output (i.e older laptops) to
display on a HDMI device. Also converts analogue audio
source into HDMI digital stream. Plug and play.
• HDMI upscaling up to 1080p
• Analogue audio encoding
• 60(L) x 54(W) x 20(H)mm
A universal converter for analogue composite input to
HDMI 4Kx2K<at>60Hz output. Provide advanced signal
processing with great precision, colours & resolution.
No installation driver required.
• Inputs: 1 x RCA, 1 x S-Video, 1 x USB
• Output: 1 x HDMI
• 93(D) x 84(W) x 28(H)mm
Connect HDMI signals from DVD, Blu-ray or set top
boxes and output to VGA, component video, with digital
(TOSLINK) or analogue (3.5mm stereo) audio outputs for
connection to almost any TV or PC monitor. AC-1721
• HDCP support
• 128(W) x 34(H) x 94(D)mm
Garden Projects to Light Up Your Outdoors:
WAS $19.95
WAS $69.95
WAS $79.95
SAVE $5
SAVE $20
SAVE $20
14
$
4
$ 95
SOIL MOISTURE SENSOR MODULE
XC4604
Automate your garden with Arduino® and
use this module to detect when your plants
need watering.
• Analogue output
• Current less than 20mA
52
95
2 OUTLET 10A POWER
GARDEN STAKE - IP44 MS4097
Versatile and safe way to
distribute power in your garden.
Spring loaded socket covers.
• Water resistant
• 1.8m cable length
• 395(H) x 147(W) x 70(D)mm
$
49
95
$
LED PROJECTION LIGHT SL3403
Light up your home or garden to get
things into party mode! Extremely
bright 4W RGB LED.
• Wave ripple effect
• IP65 waterproof
• 100(W) x 155(H) x 125(D)mm
Follow us at facebook.com/jaycarelectronics
59 95
OUTDOOR LED &
LASER LIGHT COMBO SL3401
Red and green laser with a high power LED.
Includes a mounting stand and garden spike,
as well as a mains power adaptor.
• Remote control included
• 155(D) x 87(Dia)mm
Catalogue Sale 24 November - 26 December, 2018
TECH TALK:
LED Lighting:
Would you like brighter lighting without blowing
the electricity bill? Then an LED (Light Emitting
Diode) solution is what you need. LED lighting has
revolutionised the way we produce light using
silicon technology.
A tiny LED module houses three light sources: Red,
Green and Blue, and combined produce the full
colour spectrum, with brilliant colour affects you
typically see on Christmas trees, shop displays and
flashing lights.
A 5W LED light typically gives off the same light
lumens as a traditional halogen 50W light, which
is a 90% saving in electricity and energy usage
for the same (or better) lighting. LED lighting is
environmentally friendly, and gives off less heat
during operation (making it safer for use in tight
locations).
LED lighting can replace any legacy light bulb
around your home or even your car head
lights. In addition, LEDs come in strips
that can be easily mounted along walls or
cabinets or even wrapped around trees,
to create amazing colourful lighting
effects.
2 FOR
29
$
90
SAVE $10
$
Use for your Laptop,
TV, Wall etc
2 FOR
59
90
SAVE $20
19 95
$
$
Ideal for vehicles, around the
home, or in the workshop
39 95
WATERPROOF LED FLEXIBLE
STRIP LIGHT - 1M ZD0579
Trim down to size to suit your application. Light mode,
colour-change, and on/off controls via inline remote.
IP67 weatherproof. 5-24VDC.
• 1m long USB cable
• 30 LEDs
Fully encapsulated, waterproof & versatile. 1m version
can be daisy chained for longer length. Submersible up
to 1m. IP67 rated. 60 LEDs. 12VDC.
ALSO AVAILABLE:
5M ZD0576 $79.95EA OR
90
SAVE $20
$
$
Display cabinets, under bench
lighting, accent lighting, etc
Can be cut to size to suit your application. Two colour
temperatures available. 12VDC.
• 300 LEDs
COOL WHITE ZD0575
WARM WHITE ZD0577
2 FOR
89
90
SAVE $30
49 95
ea
FLEXIBLE ADHESIVE LED STRIP LIGHTS - 5M
SAVE $$
2 FOR
7990
$
SAVE $20
Great for under
the bed
49 95
MOTION ACTIVATED LED STRIP LIGHT - 1.5M
ZD0588
Create nice bedroom mood lighting with this under bed
light. Contains two long LED strips connected to motion
sensors with 3m activation distance. Warm White. Mains
powered.
• 2 x 90 LEDs.
2 FOR $119.90 SAVE $40
2 FOR
79
$
DEALS!
$
USB POWERED TRIMMABLE RGB
LED STRIP LIGHT - 1M ZD0571
2 FOR
$
Cabinet, Closet,
Aquarium, Festive lighting
59 95
LINKABLE ALUMINIUM LED STRIP LIGHTS - 12VDC
Suitable for caravan, marine, 4WD, auto and domestic applications. Connect multiple
lights together with the included connectors to match your desired length and application.
48 LED 280 LUMENS ST3934 WAS $24.95 NOW $19.95 SAVE $5
84 LED 520 LUMENS ST3936 WAS $39.95 NOW $29.95 SAVE $10
LED STRIP LIGHTS WITH SWITCH - 12VDC
Great for use on window displays, restaurant foyers, showrooms, hotels, and caravan
or RV applications. Four mounting screws are included for fast and easy installation.
48 LED 280 LUMENS ST3930 WAS $24.95 NOW $19.95 SAVE $5
84 LED 620 LUMENS ST3932 WAS $34.95 NOW $29.95 SAVE $5
LED ALUMINIUM STRIP LIGHT WITH SWITCH - 240VAC
Ideal for kitchen, under cabinets, book cases, bathroom lighting
applications. Built-in switch. IP44 rated.
48 LED 650 LUMENS ST3946 WAS $54.95 NOW $44.95 SAVE $10
72 LED 950 LUMENS ST3948 WAS $64.95 NOW $54.95 SAVE $10
To order: phone 1800 022 888 or visit www.jaycar.com.au
SAVE $40
$
RGB LED FLEXIBLE STRIP LIGHT - 5M SL3942
Totally flexible and self-adhesive strip. Allows you to
change the colour to suit your mood, match your shoes,
etc. Trim down to size to suit your application. Remote
and mains power supply included.
• 150 LEDs
2 FOR
13990
$
Used in cinema foyers,
nightclubs, casinos etc.
89 95
RGB LED FLEXIBLE STRIP LIGHTING KIT
WITH EFFECTS - 5M SL3954
An easy to setup RGB LED strip that can produce
an array of dazzling effects. Used in cinema foyers,
nightclubs, casinos etc. Includes 3M adhesive backing,
power supply, remote control, and a joiner to connect
LED strips together. 12VDC.
• 150 LEDs
FROM
19 95
$
SAVE UP TO $10
FROM
19 95
$
SAVE $5
$
FROM
44 95
SAVE $10
See terms & conditions on page 8.
53
18 95
$
WORKBENCH
ESSENTIALS
6
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.
1. LONG BIT SCREWDRIVER SET TD2114
• 22 pieces
• Includes popular slotted, Phillips,Star
and TRI bits
• Storage case include
4
$
29 95
2
WAS $149
119
$
SAVE $30
5
WAS $149
WAS $34.95
SAVE $30
SAVE $5
119
$
$
3
12 95
$
1
3. 1000A TRUE RMS AC/DC CLAMP METER
QM1634
• Ultra-high current 1000A AC and DC
measurement
• Cat III, 6000 display count
• AC/DC Voltage: 750V/1000V
• AC/DC Current: 1000A/1000A
• Carry case included
14
$
39 95
SAVE $15
210 PIECE ROTARY TOOL KIT TD2459
Drill, cut, grind, polish, engrave or sand small
components with ease.
• 32,000 RPM
• 1m long flexible shaft
$
95
6. STORAGE CASE - 19 COMPARTMENT
HB6305
• Made from sturdy ABS plastic
with solid clasps
• Removable compartment trays
• Sizes:
4 compartments: 55(L) x 40(W) x 50(D)mm
8 compartments: 80(L) x 50(W) x 50(D)mm
7 compartments: 110(L) x 80(W) x 50(D)mm
AUTOMOTIVE CRIMP TOOL
WITH CONNECTORS TH1848
42 PIECE ASSORTED SOLDER
SPLICE HEATSHRINK PACK WH5668
• Cut & strip wire, crimp connectors
and also cut a range of metric bolts.
• Comes with 80 of the most popular
automotive connectors
Quickly create sealed soldered joint in one go.
$
129
$
34 95
7 PIECE
SCREWDRIVER SET TD2022
SAVE $5
SAVE $30
PORTASOL® PRO PIEZO GAS SOLDERING KIT
TS1328
• 120 minutes run time, 10 seconds fill,
and 30 seconds heat up
• Maximum 580°C tip temperature
(max 1300°C for built-in blow torch)
• Quality storage case
30%
OFF DIES
TO SUIT
QUICK CHANGE RATCHET CRIMP TOOL TH2000
• Heavy duty ergonomic crimper
• Interchangeable dies, no screwdriver required
• Ratchet mechanism designed for maximum
power or quick release
54
FREE
BUTANE GAS
NA1020
WORTH $4.95
BUY TH2000
AND GET
39 95
Durable, fully insulated screwdriver
set for electrical work. 1kV insulation rating.
• Slotted sizes 2.5mm, 4mm, 5.5mm & 6.5mm
• Phillips sizes #0, #1, and #2
ELECTRONIC
TOOL KIT
TD2117
35 Piece. Multi-purpose
precision screwdriver
set with quality zipped
storage case.
34 95
HB6355
$
WAS $159
29 95
SAVE $5
WAS $39.95
$
5. BENCHTOP WORK MAT HM8100
• Cut, solder, write on it and
not damage your workplace
• Durable
• A3 size PVC
• 450 x 300mm
WAS $34.95
WAS $54.95
$
29 95
2. 300W HOT AIR REWORK STATION
WITH LED DISPLAY TS1645
• Provide more uniform heat transfer and
melt all solder pads at once
• 100-500°C temperature range
• Pushbutton / digital display
• 160(L) x 113(W) x 123(D)mm
4. LED HEADBAND MAGNIFIER
QM3511
• Fits over prescription or safety glasses
• Adjustable head strap
• 1.5x, 3x, 8.5x or 10x magnification
• Requires 2 x AAA batteries
$
39 95
HEATSHRINK PACK WITH GAS POWERED
HEAT BLOWER TH1620
An assortment of 160 heatshrink tubes in 7 different
colours and sizes, plus 1 gas powered heat gun with
Piezo ignition and flame or flameless output.
Follow us at facebook.com/jaycarelectronics
$
FROM
44 95
FOAM INSERT ALUMINIUM CASES
Ideal storage case for most equipment. Foam insert for
complete protection. Lockable. Supplied with 2 keys.
SMALL 407 X 277 X 95 HB6355 $44.95
LARGE 450 X 320 X 145 HB6356 $79.95
Catalogue Sale 24 November - 26 December, 2018
EXCLUSIVE
CLUB OFFERS:
FOR NERD PERKS CLUB MEMBERS
20% OFF
WE HAVE SPECIAL OFFERS EVERY MONTH.
LOOK OUT FOR THESE TICKETS IN-STORE!
COMPUTER
ADAPTORS*
NOT A MEMBER? Visit www.jaycar.com.au/nerdperks
NERD PERKS CLUB OFFER
ONLY $179
20% OFF
COMPUTER
ADAPTORS*
EXCLUS
E
CLUB OFIV
FER
NERD PERKS CLUB
OFFER
E
EXCLUSIV
CLUB OFFER
NOT
A MEM
Sign up NOW BER?
! It’s free to
join.
ONLY $99
Valid 24/7/17 to
BER?
NOT A MEM! It’s free to join.
23/8/17
Sign up NOW
Valid 24/7/17 to
23/8/17
NERD PERKS CLUB OFFER
ONLY $9.95
GAS SOLDERING
& HEATSHRINK KIT
0 TO 30VDC 0 TO 5A
REGULATED
LAB POWER
SUPPLY
TS1115 REG $129
Excellent value
and a handy kit for
those quick and
urgent repair.
MP3840
TL4110
FREE
250G
DIGITAL MULIMETER
FILAMENTS*
SAVE
QM1529*
WORTH
$24.95
$
*Valid with purchase of MP3840.
REG $15.95
1.75mm PLA Filament to suit
3D printers. Various colours
available. TL4110 - TL4122
30
NERD PERKS
NERD PERKS
SAVE
SAVE
SAVE
25%
1W AUDIO AMPLIFIER MODULE KIT
KG9032 REG $9.95 CLUB $5.95
Quick Kit (circuit module only). 56(L) x 16(W)mm.
6 WAY USB POWERBOARD
MS4068 REG $39.95 CLUB $29.95
240V. 6 USB Port.
SAVE
10%
15%
PROFESSIONAL BENCH ENCLOSURE
HB5556 REG $59.95 CLUB $49.95
Aluminium. Ventilation holes.
INLINE RCD CIRCUIT BREAKER
QP2002 REG $34.95 CLUB $29.95
10A. 240VAC.
NERD PERKS
NERD PERKS
NERD PERKS
SAVE
SAVE
HALF
PRICE
15%
30%
CIGARETTE POWER SOCKET WITH DUAL
USB PORTS PS2026 REG $29.95 CLUB $19.95
Marine Grade. 10A Cigarette Power Socket.
10MM M3 TAPPED
METAL SPACERS - PK100
HP0901 REG $29.50 CLUB $19.50
Nickel plated brass.
SAVE
GREENCAP CAPACITOR PACK - 60 PIECES
RG5199 REG $11.95 CLUB $5.95
From 0.001uF to 0.22uF, all 100V.
33 DRAWER PARTS CABINET
HB6330 REG $29.95 CLUB $24.95
Free standing or wall mountable.
NERD PERKS
NERD PERKS
NERD PERKS
NERD PERKS
SAVE
SAVE
SAVE
SAVE
25%
20%
433MHZ WIRELESS MODULES
ZW3100-02 REG $13.95 EA CLUB $9.95 EA
Pre-built transmitter/reciever. 10mA max.
CORROSION BUSTER PEN
NA1410 REG $24.95 CLUB $19.95
120(L) x 14(D)mm.
25%
30%
MODULAR DESIGN NEGATIVE BUS BAR
SZ2011 REG $19.95 CLUB $14.95
Transparent cover with recessed areas. LED
indicator.
NERD PERKS CLUB MEMBERS RECEIVE:
5 CORE TRAILER CABLE
WH3091 REG $39.95 CLUB $27.95
10m length sheathed in a tough black PVC
jacket.
YOUR CLUB,
YOUR PERKS:
20% OFF
COMPUTER ADAPTORS*
NEW OFFERS EVERY MONTH
$1 = 1 POINT,
500 POINTS = $25 JAYCOINS GIFTCARD
*Applies to Jaycar 701B Computer Adaptors: Including D9, D15, D25 Gender Changes, USB A & B, Firewire, DVI adaptors.
To order: phone 1800 022 888 or visit www.jaycar.com.au
6
NERD PERKS
NERD PERKS
30%
$
*Excludes Exotic Filament
NERD PERKS
40%
SAVE
See terms & conditions on page 8.
Conditions apply. See website for T&Cs
55
What's New:
We've hand picked just some of our latest new products. Enjoy!
TECH TALK:
Bluetooth®
$
No more wires, with Bluetooth® wireless technology you are free
to move around while streaming music to your headphones or
speakers up to 10 metres away!
12" Rechargeable
PA Speaker
with Wireless
Microphone CS2497
24 9
$
WC7932
Quick and easy audio output option for your
USB Type-C enabled device.
• Connects to audio input on speakers
or other equipment
• 1m length
$
29 95
8 PORT 10/100MBPS
ETHERNET SWITCH YN8388
$
79 95
PC MONITOR
HANGING CUBICLE
BRACKET CW2834
AA2131
Crystal clear dynamic sound with strong deep
bass reproduction. Built-in rechargeable
battery provides continuous playback up to 14
hours. 3.5mm Auxiliary Jack.
• Built-in Microphone
• Built-in controls
Suits monitors up to 27”
with a standard VESA
mount. Features 360°
rotation, 15° tilt and a
cable management clip
to keep your cables tidy.
Adjustable hang height
for optimal positioning.
Mounting hardware included.
• Monitor Size: 13-27” (33-69cm)
• 120(W) x 330(H) x 99(D)mm
129
$
FRONT
59
19 95
$
Mount your media players, streaming boxes,
mini PCs, Miracast dongles or hard drives
onto the back of your TV or wall bracket.
• Mounting options: VESA, TV wall bracket,
screw, 3M adhesive and hanging mounts
NOISE CANCELLING HEADPHONES
WITH BLUETOOTH TECHNOLOGY
$
USB TYPE-C TO 3.5MM AUDIO CABLE
5-IN-1 UNIVERSAL
MEDIA PLAYER TV MOUNT CW2844
Built-in amplifier and rechargeable battery
perfect for parties, functions or karaoke
nights. Play your music from a Bluetooth®
source, USB flash drive, microSD card or
auxiliary input.
• USB/microSD Playback & Recording
• FM Radio
• RGB LED Light
• Extendable trolley handle & wheels
• 350(W) x 630(H) x 325(D)mm
29 95
95
WIRELESS AIR MOUSE REMOTE
WITH VOICE ASSIST AR1976
Replaces the traditional remote control. Air-mouse
operation to use like a PC mouse but waving in the air or
use the full Qwerty keyboard. Compatible with YouTube,
voice search & Skype. 2.4GHz USB dongle included.
REAR FULL
QWERTY
KEYBOARD
Provides 8 additional ports to an internet
router, firewall, or a standalone network.
Plug-and-play installation and low power
consumption.
FROM
8
$ 95
AUTOMATIC LED
NIGHT LIGHT WITH SENSOR
Automatically switches on and off based on
ambient light. Mains powered. Plug and play.
• SAA approved
2 LUMEN SL3530 $8.95
8 LUMEN SL3531 $9.95
50M 1080P MINI HDMI
CAT5E/6 EXTENDER AC1726
79 95
$
Run your full 1080p HDMI signal up to 50m away.
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SERVICEMAN'S LOG
Travelling makes me go cuckoo
Finally back from a long trip overseas, I
had the expectation of a holiday from my
holiday, but it wasn’t to be. One of the tacky
souvenirs I brought back as a gift was faulty
and of course it needed someone to fix it.
While most people would throw it away, this
was a gift and so I couldn’t help myself and
went straight to work.
On slow days, most of us day-dream
of relaxing in some exotic location,
with nothing better to do but to chill in
the sun and sample the local delights.
Unfortunately, modern travel has
put a wet blanket on those dreams for
me. After far too many hours standing
in queues, lounging about in airports
the size of small cities waiting for connecting flights and being crammed into
aeroplanes packed to the winglets with
irritable travellers, we couldn’t wait to
get to where we were going – whether
far away or back home.
I’ve concluded that this baggageclass travel lark is for other people;
next time it will be business class or
bust!
In theory, technology exists to make
life better but I saw plenty of evidence
to the contrary on my trip. For example, those body scanners at airports.
Not only are they personally invasive
but they are actually slower than the
traditional pat down and metal-detector approach!
On the way out, all the women passengers were diverted from the queue
into and through the scanner, and on
the way back, all the men were. For
those who haven’t had the pleasure,
you walk into a large, walk-in wardrobe-sized metal and glass booth, plant
your feet on two painted footprints
on the floor and hold your hands up
as if surrendering – which of course,
you are.
A back-and-front scanner laterally
rotates around 180° and back before an
image is displayed for the perennially
Dave Thompson*
Items Covered This Month
•
•
•
Fixing a cuckoo clock
Vintage army computer repair
Westminster chimes in Oz
*Dave Thompson runs PC Anytime
in Christchurch, NZ.
Website: www.pcanytime.co.nz
Email: dave<at>pcanytime.co.nz
grumpy operator to view. (Wouldn't
you be grumpy too if your job was to
stare at images of tired travellers' saggy
appendages all day?)
While there is a display outside
the booth that the passenger can view
on stepping out, the security person
barked out orders for me to move forward so sharply that I didn’t have a
chance to see what it looked like before I got a full pat-down anyway. So
what’s the point of these scanners?
For another example, smartphones
are everywhere now. In many parts
of Europe, you can pay for parking,
petrol, souvenirs, groceries or pretty
much anything else just by using an
app, texting a number or holding your
phone near a terminal.
In the airport, you can use smartphones to display online boarding
passes at express check-in terminals
and to pass through the departure and
boarding gates. The express check-in is
great, and a real time-saver, unless (like
us) you have bags you can barely lift
that need to be checked in manually.
However, using the phone for boarding takes longer than when the ground
crew check each boarding pass the oldfashioned way, so where’s the benefit
here to the weary traveller?
On more than one occasion, a passenger couldn’t get the phone to wake
up or the scanner to read it correctly,
holding up those waiting to board even
more. Progress? I’m not so sure.
Enough grumbling. . . for now
Anyway, after two gruelling days
of travel, we were happy to be home,
58
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
and then came all the unpacking. We’d
brought a few souvenirs with us for
friends and family, as one does, and
we’d packed them very carefully to
prevent them from being damaged.
YouTube is full of videos of baggage-handling staff at airports around
the globe casually kicking or dropping
suitcases 15 metres to the ground,
or chucking bags from the hold onto
the trolleys – and sometimes missing. I have no doubt that most airport workers are diligent but even
with our hard-shell cases, we suffered
some damage.
It’s annoying but there it is; we knew
the risks. It is even more annoying
when you unpack something you purchased for someone else, only to find
it doesn’t actually work.
We have an informal but long-standing competition with one couple we
know to bring back the cheesiest souvenir for each other from whatever
country either of us goes to. In this
case, we brought back a small and very
cheap and nasty souvenir cuckoo clock
purchased from a tacky tourist shop at
a famous beer hall in Munich.
This is ostensibly a miniature representation of one of the many cathedrals
dotted around southern Germany that
boast a “glockenspiel”, a mechanical
automaton-style display built into the
clock tower that comes to life on the
hour, every hour and performs sometimes-complex routines in time with
pealing and tolling bells.
We saw quite a few of these displays
from tourist-packed town squares, but
none we saw resembled this souvenir
siliconchip.com.au
version, which includes a tiny, watchsized working clock movement and
a pendulum underneath that swings
back and forward – or at least, is supposed to.
It all looked fine from the outside,
but when I opened the flimsy cardboard box and inserted the two hearing-aid style batteries that came with
it, nothing much happened.
The second hand did advance as expected and the clock ticked away as
cheap movements often do, but after 10
minutes, the hour and minute hands
hadn’t moved at all and the pendulum stayed stubbornly on one side, no
matter how much I helped it to swing.
We couldn’t give this thing away
like it was; no matter how cheap and
cheesy it is, it should at least work. I
had to try to get it going.
But how can one rationalise spending any real time on fixing a $10 trinket? The Serviceman’s Curse strikes
again, of course!
Delving into the clock
Working on it was a bit of a challenge because it is small and oddlyshaped and there is no flat face at the
front on which to lie it down, so I sat
it on a sponge.
The back half is just a plastic frame
but the main body of it is sculpted,
painted plaster with tiny figures inside it, making it relatively fragile. So
I'd have to be careful handling it during the repair.
There are four small neodymium
magnets set into the rear moulding to
hold it to a fridge. These are mounted
Australia’s electronics magazine
on the rear corners of the plastic housing. Inside this plastic frame, I could
see the clear plastic case of the actual
clock mechanism, a very typical cheap
movement likely manufactured by the
millions in some Chinese factory.
Getting to it meant breaking the glue
holding the magnet housing to the
plaster body and this was achieved
with the aid of a craft-knife blade and
a little force. With that housing out of
the way, I had access to the four tiny
screws that held the clock movement
together.
The time-adjusting handle stuck out
from the back of this housing and for
those wondering, I’d already played
around with that in order to get the
hands moving.
While I could manipulate the hands
with the adjuster, they wouldn’t move
under their own steam. It is one of
those systems where you pull on the
adjuster to engage it and twist it either way to move the hands forward
or back, to the correct time.
My thinking was that perhaps the
adjustment mechanism wasn’t clearing the gears when pushed back in and
thus preventing them from moving. No
such luck; even after twiddling the adjuster through the entire range, there
was no hand movement at all. The second hand still ticked away happily but
the time never advanced.
As I had to remove the plastic frame
first, and this housed the pendulum assembly, I decided to check that next.
The pendulum appeared to be moved
by some type of electromagnetic system, an elaborate set-up for such a
cheap device.
The pendulum is simply a painted,
heart-shaped plaster weight moulded
to a short length of silver wire, pivoting at the very top of the plastic frame
and running through a plastic “C” core
which must house coils of wire used
to create the alternating magnetic field.
The problem was that the pendulum
was very stiff, so it stayed where it was
no matter where in the stroke I put it.
I soon saw the problem; the injectionmoulded plastic ‘bearing’ the pendulum pivoted on had come out of its
housing and was sitting slightly askew.
I tried to pop it back in, but it kept
falling back into the misaligned position. I used a bit of pressure to spread
the plastic housing apart and removed
the pendulum assembly entirely from
its mounts and had a closer look at
the pivots.
December 2018 59
Either it hadn’t been made properly
during manufacture, or it had suffered
a catastrophic event in transit, because
one of the tiny pivot pins had mashed
to one side and when I attempted to
straighten it, it broke off completely.
Excellent! This plastic pin looked to
be about half a millimetre in diameter
and about 1.5mm long, so replacing it
would be tricky.
However, I’ve worked on smaller
stuff before, so it was out with the microscope and dad’s old box of teenyweeny drills. I was fortunate to inherit
these drills and blanks when dad broke
down his workshop.
Repairs in miniature
He’d sourced them when he was
making miniature jet engines for model aircraft, using modified car turbochargers for impellers because the
bearings could cope with the expected
100,000 RPM shaft speeds.
He’d needed to make tiny fuel tubes,
mostly from (if memory serves) 1-2mm
diameter brass or copper pipes, which I
think he also made. He’d needed these
drills to bore a series of holes along the
sides of the tube; a tricky task for any
engineer, but he managed to do it.
As different sized holes would
change the engine’s performance, he
drilled many holes in many tubes and
did a lot of experimenting. He’d needed many different-sized drills for this
task and had kept a lot of the blanks
from having the drills made.
These drills were really tiny, some
so small you couldn’t even make out
the flutes until you got them under
a good magnifying glass. They make
my Jaycar set of PCB drills look like
monsters!
I broke out my micrometer and
found one the same diameter as the
remaining plastic pivot pin (0.45mm
diameter) and after trimming off the
remainder of the old, damaged pin
and squaring off the surface with a
craft knife, I used a pin vice with my
smallest chuck to manually drill the
hole where the old pin was.
After going into the plastic block as
far as I dared (probably only a couple of
millimetres), I simply cut the drill off
using a pair of old side-cutters, forming
a new pivot pin. I used a Dremel and
a small cutting disc to very carefully
round off the sharp end of the cut drill,
barely touching it to avoid heating it.
When done, I re-assembled the pendulum into the housing and tried it; it
60
Silicon Chip
now sat square and freely moved back
and forth. Hopefully, the clock mechanism would be as easily fixed.
Onto the next job
I removed the four tiny screws that
held the back of the clock on and it
came off with the adjuster handle
mounted in it. A simple spring arrangement holds the adjuster clear of
the clock’s gears until pulled out to
move the hands. As mentioned, while
the hands do move when adjusted using this method, they just won’t move
any other way.
My guess is there must be something
not making proper contact somewhere
in the movement’s gearbox; a gear must
have slipped out of position or something like that.
The clock movement is a simple
quartz type, with a tiny stepper motor
and a small gear train that moves the
hands. The gears appear to be injection-moulded Nylon, and reasonably
well-made; that is, they are clean and
clearly defined, unlike many cheap
injection-moulded parts.
Individually, they all seem to move
without binding, as demonstrated by
being able to adjust the hands manually, but the problem of why the hands
didn’t move became evident when I
dug in further.
One gear near the start of the train
had several teeth missing, perhaps
faulty from manufacture or more likely eaten off due to the clock running
with the hands stuck or the adjuster
preventing gear movement.
When I advanced the gear to where
there were some teeth, the hands
moved as expected, but soon stopped
again when the gear came around again.
This was the worst-case scenario, as
while I have a parts bin full of gears
and small cogs recovered from old
clocks, printers, scanners, video recorders and various other contraptions
over the years, I had nothing remotely
like this gear in there. To repair this
clock, I’d either need another suitable
clock mechanism to replace this one,
or a 3D printer and a plan of the gear;
none of which I have.
I hate being beaten by anything, let
alone something as seemingly insignificant as this but it happens all the time,
at least in my serviceman’s world; perhaps I should have paid more attention at school.
There are always jobs where I discover there are no circuits or parts
Australia’s electronics magazine
available, or the manufacturer has intentionally obfuscated components,
making them next-to-impossible to
identify and replace, yet every time
it happens it is still a bitter pill to
swallow.
There is nothing worse than a run
of jobs that don’t have positive outcomes, and it transpires that this one
will stay broken as well. It’s a shame
that after all this we can’t give it to our
friends, so after gluing it back together, it now hangs on our fridge. We had
to give them another cheesy souvenir
that we had (luckily) also purchased
when overseas.
At least the clock sounds like it is
working and the pendulum goes back
and forth. That is a fix that I am quite
proud of. I’ll take the win no matter
how ridiculous it was to do it.
Even though the clock doesn’t work,
at least it shows the correct time twice
a day!
Military computer repair
These days, if you have a problem
with your computer hardware, there
are all sorts of diagnostic tools to help
you figure out what is wrong.
That wasn’t true back in the 70s
though; most computers were too expensive and specialised. G. C., of Briar
Hill, worked for the Australian Army
when he ran into the dreaded intermittent fault with a computer they were
evaluating...
In the late 1960s, the Australian
Army was investigating the possibility
of using a computer system to quickly
and accurately calculate the angles required to aim artillery guns.
A “paper evaluation” concluded
that a British Army computer had features more suitable for the Australian
Army than those of a similar computer
used by the American Army.
So an arrangement was made for one
of the British computers to be evaluated by the Australian Army.
Rather than sending out a British
Army technician to look after the computer while it was in Australia, it was
cheaper to send an Australian Army
technician to England, to be trained
on the equipment.
I believe the arrangement was between the Australian Government and
the manufacturer, Elliott Automation;
the system that came to Australia didn’t
belong to the British Army.
In 1969, I was selected to go to England to do the three-month course on
siliconchip.com.au
the maintenance of the Field Artillery
Computer Equipment (FACE) at the
British Army’s School of Electrical
and Mechanical Engineering (SEME).
The equipment, along with diagnostic equipment and many spare parts,
arrived in Australia in 1970. I then
became intimately associated with
the system, working with it for more
than a year.
The system comprised six major
pieces with many interconnecting
cables. These pieces were: the operator’s console, the computer, a program
loading unit, a teleprinter, a DC-to-AC
inverter (to power the commercial
teleprinter) and a power distribution
module.
Due to the short length of one specific cable, the computer was mounted
upside-down on the trolley which was
built to hold the lot.
A team of Australian Army Artillery personnel had been trained in
the use of the system and it was then
taken all around Australia, to various
Artillery units, to show it off and to
have its usefulness evaluated. I went
along with the system, to make sure it
kept working.
It worked flawlessly for about six
months, then it developed an intermittent fault.
The fault showed up as an error code
displayed on the console and the code
(9000 from memory) indicated that it
was a fault in the computer, but not
what the fault was.
The computer was an Elliott 920B,
which was a lighter weight but ruggedised version of their 920A computer.
This was used, among other purposes,
to control traffic lights.
As I had been trained on the test
equipment, I figured that I could easily find the fault. The main piece of
diagnostic equipment was the computer test set.
All I had to do was undo some of the
cables going to the computer module,
connect other cables to the computer
test set and start the test.
A slight hiccup: some of the points
the test set needed to monitor didn’t
appear on any of the pins of any of the
external sockets of the computer, so it
had to be opened up and two smaller
cables then connected to the internal
points. Simple, except that there was
the main cover to be removed then an
internal electromagnetic shield.
The cover was no problem, only
20 large screws to undo. The shield,
though, had 64 screws holding it in
place. And this was in the days before
we had electric screwdrivers. It took
about half an hour just to get the test
set connected.
Once the cover and shield were removed, two printed electronic circuit
(PEC) cards had to be pulled out and
re-installed using extender PECs. The
two smaller cables were then connected to sockets on the extender PECs.
The testing with the computer test
set was all logical; it tested computer
functions (circuits), in a specific order,
and then used the tested functions to
extend the testing.
It had many rotary switches and
these had to be switched in specific
sequences. At each step I compared
the results, shown on nixie tubes, to
values in a table in the repair manual.
The complete test took about an hour.
The first time I did this test to find
what the 9000 error code was actually about, the test set indicated that
no fault was found. I reckon that I repeated the test about six times and it
didn’t find any problems.
I disconnected the test set, put the
shield and cover back on and re-connected the system. Everything worked
correctly; no error code appeared on
the console.
The system worked for another
month or so, then it did it again. I
repeated the test and still, no fault
showed up. This happened once or
twice again and each time, some sequence in the testing seemed to clear
the fault before it could be detected.
Then the fault started to occur more
regularly and I was getting a “bit of
stick” from the operators for not being able to fix the equipment.
I was beginning to think it was a heat
related problem, and that by opening
the computer up, the cooling cured
the problem. To prove this, when the
error code next appeared, I closed the
system down and left it overnight to
cool down.
The photo above shows the teleprinter at left and operator’s console being used, with a labelled diagram at right. This
computer used a ferrite core system for memory with a total capacity of 147,456-bits. Refer back to the article in Silicon
Chip, March 2014, for an explanation of core memory (siliconchip.com.au/Article/6937).
siliconchip.com.au
Australia’s electronics magazine
December 2018 61
The Field Artillery Computer Equipment,
with the Elliott 920B in the foreground.
The next morning, the error code
showed up immediately the system
was switched on. Only running the test
sequence cleared the problem.
So, I tried to overheat the system to
get the unit to fail completely. With
the computer opened and the test set
hooked up, I had a vertical bank of
two-bar electric radiators pouring heat
into the computer; still, it didn’t miss
a beat on the test set.
Finally, the error stayed and going
through the test sequences with the
test set didn’t cure it. But worse, the
test set didn’t identify what the problem was.
I got permission from the Australian
agents of Elliott Automation to contact
their head office, in Britain, directly.
The quickest way to make contact, in
1970, was to use the Defence messaging system. This was a teletype system.
Elliott Automation had a British
Army message centre on their premises, so I could compose a message directly to them.
I would write out what the problem
was and what I had done and submit
the message to an Australian Army
message centre. They typed it up on
their teletype system and sent it over
the submarine cable to Britain.
Due to the time difference, I usu-
ally had an answer back when I got to
work the next day. This was kept up
for about a week, with their engineer
telling me what to try next.
I’d write up the results I’d found in
another message before leaving work
for the day and have a reply by the next
morning. Most of their suggestions involved exchanging various PECs in the
computer with a spare.
The people at Elliott Automation
must have sensed that this slight problem may be about to put the kybosh
on the sale of the FACE systems to the
Australian Army.
The engineer asked me, by message,
did I have a home telephone that he
could call me on? No, I didn’t, and the
Army unit where I worked had closed
for the day by the time the engineer
was at work in England, so I couldn’t
stay back to talk to him. What I did
have, though, were parents-in-law
who had a home telephone.
I arranged for the engineer to call
their number at about 8:00pm Australian time and I’d be there to talk to
him. This we did for about three days
and nothing he could think of worked.
“I’m coming out,” he said, and he was
there in Sydney in about three days.
He observed the fault first hand and
stepped through the test procedure,
many times, getting the same result
as I had. The test set was not finding
the fault. His analysis was that it was
a fault in the computer memory. This
was the only item for which a spare
hadn’t been sent out with the system.
The computer memory was a ferrite core system, with 147,456 ferrite
doughnuts being the storage medium.
Its capacity was 8192 18-bit “words”.
The engineer then brought out the
“big gun” from his luggage, a computer programming keyboard. We
hooked it up directly to the computer;
the keyboard had its own display. Because I had been taught the computer
“language”, its instruction set, on the
course that I had attended, he told me
to write a program to test each bit of
each word of the memory.
So, I tried writing all 1s to each bit
Westminster chime clock repair
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.
J. H., of Nathan, Qld, ran into his
own clock problems, with a custom
part being faulty. However, his story
turned out better than expected...
As children growing up in the 40s,
both my wife and I lived in households
which had a Westminster chimes mantle clock. So as a special gift for my
wife’s birthday I presented her with a
Napoleon’s Hat Westminster Chimes
clock. The clock has given wonderful
performances for twenty years. The
quartz movement gains so little time
that the clock does not need resetting
between battery changes.
However, just recently, the clock
lost its chime function and because of
the sentimental value attached to this
clock, I thought I should try to repair it.
The clock consists of two sections
– the quartz movement powered by
a 1.5V alkaline cell and the chimes
section, independently powered by
Australia’s electronics magazine
siliconchip.com.au
Servicing Stories Wanted
62
and reading the bit back straight away.
All good. Then I tried all 0s, still good.
Then he suggested a chequer-board
pattern, writing “10101...” (18 bits) to a
location and test it straight away, then,
if good, write “01010...” to the same
location, read it back and, if good, go
on to the next location.
Well, that did it! Finally, the fault
showed up as one bit that didn’t
change to the appropriate magnetic
state when it was being programmed.
The fast changing of the magnetic
state of that one ferrite core with the
chequer-board program identified the
problem. The computer test set didn’t
perform such a test.
A hasty message was sent back to
Elliott Automation and a new memory unit was dispatched and it was in
Sydney within a week. “These memory units never fail, that’s why there
was no spare sent out with the equipment,” the engineer told me, “they are
ultra-reliable.”
They were also very expensive. The
cost of all the other spare parts sent
with the computer was insignificant
as compared to the cost of one ferrite
core memory unit.
The evaluation of the FACE system
continued, once the new memory unit
was installed, and the Army went on
to buy many of these systems.
A representative of Elliott Automation told me later that the ferrite core
in the memory unit that failed had a
microscopic crack through it.
Silicon Chip
two 1.5V alkaline cells in series. Two
wires run from the movement to the
chimes section and, on the hour, the
movement shorts these two wires
which then triggers the chimes section to start the hourly chiming and
tolling sequence.
The faulty chimes unit consists of
an epoxy-encapsulated IC about the
size of a 10¢ coin which drives a tiny
4cm speaker.
The speaker tested OK but there was
no way that the epoxy covered IC could
be repaired. An internet search for a
possible replacement revealed that
they cost about $US30, with about as
much again for postage.
One clock company in the USA had
a replacement for about $US8 but the
postage was a secret. I emailed them
three times for the total cost including postage but never once received
a reply.
Determined not to be beaten, I had to
fall back on my own resources to effect
a repair. Surely, I thought, it wouldn’t
be too hard to get a microprocessor to
play the simple Westminster Chimes
tune and then add the appropriate
number of tolls. There are only four
or five notes involved.
I had some older mark 1 Micromites
on hand so I used one of the pulse
width modulation (PWM) outputs to
generate the required frequencies and
experimented with the duration and
pausing between notes until I had a
respectable melody.
I used the two wires from the movement signalling the hour to wake the
microprocessor from sleep mode,
whereupon it would play the chime
and toll and then go back to sleep. For
good battery life, not only did I use
sleep mode but I also set the CPU to
run at its slowest possible speed. Also,
I set the chimes to cease at 10pm and
resume at 7am – as much as I like a
chiming clock, the friendship ceases
at 10pm.
The new circuit was able to fit (just)
into the space vacated by the original IC and as I assembled the clock, I
thought I had solved the problem. But
it was not to be. After a few hours listening to the chimes, I realised they
weren’t Westminster chimes at all!
Where were the bells? The square wave
PWM output was just so mechanical
and un-musical.
Well, I thought, maybe I could make
the sound more interesting by adding
a second PWM channel with a note
siliconchip.com.au
separation of about 8Hz from the first
to create a vibrato effect on the note.
This did make the sound more interesting but it still sounded like the Westminster Chimes played on bagpipes!
So I put the clock back together
again with its bagpipe sound but I
knew this wasn’t the end. Maybe I
would get a reply on that unit from
the USA?
It was sometime later that I came
across the DFPlayer Mini. This device is a 16-pin miniature MP3 player
module measuring about 20 x 20mm.
With its own 3W audio output stage, it
can be configured to play MP3 tracks
stored on a microSD card either by a set
of momentary contact switches or by
commands sent from a microcontroller via a serial port (see the El Cheapo
Modules article on page 74 for details
on this module).
I had already seen websites from
which the full set of Westminster
chimes could be downloaded in MP3
format. I had played some of these on
my computer and they sounded impressive. So here was the solution to
my problem. A ménage à trois of the
DFPlayer, a set of MP3 chimes on an
SD card and a Micromite.
It took four weeks for the DFPlayer
Mini to arrive from China but in that
time, I was able to build a circuit on
Veroboard, ready for the module to be
dropped in.
I also prepared and tested a suitable
program for the Micromite. The original clock only chimed on the hour
but not on the half or quarter hours.
As mentioned previously, the hourly
chime was synchronised by the two
leads from the clock being shorted
together.
But now that I had a full set of
chimes, I decided to make my program
Australia’s electronics magazine
incorporate the half and quarter hour
chimes also.
The hour chime is fully synchronised to the quartz clock but the half
and quarter chimes would have to rely
on the Micromite’s internal clock. As
the Micromite’s internal clock is not
very accurate over the long term, it is
reset by the program to correct time
on the hour as determined by the
quartz clock.
The DFPlayer finally arrived and all
was ready to go when disaster struck!
As I was unsoldering the previous set
of leads from the clock’s tiny loudspeaker, to connect it to the DFPlayer
outputs, the loudspeaker’s terminal
connection pad completely separated
from the frame.
A quick examination of the fine
leads going to the loudspeakers coil
verified that repair would be impossible. I had some small 6cm speakers
salvaged from old computers but they
were too big for the allocated space in
the clock. So to test the new chimes
circuit, I pressed into service a larger
12cm speaker. This speaker is the type
usually seen in a car’s audio system on
the rear parcel shelf.
And what a surprise – with this new
bigger and better speaker the clock
sounded like Big Ben itself! It wasn’t
a disaster after all. I decided to mount
the speaker on the rear of the clock – it
just fitted neatly but I would now have
to remove it every time the clock’s battery needed changing.
Also, the power requirements meant
that the chimes could no longer be
powered from a 3V battery source. I
had to use a 5V plugpack supply instead. But this was a small price to pay
for such a fantastic outcome. Gone are
the tinny sounding chimes and gone is
the bagpipe wielding Scotsman. SC
December 2018 63
CHRISTMAS SHOWCASE
MS46121B Compact
1-Port USB Vector
Network Analyzer
CHRISTMAS STAR –
Special offer for
SILICON CHIP
readers.
Looking for something different
this Christmas? How about this
build-it-yourself musical
Christmas Star from PICOKIT?
Supplied with a pre-programmed PIC12F50 which
not only controls the LED chaser pattern, it also has five
popular Christmas carols which play in sequence and
in sync with the 20 ultrabright wide-angle LEDs. It can
even be controlled by motion with infrared motion detection.
Normally great value at $24.20, for a limited time
SILICON CHIP readers will pay only $18.70 – a 22% saving!
You’ll find more information on the PICOKIT STAR
on the PICOKIT website (see below)
PicoKit - Maker Space Solutions
Upper Caboolture 4510, QLD
Phone: 07 5330 3095
www.picokit.com.au
$AVE
$20
The Aussie-made
modular hearing
aid is sweeping
up awards
You might remember Ross Tester’s review of Facett, the modular hearing aid by Blamey Saunders Hears, from the April edition of SILICON CHIP.
Ross said, “The construction and battery connection is highly innovative. And they look pretty fancy too…”
Since that review, Facett has received 12 awards for innovation and
design, including the prestigious Australian Good Design of the Year
Award and the CSIRO Design Innovation Award.
Facett solves big issues preventing people from using hearing aids cost, stigma, and usability. Here are a few reasons it’s winning awards:
It’s made for easy handling
Facett uses silver-zinc rechargeable batteries housed in disconnectable modules which attach instantly, magnetically, to the hearing aid
core (DSP).
It enables affordable upgradability
Instead of buying a new hearing aid model, Facett users can access
new features by buying add-on modules that work with the original core.
It’s user-programmable
The award winning IHearYou® app lets users control their
listening preferences and program the hearing aid
themselves, on a smartphone, tablet or computer, with
the same software used in clinic by Audiologists.
For more, visit facett.com.au
64 Silicon Chip
The MS46121B is
a series of two PCcontrolled 1-Port USB
ShockLine Vector Network
Analyzers with frequency ranges
of 40MHz to 4GHz and 150kHz to 6GHz. The MS46121B provides
performance and accuracy for your one port measurements in a
low cost and space saving solution that is small enough to directly
connect to the device under test. All the members of the MS46121B
series are aimed at RF and microwave applications in manufacturing, engineering and education. The two MS46121B options both
come with 120 microsecond per point sweep speeds and a measurement accuracy of ±0.5dB (-6dB offset, typical), making them
suitable for your passive device test applications.
These new very compact VNAs are externally controlled via
USB from a user supplied PC. Up to 16 independent MS46121B
VNAs can be operated in parallel from the same computer running
ShockLine software. This enables true parallel multisite testing of
1-port devices improving throughput over traditional single VNA
and switch matrix test solutions.
Web: www.anritsu.com/en-AU
Email: AU-sales<at>anritsu.com
Part No.
IMG6021
ON THIS PRO-QUALITY
MAGNIFIER FROM
WAGNER ELECTRONICS
This professional laboratory grade
magnifier boasts a 5” (127mm) glass lens
with 3 dioptre magnification.
Heavy duty, covered springs in the arm
allows for easy manoeuvring with minimal force.
The mag is surrounded by 60 high efficiency LEDS producing a maximum output of 850lm. What makes this magnifier unique is that the colour temperature of the LEDs are
adjustable from 3500K to 6500K allowing the user to adjust
the output to suit the environment or product being viewed.
Supplied with a heavy duty clamp which allows the magnifier to be attached to a desk and a mains power supply is
included
RRP is $139.00 – however as an introductory special, for
a limited time only the price has been reduced to $119.00.
Wagner Electronics
84-90 Parramatta Rd, Summer Hill, NSW 2130.
WEB: WAGNERONLINE.COM.AU Phone: (02) 9798 9233
Australia’s electronics magazine
siliconchip.com.au
CHRISTMAS SHOWCASE
Launch of the Alternative
to Dow Corning’s CN-8760
Encapsulant
43” 4K
HDR1000
Brilliance
Monitor
These days
computer monitors
are about more
than just computers.
With 4K resolutions, multiple HDMI connections
& remote controls they can be used to display almost
any content from game consoles to Chromecasts.
This Christmas Philips have paired a huge 43”
4K panel with HDR1000 capability to deliver the
ultimate versatile display.
Finish your spreadsheets and then fire up the
Netflix before strapping in for a night of hard-core
gaming.
You can do it all on them Philips 43” 4K HDR1000
Monitor.
Right now get a $100 Cash Back on this model
available for a street price of around $1400
Electrolube, global electro-chemicals manufacturer has
recently formulated and launched a brand new thermally
conductive encapsulation resin. The product (SC4003) has
been specially developed to fulfil user requirements for a
low viscosity, thermally conductive encapsulation resin with
a wide operating temperature range.
The user in question initially expressed an interest in Electrolube’s encapsulation resins for an LED based application
but listed some specific requirements including a room cure
system, a temperature range of -60 to +200°C and thermal
conductivity of 1W/m.K. The customer also specified a requirement for a low viscosity system with good flow characteristics that would easily facilitate the potting of difficult and complex geometries and ensure minimal stress on
components.
Phone: (02) 9938 1566
Web: electrolube.com.au
Three new
Spectrum Riders
from R&S
THIS CHRISTMAS,
CAN REPLACE OR REBUILD YOUR
ELECTRIC BIKE BATTERY
(or any other battery!)
Got an e-bike with sick (or dead!) batteries? How about
a mobility scooter, wheelchair, golf cart . . .
Premier Batteries can assist you with batteries – New
and Reconditioned – which will get you going again.
For 500 watt, 1000 watt and 2000 watt models.
Premier Batteries are specialists in Battery refurbishment. They can supply new or recell e-Bike or other
batteries with High Quality Cells – often with higher capacities than the original.
Premier Batteries can replace, repair or refurbish rechargeable batteries for just about anything. Call them
now before the holiday season.
PREMIER
BATTERIES
PREMIER
BATTERIES
Unit 9, 15 Childs Rd, Chipping Norton NSW 2170
High quality batteries for all professional applications
Ph:
(02) 9755
1845 BATTERIES
Web: premierbatteries.com.au
SUPPLIERS
OF QUALITY
FOR OVER 30 YEARS
Email: info<at>premierbatteries.com.au Web: www.premierbatteries.com.au
siliconchip.com.au
Rohde & Schwarz has expanded its
successful R&S Spectrum Rider FPH
family with three new base models providing frequency ranges from
5kHz to 6GHz, 13.6GHz and 26.5GHz.
The R&S Spectrum Rider FPH was the industry’s first handheld
spectrum analyzer to offer a capacitive touchscreen and a unique
frequency upgrade concept via keycodes. Since upgrades require
neither downtime nor recalibration, users can effortlessly upgrade
their base models, eg, from 26.5GHz to 31GHz.
New higher-frequency models enable the rugged R&S Spectrum Rider FPH to perform a vast range of measurement tasks in
the field and lab. The R&S Spectrum Rider FPH is a handy tool for
diverse applications, such as verifying signal transmission over
5G, broadcast, radar and satellite communications links.
The 2.5kg, battery-operated instrument will appeal to field
technicians and lab engineers alike, as it supports everyday
measurement tasks in aerospace and defense, mobile network
testing and broadcasting, as well as tasks to be performed
by regulatory authorities and tasks in education.
See more: www.rohde-schwarz.com/spectrum-rider
Unit 9, 15 Childs Road
Contact:
Mark Fisher at Rohde&Schwarz
Chipping Norton NSW 2170
Ph: 03 8544 8300
Tel: 02
9755 1845
Email:
sales.australia<at>rohde-schwarz.com
Australia’s electronics magazine
December 2018 65
Des
Design
by
Les Kerrr
Article by
Les Kerr &
Ross Tester
A Christmas project
that will keep the grandkids
entertained well into the (2020?) New Year!
SILICON CHIP projects don’t all have to be serious, nor solve one of mankind’s
greatest needs, nor even be all that practical. Some of them are whimsical;
others – like this one – can be downright useless! Nevertheless, it’s all good fun!
Y
ou’d remember the Pet Rock
craze from a few years ago? The
ultimate Useless Box would be
just like one of those – that does absolutely nothing.
But we wouldn’t mind betting that
kids would get sick of a box that does
66
Silicon Chip
Froggy just sits there, minding his own
business . . .
nothing even faster than a pet rock!
This Useless Box doesn’t lose any
of its “uselessness” but it actually does
something: if you disobey the instruction on the front and turn it on, it turns
itself off again!
Now you’d have to agree that this
Australia’s electronics magazine
Uh-oh, someone has operated the
switch! The lid flies open . . .
is close to, but not quite, totally useless . . .
The Useless Box has one switch on it
with a simple label: Don’t Operate The
Switch – which, of course, becomes
overwhelmingly tempting for just about
anyone – especially young children.
siliconchip.com.au
The light comes on and Froggy’s hand
(foot!?) comes up out of the box . . .
But why don’t we start at the start
– the Useless Box obviously needs
a box!
The Useless Box box!
Something chirping inside the box
adds to the intrigue and eventually
curiosity gets the better of them – and
they give in and flick the switch.
The box whirrs, its lid opens, a light
comes on, a frog (yes, a green one!)
pops out and his “hand” reaches out
to turn the switch back off again, with
a warning not to touch it again. “GO
AWAY!” it says. (The frog’s mouth
moves in time with its “speech”).
After which, the frog goes back inside the box, the lid closes . . . and
that’s it – until next time the switch
is operated (which, of course, it will
be before long!).
After this, the frog even gets a little
aggro, throwing the lid open a couple
of times and closing it, with a final
“I TOLD YOU TO GO AWAY!”
siliconchip.com.au
And reaches over, pushes down on the
switch to turn it off . . .
So that’s the Useless Box – a great
gimmick to build for a Christmas present, particularly for the grandkids.
(In fact, that is why the Useless Box
came into being).
It will keep enquiring young minds
amused for hours, wondering how
Froggy knows that they’ve disobeyed
his warning and how he pops out and
turns the switch off again!
Just in case you’re still wondering about the hows/whens/wheres/
whys of the Useless Box, we’ve
made a small video of it so you
can see for yourself. You’ll find
it at siliconchip.com.au/Videos/
Useless+Box
Australia’s electronics magazine
He utters a few words while the light
turns off and he slinks back inside . . .
We used a hinged jewellery box
which we obtained at a local bargain shop – ours measures 200mm
x 150mm x 110mm but the dimensions aren’t particularly important,
just as long as it can house the internal workings.
You may find one slightly different
– or, indeed, you may put your handyman skills to work and build your own.
Box material is also unimportant –
any lightweight timber will do, as long
as its made strong enough to handle
many openings and closings. A lot
of the commercial ones appear to be
made from bamboo or craftwood.
It’s nice if the top and bottom of the
box are a tight fit when closed, too –
you don’t want to give any clue about
what’s inside box before inquisitiveness gets the better of them and the
switch is flipped!
For all the above reasons, we
haven’t shown any drawings of the
box. What we have shown is several
photos of the frog and the box internals, which you can follow when crafting your own.
We’ll get back to these shortly.
The frog’s arm
The most important part of the mechanical design is the frog’s arm.
It is U-shaped and attached to a
servo so that when rotated through
180°, it extends over the front edge
of the box and presses down on the
power switch, toggling it.
You can see the arm both in its resting position and reaching out to turn
the switch off in the photos of the box
internals.
The photos also show an aluminium
bracket on the lid which holds the lid
closed when the frog is chirping.
This is so that the children can’t
December 2018 67
And waits for the next person to ignore
the warning and operate the switch . . .
+12V
D1 1N5405
A
REG1 7805
100 F
0V
+5V (FOR SERVOS ONLY)
OUT
IN
K
GND
REG2
LP29 5 0-5.0
IN OUT
+5V (FOR FROG CIRCUITRY)
GND
100nF
100nF
100 F
4.7k
4
REG3 7805
IN
470 F
100nF
OUT
3
+5V (FOR SFX & AUDIO)
GND
100nF
2
1000 F
18
17
16
MODIFICATIONS FOR THE MG959 ARM SERVO (ONLY)
x
Locate 50k pot within the servo
body. Unsolder (or cut) two outer
x
wires as shown here (red x).
2.7k
Solder in two 2.7k 1/4W (or 1/8W)
resistors in series between the wires
removed and the outer pot terminals
15
13
USELESS BOX
RB0
RA4
RB1
RA3
RB2
IC1
PIC1 6F8 8
PIC16F88
RA1
RB3
RA0
RB4
OSC1
RB6
OSC2
RA2
RB5
RB7
CTRL
6
CTRL
ARM
SERVO
7
LID
SERVO
MOUTH
SERVO
ARM SERVO: TURNIGY MG959
(MODIFIED – SEE BELOW LEFT)
LID SERVO: TURNIGY MG959
MOUTH: HOBBY TECH YM2763
8
9
FROG SOUND 3
10
FROG SOUND 2
12
FROG SOUND 1
1
MOUTH INHIBIT
D3-5
1N4148
11
680
A
10k
BOX
ILLUMINATION
K LED1
2.7k
+5V
1N5405
K
K
K
A
E
7805
GND
B
A
A
LP2950
BC547
LEDS
C
IN
OUT
GND
IN
GND
OUT
Fig.1: it’s essentially a project in two halves – IC1, 2 and 3 provide the servo control and trigger the voice unit, which is
the Digital Sound Effects Generator from August 2018. This has an inbuilt audio amplifier to drive a speaker.
open the lid easily – they
have to operate the switch instead.When the box is closed,
the bracket hooks onto the end
of the servo arm which is later
used to open the lid.
Whether you want to go to this
extreme is entirely up to you – just
remember, kids are inquisitive and
will try to open the box if you
make it easy!
servos, which provide all
the movement in the UseOPEN/CLOSE
less Box.
BRACKET
WHITE
There is one servo to raise and
LED
lower the lid, while another moves
the frog’s arm to provide the switching action.
Both of these are Turnigy MG959 25kg/
LID
SERVO
cm units, purchased from Hobby King
but one, that controlling the arm, needs
FROG LIPS ATTACH TO
to be modified slightly (we’ll look at
SMALLER SERVO
this in a moment).
The component parts
The third servo is a smaller, less
There are three parts to the
powerful model which moves the
ARM
design :
frog’s mouth in time with the
FROG ARM ATTACHES
SERVO
TO LARGE SERVO
• the mechanical part, which
words.
provides the movement of
It is a Hobby Tech 13kg/cm
the frog and its arm AND
model and came from Jaycar, Cat
opens and closes the box;
YM-2763.
• the electrical part, which
If you have some spare servos
provides the timing for the
in your junk box, you might be
mechanical actions; and
able to press them into service but
• the sound part, which al- This internal photo shows how the frog body is conkeep in mind the 25kg/cm rating
lows the frog’s chirping nected to the lid but the arm is removed and attaches of the two larger types – the lid is
and voice to be both re- to one of the larger servos which turns the switch off. not heavy but does require some
The rear servo opens and closes the lid via the alumcorded and played.
force to open and close it. And
inium bracket (not connected in this photo). This also
Froggy’s “hand” must strike the
prevents
the
lid
being
opened
by
inquisitive
fingers!
The servos
Note also the white LED attached to the lid and its con- toggle switch with enough presThe major part of the me- cealed wiring. You could copy this directly, or perhaps sure to turn it off.
chanical side is the three come up with your own mechanical arrangement.
Ordinary “hobby” servos such
68
Silicon Chip
CTRL
0V
0V
0V
5
1N4148
SC
Vdd
RA5/MCLR
S1
+5V
+5V
+5V
“DO NOT
OPERATE”
14
Vss
THE MG959 LID SERVO IS NOT MODIFIED
20 1 8
470 F
100nF
Australia’s electronics magazine
siliconchip.com.au
+5V
10F
100nF
5
ENVELOPE DETECTOR
IC2: OPA2340 OR MCP6022
7
IC2b
6
A
10 F
4
100k
8.2k
4
8
2
VR1
10k
D2
1N4148
1
IC2a
3
7
GP2
1 F
MULTILAYER
CERAMIC
GP5
IC3
PIC12F675
MCLR/GP3
GP4
GP0
GP1
2
3
6
Vss
470k
1.8k
56nF
K
4.7k
8.2k
VR1: MOUTH
THRESHOLD
ADJUST
5
1
Vdd
100nF
8
100k
C
22k
Q1
BC547
10k
B
E
12k
PART SUPER DIGITAL SOUNDS EFFECTS GENERATOR
(SILICON CHIP AUGUST 2018)
+5V
REG4
MCP1700-3.3
Link LK2 is permanently
closed (the header can be
replaced with a wire link).
OUT
IN
1 F
+3.3V
MCP1700
1k
ICSP
Vin
Vout
1
3
MICRO-SD
CARD SOCKET
4
PGD
4
5
PGC
5
+3.3V
1 F
28
AVDD/VDD
1
2
1
2
3
4
5
6
7
8
26
SDO1 18
SCK1 17
SDI1 25
1 F
AN4/RB2
RB0/AN2/PGED1
VREF+/AN0/RA0
RB1/AN3/PGEC1
AN5/RB3
24
7x 1k
22
7
SW6
21
FROG SOUND 3
6
SW5
11
FROG SOUND 2
5
SW4
10
FROG SOUND 1
4
SW3
19
3
SW2
16
2
1
S1
siliconchip.com.au
CON4
6
SDO2
1
2
SCK2
2
7
CS2
3
3
MCLK
4
VA
SDATA
AOUTL
SW1
15
8
SCLK/DEM
IC2
CS4334
LRCK
AOUTR
MCLK
AGND
270k
5
6
9
10 F
RB 8/TDK
RB14/RB16/AN9
+5V
22k
RB13/AN8
1
5
RB11/D+
PGED3/RB5
RB 10/D–
8
3
IC1
PIC32MM0256GPM028-I/SS
SW7
8
7
23
CLK1/RA2
RB9/TD0
CON1
TRIGGERS
+5V
VUSB3V3
RB15/RP17
1 F
1 F
13
VDD
VREF–/AN0/RA1
CS1
CD
1 F
MCLR
CON3
S2
+5V
+5V
LK2
GND
GND
10 F
14
1 F
IN–
IN+
Vcc
IC3 Out+
IS31AP4991
BYPASS
Gnd
SDB
4
Out–
7
6
2
8
SPEAKER
RB4/RP10/SOSCI
RA3/RP4/CLKO
RC9/RP19
SOSCO/RP5/RA4
RB 7/TDI
VCAP
RB 6/PGEC 3
AVSS
27
VSS
8
12
20
330pF
47k
22k
A
10 F
LED1
100pF
K
Australia’s electronics magazine
December 2018 69
+
GND
470µF
+5V
OUT
GND
100µF
D3-D5
3
2
1
TERMINALS 6
No. Value
1 470kΩ
2 100kΩ
1 22kΩ
2 12kΩ
2 10kΩ
2 8.2kΩ
2 4.7kΩ
1 1.8kΩ
1 680Ω
2 2.7kΩ*
4-Band Code (1%)
yellow violet yellow brown
brown black yellow brown
red red orange brown
brown red orange brown
brown black orange brown
grey red red brown
yellow violet red brown
brown grey red brown
blue grey brown brown
red violet red brown
5-Band Code (1%)
yellow violet black orange brown
brown black black orange brown
red red black red brown
brown red black red brown
brown black black red brown
grey red black brown brown
yellow violet black brown brown
brown grey black brown brown
blue grey black black brown
red violet black brown brown
Resistors for the Sound Card are all SMD – refer to the article in August/September.
Silicon Chip
5
diode and the resultant DC voltage
charges a 1µF capacitor.
The time constant of this capacitor and the parallel 100k resistor is
set so that the voltage applied to the
negative input of the second OPA2340
(IC2a) follows the envelope of the audio signal.
IC2a is wired as an inverting
Schmitt trigger whose output will be
low if the voltage on its negative input exceeds the voltage on its positive input.
If the mouth inhibit signal is high,
ie, BC547 transistor (Q1) is on, then
the voltage on the positive input is set
by the 10k potentiometer.
PIC12F675(IC3) operates the mouth
servo, opening the mouth if its input is
low and shutting it if its input is high.
In other words, if the envelope voltage
is high then the mouth is open and if
it is low the mouth is closed.
* required for modifying one servo for 180° operation. Preferably 1/8W; 1/4W should fit
70
CON3
A
K
LED2
4.7kΩ
8.2kΩ
8.2kΩ
100nF
AUDIO
IN
470kΩ
10kΩ
+
10µF
100nF
100kΩ
4148
D2
IC2
MCP6022
56nF
10µF
NP
100kΩ
10kΩ
© 2018 USELESS BOX
08111181 RevA
3x 1N4148 etc
4 ON CON4*
TO SPEAKER OUT
(PIN 2, CON2)*
Fig.2: the control PCB component overlay, which matches the photo at right.
Power for the Sound Effects/Audio amplifier board is taken from the pair of
terminals indicated, with other connections to that board shown in red. Other
connections were provided “just in case”!
Resistor Colour Codes (Controller only)
CON4
SOUNDS
S1
* CONNECTIONS IN RED ARE TO
THE DIGITAL SOUND EFFECTS PCB
(SILICON CHIP AUGUST 2018)
Q1
BC547
100nF
CON5
CON6
CON2
10kΩ
1000µF
+
1µF
IC3
VR1
IC1
PIC16F88-I/P
LP2950-5.0
680Ω
GND
12kΩ
+
REG3
7805
+100nF x 2
LID
MOUTH
PIC12F675-I/P
1.8kΩ
+
100nF x 2
11.4V
OUT
ARM
470µF
22kΩ
GND
REG1
7805
D1
4.7kΩ
+12V CON1
IN
REG2
+5V TO
SOUND
CARD
CARD*
+
5404
12V DC IN
FROM
INPUT
SOCKET
+
4148
The frog’s mouth moves in concert
with the audio. The mouth itself is
made from two half circles of brass
wire. One is fixed in the horizontal
plane adjacent to the servo shaft and
the other is connected to the servo
shaft itself.
To move the frog’s mouth in sequence with him (her? it?) speaking,
the audio signal is envelope-detected then this voltage is applied to a
Schmitt trigger so that we get a mouth
open/mouth closed signal to operate
the mouth servo pretty much in time
with the voice.
The first stage of the OPA2340
(IC2b) is wired as a non-inverting audio amplifier with a voltage gain of
11. Its output is rectified by a 1N4148
SERVOS
4148
Did someone mention mouth?
5V C 0V 5V C 0V 5V C 0V
100µF
+
4148
as those used for model aircraft, etc
will probably not have enough force
to achieve this.
The mouth movement is not quite
as difficult, so a typical model servo
should be quite adequate.
OK, back to the arm servo. As supplied, like most servos it only operates
through 90° but we need it to operate
through 180°.
The easiest way to achieve this is
to open up the servo (it’s not difficult) and locate the two ends of the
5k position potentiometer. Disconnect the wires from each end of the
pot and add in a 2.7k, 1/4W resistor (or even 1/8W if you can get them)
in series with the wire ends and the
pot terminals.
Close the servo back up again and
it will now work through 180°.
There’s a YouTube video which
shows how to do this if the description isn’t clear: http://youtu.be/F0k9CklRE0
Australia’s electronics magazine
The 10k potentiometer provides
an adjustment so that the mouth
moves in time with the audio.
The voice recorder/amplifier
When Les Kerr originally submitted
this project to SILICON CHIP, he used
the Voice Recorder published back
in our December 2007 for the sound
effects, along with a separate “Champion” audio amplifier.
There was a major problem with
this: the HK828 chip is now obsolete and becoming very hard to get
(it’s even been discontinued by Jaycar Electronics, who developed that
project).
So we revised the Useless Box using the Super Digital Sound Effects
Module we published just last August/September.
This will ensure that it will be current for many years.
It reads its messages from an SD
card and uses a PIC micro to select
them and the appropriate message
to send to its inbuilt audio amplifier.
There’s another reason to use the
August module: the separate audio amplifier in the original Useless Box is no longer required – the
IS31AP4991 can provide up to 1.2W
into an 8-ohm speaker.
All you need to do with the new
sound effects module is connect a
speaker – and this can be just about
anything that will fit in the box.
Chances are you have a suitable
speaker in your junk box!
You can record whatever messages
siliconchip.com.au
Here’s a photo of the control PCB at left, reproduced same size.
Many readers will be delighted to know that it’s all “through hole”
components – no 40/20 vision required for this one! No photo nor
overlay is shown for the Sound Effects board: see August 2018 issue.
Note that some servos will have different pinouts and will need to be
modified to suit.
in whatever voices you want – the
August/September 2018 tell you how
to do that.
If you need an authentic frog sound,
you’ll find a recording of the Per tree
frog at www.anbg.gov.au/sounds/
Software
Each of the three PIC microcontrollers in the Useless Box require different firmware.
If you purchase the PICs from
SILICON CHIP they will come preprogrammed; otherwise you will
need to download the hex files from
siliconchip.com.au and program them
yourself. We’re assuming that you
have the necessary knowledge and
equipment to do this!
You will need 0811118A.hex for
the PIC16F88-I/P and 0811118B.
hex for the PIC12F675-I/P. The firmware for the Sound Effects Module
pic (PIC32MM0256GPM028-I/SS) is
0110718A.
So what does it do?
Not much . . . it’s pretty useless!
We’ve covered a lot of this earlier in
the description of the various sections
but in a nutshell, the Useless Box IC1
(PIC16F88) lies dormant, waiting for
an input from S1, the “Do Not Operate” switch on the RB0 input (pin 6).
This input is normally held low by a
10kresistor to 0V but goes high (ie,
to 5V) when the switch is operated.
This switch operates “upside
down” to what you might expect –
“up” is on and “down” is off.
This is so Froggy’s hand can turn
the switch back to “off” by pressing
down on it. (It’s a lot harder to go the
other way!). The miscreant who disobeys the warning sign pushes it up
to operate it.
Each time the switch is turned on
there is a different reaction.
The first time, it does not play any
sounds – the frog switches S1 off in
silence.
The second time, it drives RB4 high
(pin 10 – frog sound 2; “Go away!”)
and the next time, RB3 (pin 9 – frog
sound 3; “I told you to go away!”),
which in turn trigger the Sound Effects Module IC1 inputs on CON4.
First is pin 19; (RC9/RCP19), then
pin 10, RB4; and finally pin 11 (RB4).
At the same time (and in the same
sequence) the RB1 and RB2 outputs
(pins 7 and 8) send the appropriate
signals to their respective servos –
RB1 activates the arm servo and RB2
activates the lid servo.
The mouth servo operates slightly
differently as it has to work (roughly!)
in time with Froggy’s voice.
We won’t try to reinvent wheels by
describing the Sound Effects Module
here – if you want to fully understand
how it operates (including how you
record your voice messages on the SD
card), please refer to the articles in August and September 2018 (siliconchip.
com.au/Series/325).
Of course, the three “frog sound”
messages can be anything you wish
to record on the SD card.
Power Supply
The Useless Box is powered from
a 12V DC, 1A plug pack, connected
to the box via a suitable DC socket .
Power connects from this socket
to the +12V in and GND terminals at
the top left of the PCB, thence via a
1N5404 reverse-polarity protection
diode.
At 3A, this diode is arguably higher rated than might appear necessary
but a typical 1N4xxx diode (rated at
ROUTINES
There are three different routines of operation that follow each other. They are started when the toggle switch on the front of the box
is operated.
The first:
1 Inhibit mouth movement
2 Chirping sound (1) off
3 Open the box lid
4 Switch the light on
5 Frog arm moves out, closing the switch
6 Arm retracts
7 Switch light off
8 Box lid closed
siliconchip.com.au
The second:
1 Start frog sound 2 “go away”
2 Enable frog mouth movement
3 Open the box lid
4 Switch the light on
5 Frog arm moves out closing the switch
6 Move frog arm back a few degrees
7 Mute off
8 Pause 1.8 seconds to allow time for frog’s
voice to play
9 Retract frog arm
10 Switch off light
11 Close box lid
Australia’s electronics magazine
The third:
1 Open and close box lid twice.
Switch light on when lid is open and
off when closed. Open lid
2 Switch the light on
3 Start frog sound 3
4 Frog arm moves out, closing the switch
5 Move frog’s arm back a few degrees
6 Pause 2.5 seconds to allow time for
frog’s voice to play
7 Retract frog’s arm
8 Close lid
9 Switch initial frog chirping sound on (1)
December 2018 71
1A maximum) may not have sufficient margin for error, particularly
when more than one servo is operating. So a 3A diode it is. They’re not
that much more expensive than lower-rated diodes.
You will note on the circuit diagram
that there are actually three 5V power
supplies – one to power the servos,
one to power the control microprocessor and other ICs and one to power the
audio amplifier. The latter is further
reduced to 3.3V for the SFX module.
It might appear that having three
separate 5V supplies is a bit wasteful.
But it was done to avoid any power supply noise/feedback caused by
the servos operating (they can be
fairly noisy electrically!) and affecting the microprocessor circuits and/
or the audio.
Besides, 5V regulators are quite
cheap!
Construction
Once again, there are two parts to
the project: the control PCB along
with its hardware and the sound PCB,
most of which is mounted on a second board.
For detail of the sound PCB, refer
to the articles in the August and September 2018 issues (siliconchip.com.
au/Series/325).
Most of the construction techniques can be seen from our photographs. While this seemed a sensible
approach, no doubt there are many
others!
We’ve already mentioned the servos
and their functions. The rest is basically the electronics assembly, which
is quite straightforward, and the dressing of the project.
The frog itself
We originally purchased a toy frog
from a $2 shop but found it too difficult to modify. So instead we made
one.
(OK, I lie: Mrs Kerr made one – she’s
much more adept at the sewing machine than I!).
The photos give a good idea of our
Froggy – it’s basically a tube of soft
green stretch cloth for the body (he
needs to be quite flexible when lifted
up and down) and a completely separate arm, stiffened by some heavy wire
attached to the servo.
This arm needs to be quite stiff in
order to stay in place and also positively hit that switch. You don’t really
72
Silicon Chip
Parts list – Useless Box
1 hinged “jewellery” box, size approximately 200mm x 150mm x 110mm (see text)
Control Board
1 double-sided PCB, 96 x 67mm, code 08111181 (from siliconchip.com.au/shop)
1 fabric toy frog (see text)
1 SPDT toggle switch (S1)
2 large servos, ~25kg/cm [eg Turnigy MG959 (Hobby King)]
1 small servo, ~13kg/cm [eg Hobby Tech (Jaycar) YM-2763]
7 2-way PCB mounting terminal blocks
1 3-way PCB mounting terminal blocks
3 3-pin male polarised headers for servos
1 TO-220 mini heatsink [Jaycar HH8502] with M3 6mm screw and nut
1 chassis-mounting DC socket
Aluminium brackets (see text)
Stiff wire (for mouth - see text)
Semiconductors
1 PIC16F88-I/P, programmed with 0811118A.hex (IC1)
1 PIC12F675-I/P, programmed with 0811118B.hex (IC3)
1 OPA2340 or MCP6022 rail-to-rail CMOS op amp (IC2)
2 7805 5V 1A positive voltage regulators (REG1, REG3)
1 LP2950-5.0 5V positive voltage regulator (REG2)
1 BC547 NPN transistor (Q1)
1 1N5404 3A power diode (D1)
4 1N4148 signal diode (D2-D5)
1 5mm high brightness white LED (LED1)
NOTE: Where there
is a clash of part nos
between the control
board and the sound
board (eg, LED1, IC1,
etc), each refers to
the part no on its respective PCB.
Capacitors
1 1000µF 16V electrolytic
2 470µF 16V electrolytc
2 100µF 16V electrolytic
1 10µF 16V electrolytic
1 10µF 16V NP electrolytic
1 1µF 16V electrolytic
1 1µF 16V multi-layer ceramic
6 100nF MKT or ceramic
1 56nF MKT
Resistors (all 1/4W, 1% unless stated otherwise)
1 470k 2 100k
1 22k
2 12k
2 8.2k
2 4.7k
1 1.8k
1 680
1 10k mini horizontal trimpot (VR1)
2 10k
2 2.7k 1/8W if possible
Sound Board*
(Note: component IDs are from original August 2018 project)
1 double-sided PCB, coded 01107181, 55 x 23.5mm
1 SMD microSD card socket (CON1) [Altronics P5717 or similar]
2 mini SMD two-pin tactile pushbutton switches (S1,S2) (optional)
[eg, Switchtech 1107G]
1 5-pin header (CON3) (optional, to program IC1)
1 speaker, size to suit (8 or greater)
Semiconductors
1 PIC32MM0256GPM028-I/SS programmed with 0110718A.hex, SSOP-28 (IC1)
1 CS4334 16-bit stereo DAC, SOIC-8 (IC2)
* The Sound Board is avail1 IS31AP4991 mono bridged audio amplifier, SOIC-8 (IC3) able as a complete kit (Super Digital SFX Module),
1 MCP1700-3.3 LDO linear regulator, SOT-23 (REG1)
containing all parts listed
1 blue SMD LED, 3216/1206 package (LED1)
Capacitors (all SMD X7R ceramic, 6V, 2012/0805 size)
3 10µF
7 1µF 16V 1 330pF
1 100pF
Resistors (all SMD 1%, 2012/0805 size)
1 270k 1 47k
2 22k 8 1k
1 0 (LK2)
here, including pre-programmed IC1 and PCB, but
NOT the speaker) from the
SILICON CHIP online shop –
see www.siliconchip.com.
au/shop/20/4658 for more
details).
SC
Australia’s electronics magazine
siliconchip.com.au
notice that Froggy only has one arm and that it’s not actually attached to the body!
Froggy has a separately-made head, made from the same
material as the body but is filled with cotton wool to help
it keep its shape.
The red mouth is sewn in and it holds its shape with
two wires. One of these is fixed but the other attaches to
the mouth servo so he talks in time with the voice.
A pinched nose (“nostrils” sewn together) and a pair of
black button eyes fastened through some white discs finish off the design.
You’d have to agree that Froggy looks quite . . . froggy!
By the way, if you (or the grandkids!) have an aversion to
frogs, there are obviously many other cloth toys out there
that could be used, or made. Just follow the same principles.
Finally, we needed to ensure that the lid stayed closed
when the lid servo was not being actuated – and couldn’t
be simply lifted up “for a look”!
So we made a small bracket to attach the lid to the servo
arm to ensure it worked as we wanted it to. Again, this
can be clearly seen in the photos.
Mounting the PCBs
Basically, it’s just a matter of choosing a location which
doesn’t interfere with any of the mechanical “works” –
the servos which open the lid, operate Froggy’s arm and
his mouth.
You can get some idea of the way we did it from the
photos. Your method may of needs differ depending on
any “extras” inside your case – such as a jewel drawer,
for instance.
We’ll leave that entirely up to you but a bit of experimenting might be needed to find the right positions.
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Connecting the PCBs
Simply follow the labels on the PCB connectors – they’re
quite self-explanatory with one exception:
There are two “+5V OUT” terminals (with associated
grounds). To avoid any interference between the servos
and ICs/audio module, use the upper pair of +5V and
GND terminals for the 5V supply to the sound effects PCB.
You can ignore the lower 5V and GND terminals along
with the 11.4V and its GND terminals – they was provided
“just in case” they were needed.
There are four other connections to be made between
the control board and the Sound Effects board – the “audio in” which feeds the mouth movement circuitry (envelope detector and servo control), along with three diodes.
The former is self-explanatory – it is just a suitable length
of hookup wire linking the two boards.
With any luck, (depending how you mount the two
boards) the three diodes can make the connections between the two – otherwise short lengths of hookup wire
may be required as well.
LED2 on the control board is an ultra-bright white type
(the brighter the better). We found this one diode was
enough to illuminate the internals when Froggy did his
thing.
It can be attached to the inside of the lid with glue and
the wires hidden in a hole drilled through the case lid.
Just remember to leave plenty of slack in the connecting
wires (to CON4) to allow the lid to open and close. Light
gauge wire should be used so it can easily flex.
SC
siliconchip.com.au
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Australia’s electronics magazine
December 2018 73
Using Cheap Asian Electronic Modules Part 21: by Jim Rowe
A stamp sized
digital audio player
The DFPlayer Mini is a low-cost digital audio player module. It's
available from popular internet suppliers, including Banggood, as well
as from marketplaces like eBay and AliExpress, for as low as a few
dollars, including postage. Despite its size and price, it can do a lot!
This is a very flexible module with
a great many features. I was very impressed after trying the module out
for myself.
One of the best things about it is
that it plays several different audio
file formats, including MP3, WMA
and WAV, in mono or stereo, and it can
read those files off either a microSD
card or USB flash drive with a capacity up to 32GB in either case. But it
has a lot of other features, so let's take
a look at the hardware involved and
how to drive it.
What's inside the module
Circuit diagrams for the DFPlayer
Mini module are hard to find but an
examination of the module reveals that
it's based on two ICs: a YX5200-24SS
(IC1) which does most of the work
and a smaller 8002 audio amplifier
chip (IC2).
While data sheets for both devices
are available, the sheet for the YX5200-
24SS is almost entirely in Chinese. But
I was able to glean enough info to draw
the module's internal block diagram,
shown in Fig.1.
The YX-5200 chip is the module's
brains. Inside it, there's a 16-bit MCU
(micrcontroller), an analog DSP (digital signal processor), EPROM and flash
memory, a 24-bit stereo DAC (digitalto-analog converter), a serial UART
for communication with an external
MCU and ports to communicate with
a microSD card or a USB thumb drive.
All this in a compact 24-pin SSOP
(SMD) package – it's virtually a complete digital audio system on a chip!
The YX-5200 chip can play back
MP3, WMA and WAV files at sampling rates of 8kHz, 11.025kHz, 12kHz,
16kHz, 22.05kHz, 24kHz, 32kHz,
44.1kHz or 48kHz.
It can handle files on either microSD (“TransFlash” or TF) cards or
USB thumb drives with capacities up
to 32GB, formatted with a FAT16 or
FAT32 file system.
You can store up to 45 hours of
CD-quality WAV files on a 32GB
card/drive, or about 23 days worth of
128kbit MP3 files.
The 24-bit stereo DAC in the YX5200 is claimed to provide a dynamic
range of 90dB, with a signal-to-noise
ratio (SNR) of 85dB. That isn't exactly
hifi but it isn't too bad either.
The built-in MCU and DSP combine
to provide features like audio gain adjustment over 31 levels and the ability to select one of six playback tonal
equalisation settings.
You can also select the playback
mode (normal/repeat/folder repeat/
single repeat/random) and the playback source (USB drive, microSD card
or a couple of other options).
It also provides a BUSY logic output signal which is at logic low level
(<800mV) when playing a file, rising
to logic high (~3.5V) when playback
stops.
Turning to IC2, its operation is
quite straightforward. Housed in an
8-pin SOIC package, it's basically just
a low-power audio amplifier with a
few extras.
Running from 5V, it can deliver
up to 2W into a 4W loudspeaker load
with 10% total harmonic distortion
(THD+N), or 1.5W into an 8W load
with 1% THD+N.
Views of the top (left) and bottom of
the DFPlayer Mini module with a
microSD card inserted. It is shown at
close to double life size for clarity.
74
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
Features & Specifications
R Just 21 x 21 x 12mm including microSD card socket and pin headers
R Plays MP3, WMA and WAV audio files (4.3 filenames)
R 24-bit stereo DAC
R Built-in 2W mono bridge-mode amplifier
R Plays files from microSD cards or USB flash drives (up to 32GB)
R Multiple control options, from as few as four pushbutton switches
to full serial mode control from a microcontroller such as an Arduino
or Micromite
R Line-level stereo outputs which can also drive headphones
R Six playback equalisation options: Normal (flat), Pop, Rock, Jazz,
Classical and Bass
R Programmable playback volume in 31 steps (0-30)
R Runs from a 3.3-5.2V supply, drawing 25mA when idle or 200250mA during playback
It provides a push-pull (bridged)
output and no output coupling capacitors, snubber network or bootstrap capacitors are needed. It's also
unity-gain stable, has an externally
programmable gain and includes circuitry to suppress clicks and plops
during power on/off.
As you can see from Fig.1, the DFPlayer Mini module makes good use
of the many features provided by
both ICs.
As well as providing all of the main
control inputs needed by IC1, it also
features a microSD card socket on the
top of the module connected directly
to IC1. The latter's BUSY signal output
is brought out to a pin and also drives
LED1, a tiny blue SMD LED.
The left and right channel outputs from the YX5200's DAC are also
brought out for use in driving either
headphones or an external amplifier,
in addition to being mixed together
and fed into IC2 to drive a speaker
directly.
No socket is provided for plugging
in a USB thumb drive – just a couple
of pins identified as USB- and USB+.
I couldn't find any information on the
use of these pins anywhere in the commonly available data sheets for the DFPlayer Mini module but I guessed that
these could be connected to the D- and
D+ signal lines of a USB socket, and as
you will see later, I was right.
Fig.1: block diagram of the DFPlayer
Mini audio player module.
The total current requirement is
around 25mA when idle, rising to
around 200-250mA during playback.
The module can be used as a selfcontained audio player controlled
merely using four SPST pushbutton
switches, connected as shown in Fig.3.
Alternatively, a much larger array of
20 pushbuttons can be connected as
shown in Fig.4.
Otherwise, its operation can be controlled entirely from an Arduino, a Micromite or many other kinds of microcontroller, using the UART serial port
lines at pins 2 (RX) and 3 (TX), along
with the BUSY signal from pin 16. This
configuration is shown in Figs.5 & 6.
The rest of the connections are to
make use of the module's extra features.
For example, you can use it to play
files from a USB thumb drive by connecting up a Type A USB socket as
shown at the top right of Fig.2, with
pin 1 connected to the +5V supply,
pins 2 and 3 to pins 15 (USB-) and 14
(USB+) of the module, and pin 4 to the
module ground (pins 7 or 10).
The dashed connections to pins 4
(DAC_R) and 5 (DAC_L) of the module show how it can be used to drive
either stereo headphones or line-level
outputs to an external stereo amplifier
or hifi system.
Returning now to Fig.3, which
shows the simple four-pushbutton
control scheme, S1 and S2 have dual
functions in this mode. A short press
is used to move to the previous track
(S1) or the next track (S2), while a
longer press either decreases (S1) or
increases (S2) the volume. S3 and S4
each have only single functions, to
start playing the first track (S3), or the
fifth track (S4).
The more complex pushbutton con-
Putting it to use
Fig.2 shows how to wire up the
DFPlayer Mini module. The speaker
(if used) connects directly between
the SPK_1 and SPK_2 pins (6 and 8)
while the module's power supply (3.35.2V DC) is fed to pin 1 (Vcc) and pins
7/10 (GND).
siliconchip.com.au
Fig.2: This shows how to connect the audio player module for playback to a
speaker, headphones or other audio devices via the level outputs.
Australia’s electronics magazine
December 2018 75
Press S1: previous track
Hold S1: increase volume
Press S2: next track
Hold S2: decrease volume
Press S3: play first track
Press S4: play fifth track
Fig.3: the simplest method of controlling the DFPlayer module is by using four
pushbutton switches. Track 5 is equivalent to 005.mp3 (four characters at most
for a filename, three for the extension); folders are named 01 to 99.
trol arrangement of Fig.4 is a bit more
tricky. To allow twenty pushbuttons
to be connected using just two pins,
each of the ten pushbuttons in a given
“bank” has a different resistor value
connected in series.
The chip then measures the current
sunk from pin 12 or 13 when a button is pressed and depending on what
range it is in, it knows which button
was pressed.
In this mode, most of the extra
switches (S7 - S20) are simply used to
allow direct selection of tracks to play.
Switches S5 and S6 basically duplicate the actions of S1 and S2 in Fig.3,
while the first four switches (S1 - S4)
allow control over the playback mode
(single track/continuous), playback
source (USB/SD/SPI/SLEEP), enable
loop all mode and provide the pause/
play function.
Controlling it with a micro
Hooking the DFPlayer Mini up to a
microcontroller is simple, thanks to the
module's built-in UART serial port. You
just need to connect the module's RX
input (pin 2) to the serial TX output of
the micro and connect the module's TX
output (pin 3) to the serial RX input of
the micro. The GND of the module (pin
7 and/or 10) also needs to be connected
to the micro's ground network.
The module's UART is pre-programmed to communicate at 9600
baud, with the basic 8N1 protocol. It's
also a good idea to link the module's
BUSY output (pin 16) to a digital input on the micro so that the control
program can tell whether the module
is playing a file or has stopped.
Arduino specifics
Fig.5 shows the connections for controlling the module from an Arduino.
It's powered from the Arduino's 5V
supply, which is fed to its Vcc pin (pin
1). For serial communications, we're
using Arduino digital I/O pins 10 and
11, which are driven by the SoftwareSerial library code.
The D11 digital output is connected to the RX pin on the module via
a 1kW series resistor. That's because
the module inputs can handle a 3.3V
signal while the Arduino pins have a
5V swing.
The resistor limits the current into
the module's RX pin to a reasonable
level (less than 2mA) when D11 is
driven high. The only other connection needed is between pin 16 of the
module (BUSY) and D3 of the Arduino, for the reasons described above.
For clarity, Fig.5 does not show a
USB socket, headphone socket, line
outputs etc, which were shown in
Fig.2. But these can certainly be included if you need those functions.
There are many different libraries
and sketches on the internet which
show how to drive the DFPlayer Mini
from an Arduino, although some are a
bit flakey and/or hard to understand.
But one of the best is from the manufacturers themselves, DFRobot and
is called “DFRobotDFPlayerMini1.0.3.zip”. It includes a set of exam-
Fig.4: a more complex method for control involves 20
pushbuttons, each with a series resistor (except S10 &
S20). S7-20 just allows playback of tracks 1-14 directly
(holding the switch will cause it to repeat indefinitely),
while the rest of the switches are for playback
functionality with S5/6 identical to S1/2 in Fig,3.
Switch functions:
S1 – single track/continuous playback
S2 – change playback source (USB/SD/SPI/sleep [none])
S3 – loops the current track
S4 – pause/play
76
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
Fig.5: wiring diagram for
the audio player module
when connected
to an Arduino.
ple sketches and you will find a link
to download it below.
Driving it from a Micromite
If you're one of the many Micromite enthusiasts, Fig.6 shows the basic connections needed to control the
DFPlayer Mini module from a Micromite Backpack.
The arrangement is very similar to
that for the Arduino. The module's
RX (2) and TX (3) pins are connected to pins 9 and 10 of the Micromite
respectively, again with a 1kW series
resistor in series with the line to the
module's RX pin.
Pins 9 and 10 of the Micromite are
the TX and RX pins for the Micromite's
COM2 serial port. The remaining connection is from the BUSY pin (16) of
the module to pin 24 of the Micromite, again to provide a playing/not
playing signal. And again, for clarity,
Fig.6 leaves out any extra connections
you may wish to make to the DFPlayer module, like those shown in Fig.2.
I couldn't find any pre-existing Micromite programs to control a DFPlayer Mini, so I wrote one myself,
after studying the YX5200-24SS data
sheet and also some of the Arduino
library files. The program is called
“DFPlayerMini control program.bas”
and it's available from the Silicon
Chip website.
It's designed to run on the LCD BackPack (see February 2016 [siliconchip.
com.au/Article/9812] and May 2017
[siliconchip.com.au/Article/10652]
issues);
As you can see from the screen grab
of the LCD touchscreen, the program
gives you a set of six touch buttons
labelled PLAY, PAUSE, PREV, NEXT,
VOLUME (down) and VOLUME (up).
Touching any of these buttons makes
the Micromite send a command to
the module to achieve the desired response, similarly to how the hardware
switches shown in Fig.3 work.
Now this MMBasic program is pretty
simple but it should give you a good
starting place for writing more elaborate programs yourself. With the technical information on the DFPlayer
Mini module in this article, you should
be able to get the module performing
all kinds of impressive tricks!
Handy links
Module information and software:
siliconchip.com.au/link/aald
Software library and sketches:
siliconchip.com.au/link/aale
Documentation and Arduino library:
siliconchip.com.au/link/aalf
SC
Above: screenshot of the MMBasic example program running on a Micromite.
Fig.6 (right): wiring diagram of the audio player module connected to a Micromite.
siliconchip.com.au
Australia’s electronics magazine
December 2018 77
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.
Simple guitar practice amp
When you are playing an electric
instrument at home, you don’t need a
big, powerful amplifier. A few watts
is plenty, especially with an efficient
speaker. For example, the Dipole Guitar/PA Speaker described in the September 2018 issue (siliconchip.com.
au/Article/11223) produces around
100dB <at> 1W/1m, which is quite loud.
This circuit is a very simple amplifier with a high input impedance, to
suit magnetic or piezo pickups. The
high input impedance is provided by
a JFET input stage. This also introduces some second harmonic distortion, which affects the tone produced
by the speaker.
Since the circuit runs off a 9-15V DC
supply, you can use a wide variety of
power supplies, including standard
plugpacks and lead-acid or lithiumion batteries.
The signal from the instrument
pickup is applied to CON1, where a
10MW resistor to ground provides DC
biasing. The signal is then AC-coupled
to the gate of JFET Q1 by a 10nF capacitor with a 1kW series resistor to protect
78
Silicon Chip
the circuit from spikes. The JFET gate
is also biased with a 10MW resistor to
ground, setting the input impedance
to around 5MW (10MW || 10MW).
Q1 acts as a source-follower buffer, with a gain slightly less than unity. Its drain supply voltage is filtered
by a 100W series resistor and 100µF
& 100nF bypass capacitors, to keep
supply ripple out of the audio signal.
The buffered signal at its source has
a DC level around half supply, due
to the voltage developed across the
1kW source resistor from the standing current through Q1. But this current depends on the exact JFET used
and since it and the supply voltage
can vary, it may not sit exactly at half
supply. That isn’t a problem though,
as the output stage will overload before the input buffer.
The buffered signal is fed to a preout at CON2, which could be used for
level monitoring or to connect an external amplifier. It’s coupled to CON2
via a 10µF non-polarised capacitor so
that the DC bias can be set to ground
by the 100kW resistor.
Australia’s electronics magazine
The signal is also fed to power amplifier IC1 via a 2.2µF non-polarised
capacitor. This is a “power op amp”
with internal feedback to provide a
fixed gain of 177 times (47dB). That
high gain is needed since typical electric instruments only produce a few
tens of millivolts and we need to increase that to a couple of volts to drive
the loudspeaker.
IC1 can drive a 4W load at up to 5W
with a 13.2V supply, or 6W with a 14.4V
supply. It can also drive an 8W load
but the output power will be less; in
this case, you would ideally use a 15V
supply to obtain the maximum possible power. It will need a heatsink with
a thermal resistance to ambient of less
than 10°C/W. Its quiescent power is
1-2W, depending on the supply voltage.
IC1 will shut down if it overheats,
to protect itself. It also has overload/
short-circuit protection and circuitry
to reduce clicks and thumps from the
speaker at power-on and power-off.
1000µF & 100nF bypass capacitors
are provided for IC1, to keep its supply
impedance low. It drives the speaker
via a 2200µF electrolytic capacitor, to
remove the DC bias at its output. This
siliconchip.com.au
Circuit
Ideas
Wanted
Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your
PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online
Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au
Accurately measuring voltage and current at the same time
If you are trying to measure the voltage across a device and the current
flow through it at the same time, the
resulting readings can be inaccurate,
especially if one or both of the readings are low values.
That's because ammeters have
a non-zero resistance and voltmeters have a finite resistance.
So when you place an ammeter
in series with a circuit, there is
a voltage drop across it (the meter's “burden voltage”).
This is generally higher at lower
current ranges. If the voltmeter is connected to point “A”, that voltage drop
will mean that it does not read the actual voltage across the load.
And when you connect a voltmeter
across a circuit, some current will flow
through it, potentially affecting your
current reading (the meter's “burden
current”). This will be the case when
the voltmeter is connected to point
“B”. So regardless of which way you
will introduce some distortion but given the relatively low power levels and
the fact that this is a practice amp, that
doesn’t matter. IC1’s rated distortion
is around 0.1%.
The voltage at the speaker is divided
down by a factor of 11 by two resistors,
to provide a headphone output. Ideally, the headphone impedance should
be at least 32W or else the frequency
response may be less than ideal due to
the relatively high driving impedance.
Power switch S1 is for convenience
and the supply current flows through
2A fuse F1 to protect the supply from
circuit faults. Diode D1 will cause F1
to blow if the supply polarity is connected incorrectly. LED1 lights to indicate that the circuit is powered.
A volume control can be added by
replacing the 1kW resistor connected
to the source of Q1 with a potentiometer whose wiper is fed to pin 1 of IC1
via the 2.2µF capacitor.
Petre Petrov,
Sofia, Bulgaria. ($60)
siliconchip.com.au
connect it, your measurements will
be inaccurate.
For example, a voltmeter with a
200V range will typically have a resistance of around 10MW and that translates to a burden current of up to 20µA.
An ammeter with a 20µA range may
have a resistance of 1kW and therefore
a burden voltage of up to 20mV.
Ammeter burden voltages were discussed in detail in an article on building a Microcurrent DMM Adaptor in
the April 2009 issue (siliconchip.com.
au/Article/1400).
Determining error magnitude
It is relatively easy to compensate
for these errors. You need to measure
the resistance of your voltmeter and
ammeter (on the ranges you will be using) and then plug these into some formulae, along with the readings, to calculate accurately compensated values.
You could do this by simply connect an ohmmeter across each set of
meter terminals (when set in the correct mode) and make a note of the resistance reading.
However, ohmmeter accuracy is not
normally that good (typically around
0.5-1%) so instead, I recommend you
purchase two 0.1% resistors, close in
value to the resistances of your two
Australia’s electronics magazine
meters (either based on the manual/
datasheet or a rough measurement).
Note that the highest value 0.1%
resistor you're likely to find at a reasonable price is 1MW but that will
be adequate for measuring
the resistance of a nominally 10MW meter. You can get
0.1% resistors from suppliers like element14, Digi-Key
and Mouser.
Now connect one of the
resistors in series with the meter
and apply a stable voltage (eg, from
a DC bench supply), then measure
the voltage across the known value
resistor and the meter terminals. The
voltages will be proportional to the
resistances.
For example, if you connect a 1MW
0.1% resistor in series with a voltmeter and get a reading of 0.36V across
the resistor and 3.72V across the meter, you can then determine that the
voltmeter's burden resistance is close
to 1MW × 3.72V ÷ 0.36V = 10.333MW.
Calculating the true values
Once you know the meter resistances and which reading you need to
correct, you can plug the values into
the correction formula.
In the case where you have the voltmeter across the supply, you need to
correct the voltage reading and the
formula is:
Vload = Vmeasured − Imeasured × Rammeter
In the case where you have the
voltmeter across the load, you need
to correct the current reading and the
formula is:
Itrue = Imeasured − Vmeasured × Rvoltmeter
As this correction is especially applicable when plotting voltage/current pairs to form a V-I curve, you can
build the appropriate formula into a
set of spreadsheet cells to automatically calculate the corrected values in
a third column.
Rodger Bean,
Watson, ACT. ($50)
December 2018 79
1kHz crystal-locked sinewave oscillator
Sometimes you need a clean sinewave with an accurate frequency for
testing certain equipment. This circuit
provides a 1kHz sinewave which will
not drift in frequency as its frequency
is locked by a crystal resonator.
It uses a Wien Bridge Oscillator to
generate the sinewave for minimum
distortion but it does not require a
small lamp for amplitude stabilisation
as many Wien Bridge circuits do. It
uses a JFET in this role instead.
Since you can't easily get a 1kHz
crystal, a 4.096MHz crystal (X1) is
used instead. This is driven by the
internal oscillator amplifier in IC2, a
4060B binary counter. 22pF load capacitors are connected from each end
of the crystal to ground to make the
circuit resonant. Most crystals require
load capacitors close to this value.
A 100W series resistor limits the
crystal drive power to a safe level
while a 10MW resistor across the crystal provides a bias current for the oscillator amplifier to make oscillator
start-up reliable.
IC2 has outputs labelled O3 through
O13 which produce square waves at
a fraction of the crystal frequency.
The frequency at O3 is divided by
80
Silicon Chip
16 (23+1), O4 is divided by 32 (24+1)
and so on, to O13 which is divided
by 16,384 (213+1). The one we want is
O11 which is divided by 4096, giving
precisely 1kHz.
This is fed straight to the “pulse out”
terminal but also passes through a series of three low-pass RC filters, each
of which has a -3dB point of just over
1kHz. These help to turn the square
wave output of IC2 into something
smoother and more like a sinewave.
They also attenuate the signal somewhat, as their corner frequency is close
to the signal frequency.
The signal then passes through a
high-pass filter with the same corner
frequency, to remove the DC bias and
provide some further attenuation. Attenuation is needed because we want
the reference signal just to nudge the
oscillator one way or the other to keep
it locked to the crystal; if the signal
from the crystal had too much influence on the oscillator, it would distort
the sinewave output.
That attenuated signal is coupled to
one side of the Wien Bridge oscillator
which is formed around op amp IC1a.
The main sections of the bridge are
symmetrical and each consist of a re-
Australia’s electronics magazine
sistance provided by three fixed and
one variable resistor plus a 33nF capacitor. One such network connects
between the non-inverting input (pin
3) of IC1a and ground, with the other
identical network between the pin 3
input and pin 1, the output.
Trimpots VR1 and VR2 are adjusted so that the oscillator's natural frequency is close to 1kHz, then the signal from the crystal, which is injected
to the top end of the 1kW resistor to
ground, makes the required adjustments.
IC1a needs to operate with a gain of
about three times to start oscillation,
which is provided by the 100kW and
47kW feedback resistors. But the gain
needs to fall until it is close to unity
once the oscillator starts, to avoid gross
distortion. JFET Q1 is configured to
acts as an automatic gain control, providing this function.
JFETs are depletion-mode devices
which means they conduct current
with no gate bias. This is an N-channel type, so its gate needs to be pulled
negative relative to its source to reduce the channel current. Note that
the drain and source are identical and
change roles depending on whichever
has a more negative voltage, but that
doesn’t affect the operation of the circuit, since the gate voltage is biased
negative.
Since op amp IC1 runs from a split
supply, which includes a negative rail,
a negative bias voltage can easily be
derived from the output of IC1a. Each
time output pin 1 swings negative,
diode D1 is forward-biased and this
charges the 1µF capacitor to a negative
voltage, which is reduced to a lower
voltage by trimpot VR3 and its wiper
is connected to the gate of Q1.
VR3 is adjusted so that once the
oscillator amplitude is at the desired
level, Q1 gets just enough bias voltage
to reduce the gain of IC1a to the point
where the amplitude stabilises. Thus,
VR3 controls the output amplitude.
Note that the current through VR3 continually discharges the 1µF capacitor,
so that its voltage is reduced if the oscillator amplitude falls.
The remaining three op amps within
the LF347 quad package provide some
extra functions. The sinewave output
from IC1a is buffered by IC1b before
being fed to the output terminal so that
any loading from the external circuit
siliconchip.com.au
will not affect the oscillator. IC1c is
configured as a comparator, to provide
a square wave output derived from the
sinewave, which should have a duty
cycle close to 50%.
IC1d compares the reference frequency from the crystal to the output
of the oscillator and drives LED1 and
LED2. These should not be illuminated if the two oscillators are locked
properly. If for some reason the sinewave oscillator is not at the correct
frequency (eg, VR1 or VR2 needs adjustment) then you will see LED1 and/
or LED2 flash.
Jumper JP1 is used as a power
switch, JP2 is shorted to enable the
comparator which drives LED1 and
LED2, JP3 is shorted to enable the main
oscillator and JP4 is shorted to enable
the AGC action of Q1.
I have designed a PCB for this project. The pattern can be downloaded as
a PDF from the Silicon Chip website.
Michael Harvey,
Albury, NSW. ($75)
siliconchip.com.au
This shows the sinewave and square wave outputs of the oscillator, which are
phase-locked. The sinewave appears quite pure and has low distortion.
Australia’s electronics magazine
December 2018 81
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(JAN 17)
kit including PCB and all SMD parts, LDR and blue LED
hard-to-get parts: Q8-Q16, D2-D4, 150pF/250V capacitor and five SMD resistors
$12.50
$35.00
VARIOUS MODULES & PARTS
LM4865MX amplifier IC & LF50CV regulator (Tinnitus/Insomnia Killer, NOV18)
$10.00
2.8-inch touchscreen LCD module with SD card socket (Tide Clock, JUL18)
$22.50
ESP-01 WiFi Module (El Cheapo Modules, Part 15, APR18)
$5.00
WiFi Antennas with U.FL/IPX connectors (Water Tank Level Meter with WiFi, FEB18):
5dBi – $12.50 ~ 2dBi (omnidirectional) – $10.00
NRF24L01+PA+NA transceiver with SNA connector and antenna (El Cheapo 12, JAN18)
$5.00
WeMos D1 Arduino-compatible boards with WiFi (SEPT17, FEB18):
ThingSpeak data logger – $10.00 ~ WiFi Tank Level Meter (ext. antenna socket) – $15.00
Geeetech Arduino MP3 shield (Arduino Music Player/Recorder, VS1053, JUL17)
$20.00
1nF 1% MKP (5mm lead spacing) or ceramic capacitor (Wide-Range LC Meter, JUN18)
$2.50
MAX7219 LED controller boards (El Cheapo Modules, Part 7, JUN17):
8x8 red SMD/DIP matrix display – $5.00 ~ red 8-digit 7-segment display – $7.50
AD9833 DDS module (with gain control) (for Micromite DDS, APR17)
$25.00
AD9833 DDS module (no gain control) (El Cheapo Modules, Part 6, APR17)
$15.00
CP2102 USB-UART bridge
$5.00
microSD card adaptor (El Cheapo Modules, Part 3, JAN17)
$2.50
DS3231 real-time clock with mounting spacers and screws (El Cheapo, Part 1, OCT16)
$5.00
MICROMITE PLUS EXPLORE 100 COMPLETE KIT (no LCD panel)
(SEP 16)
(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) (Cat SC3834)
$69.90
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 include GST where applicable. # P&P prices are within Australia. O’seas? Please email for a quote
12/18
PRINTED CIRCUIT BOARDS
NOTE: The listings below are for the PCB ONLY. If you want a kit, check our store or contact the kit suppliers advertising in this
issue. For 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 Online Shop has boards going back to 2001 and beyond.
For a complete list of available PCBs etc, go to siliconchip.com.au/shop/8 Prices are PCBs only, NOT COMPLETE KITS!
PRINTED CIRCUIT BOARD TO SUIT PROJECT:
PUBLISHED:
Li'l PULSER MK2 REVISED
JAN 2014
10A 230VAC MOTOR SPEED CONTROLLER
FEB 2014
NICAD/NIMH BURP CHARGER
MAR 2014
RUBIDIUM FREQ. STANDARD BREAKOUT BOARD
APR 2014
USB/RS232C ADAPTOR
APR 2014
MAINS FAN SPEED CONTROLLER
MAY 2014
RGB LED STRIP DRIVER
MAY 2014
HYBRID BENCH SUPPLY
MAY 2014
2-WAY PASSIVE LOUDSPEAKER CROSSOVER
JUN 2014
TOUCHSCREEN AUDIO RECORDER
JUL 2014
THRESHOLD VOLTAGE SWITCH
JUL 2014
MICROMITE ASCII VIDEO TERMINAL
JUL 2014
FREQUENCY COUNTER ADD-ON
JUL 2014
TEMPMASTER MK3
AUG 2014
44-PIN MICROMITE
AUG 2014
OPTO-THEREMIN MAIN BOARD
SEP 2014
OPTO-THEREMIN PROXIMITY SENSOR BOARD
SEP 2014
ACTIVE DIFFERENTIAL PROBE BOARDS
SEP 2014
MINI-D AMPLIFIER
SEP 2014
COURTESY LIGHT DELAY
OCT 2014
DIRECT INJECTION (D-I) BOX
OCT 2014
DIGITAL EFFECTS UNIT
OCT 2014
DUAL PHANTOM POWER SUPPLY
NOV 2014
REMOTE MAINS TIMER
NOV 2014
REMOTE MAINS TIMER PANEL/LID (BLUE)
NOV 2014
ONE-CHIP AMPLIFIER
NOV 2014
TDR DONGLE
DEC 2014
MULTISPARK CDI FOR PERFORMANCE VEHICLES
DEC 2014
CURRAWONG STEREO VALVE AMPLIFIER MAIN BOARD
DEC 2014
CURRAWONG REMOTE CONTROL BOARD
DEC 2014
CURRAWONG FRONT & REAR PANELS
DEC 2014
CURRAWONG CLEAR ACRYLIC COVER
JAN 2015
ISOLATED HIGH VOLTAGE PROBE
JAN 2015
SPARK ENERGY METER MAIN BOARD
FEB/MAR 2015
SPARK ENERGY ZENER BOARD
FEB/MAR 2015
SPARK ENERGY METER CALIBRATOR BOARD
FEB/MAR 2015
APPLIANCE INSULATION TESTER
APR 2015
APPLIANCE INSULATION TESTER FRONT PANEL
APR 2015
LOW-FREQUENCY DISTORTION ANALYSER
APR 2015
APPLIANCE EARTH LEAKAGE TESTER PCBs (2)
MAY 2015
APPLIANCE EARTH LEAKAGE TESTER LID/PANEL
MAY 2015
BALANCED INPUT ATTENUATOR MAIN PCB
MAY 2015
BALANCED INPUT ATTENUATOR FRONT & REAR PANELS MAY 2015
4-OUTPUT UNIVERSAL ADJUSTABLE REGULATOR
MAY 2015
SIGNAL INJECTOR & TRACER
JUNE 2015
PASSIVE RF PROBE
JUNE 2015
SIGNAL INJECTOR & TRACER SHIELD
JUNE 2015
BAD VIBES INFRASOUND SNOOPER
JUNE 2015
CHAMPION + PRE-CHAMPION
JUNE 2015
DRIVEWAY MONITOR TRANSMITTER PCB
JULY 2015
DRIVEWAY MONITOR RECEIVER PCB
JULY 2015
MINI USB SWITCHMODE REGULATOR
JULY 2015
VOLTAGE/RESISTANCE/CURRENT REFERENCE
AUG 2015
LED PARTY STROBE MK2
AUG 2015
ULTRA-LD MK4 200W AMPLIFIER MODULE
SEP 2015
9-CHANNEL REMOTE CONTROL RECEIVER
SEP 2015
MINI USB SWITCHMODE REGULATOR MK2
SEP 2015
2-WAY PASSIVE LOUDSPEAKER CROSSOVER
OCT 2015
ULTRA LD AMPLIFIER POWER SUPPLY
OCT 2015
ARDUINO USB ELECTROCARDIOGRAPH
OCT 2015
FINGERPRINT SCANNER – SET OF TWO PCBS
NOV 2015
LOUDSPEAKER PROTECTOR
NOV 2015
LED CLOCK
DEC 2015
SPEECH TIMER
DEC 2015
TURNTABLE STROBE
DEC 2015
CALIBRATED TURNTABLE STROBOSCOPE ETCHED DISC
DEC 2015
VALVE STEREO PREAMPLIFIER – PCB
JAN 2016
VALVE STEREO PREAMPLIFIER – CASE PARTS
JAN 2016
QUICKBRAKE BRAKE LIGHT SPEEDUP
JAN 2016
SOLAR MPPT CHARGER & LIGHTING CONTROLLER FEB/MAR 2016
MICROMITE LCD BACKPACK, 2.4-INCH VERSION
FEB/MAR 2016
MICROMITE LCD BACKPACK, 2.8-INCH VERSION
FEB/MAR 2016
BATTERY CELL BALANCER
MAR 2016
DELTA THROTTLE TIMER
MAR 2016
MICROWAVE LEAKAGE DETECTOR
APR 2016
FRIDGE/FREEZER ALARM
APR 2016
ARDUINO MULTIFUNCTION MEASUREMENT
APR 2016
PRECISION 50/60Hz TURNTABLE DRIVER
MAY 2016
RASPBERRY PI TEMP SENSOR EXPANSION
MAY 2016
100DB STEREO AUDIO LEVEL/VU METER
JUN 2016
HOTEL SAFE ALARM
JUN 2016
UNIVERSAL TEMPERATURE ALARM
JULY 2016
PCB CODE:
Price:
09107134 $15.00
10102141 $12.50
14103141 $15.00
04105141 $10.00
07103141
$5.00
10104141 $10.00
16105141 $10.00
18104141 $20.00
01205141 $20.00
01105141 $12.50
99106141 $10.00
24107141
$7.50
04105141a/b $15.00
21108141 $15.00
24108141
$5.00
23108141 $15.00
23108142
$5.00
04107141/2 $10.00/set
01110141
$5.00
05109141
$7.50
23109141
$5.00
01110131 $15.00
18112141 $10.00
19112141 $10.00
19112142 $15.00
01109141
$5.00
04112141
$5.00
05112141 $10.00
01111141 $50.00
01111144
$5.00
01111142/3 $30.00/set
SC2892
$25.00
04108141 $10.00
05101151 $10.00
05101152 $10.00
05101153
$5.00
04103151 $10.00
04103152 $10.00
04104151
$5.00
04203151/2 $15.00
04203153 $15.00
04105151 $15.00
04105152/3 $20.00
18105151
$5.00
04106151
$7.50
04106152
$2.50
04106153
$5.00
04104151
$5.00
01109121/2 $7.50
15105151 $10.00
15105152
$5.00
18107151
$2.50
04108151
$2.50
16101141
$7.50
01107151 $15.00
1510815
$15.00
18107152
$2.50
01205141 $20.00
01109111 $15.00
07108151
$7.50
03109151/2 $15.00
01110151 $10.00
19110151 $15.00
19111151 $15.00
04101161
$5.00
04101162 $10.00
01101161 $15.00
01101162 $20.00
05102161 $15.00
16101161 $15.00
07102121
$7.50
07102122
$7.50
11111151
$6.00
05102161 $15.00
04103161
$5.00
03104161
$5.00
04116011/2 $15.00
04104161 $15.00
24104161
$5.00
01104161 $15.00
03106161
$5.00
03105161
$5.00
PRINTED CIRCUIT BOARD TO SUIT PROJECT:
PUBLISHED:
PCB CODE:
Price:
BROWNOUT PROTECTOR MK2
JULY 2016
10107161 $10.00
8-DIGIT FREQUENCY METER
AUG 2016
04105161 $10.00
APPLIANCE ENERGY METER
AUG 2016
04116061 $15.00
MICROMITE PLUS EXPLORE 64
AUG 2016
07108161
$5.00
CYCLIC PUMP/MAINS TIMER
SEPT 2016
10108161/2 $10.00/pair
MICROMITE PLUS EXPLORE 100 (4 layer)
SEPT 2016
07109161 $20.00
AUTOMOTIVE FAULT DETECTOR
SEPT 2016
05109161 $10.00
MOSQUITO LURE
OCT 2016
25110161
$5.00
MICROPOWER LED FLASHER
OCT 2016
16109161
$5.00
MINI MICROPOWER LED FLASHER
OCT 2016
16109162
$2.50
50A BATTERY CHARGER CONTROLLER
NOV 2016
11111161 $10.00
PASSIVE LINE TO PHONO INPUT CONVERTER
NOV 2016
01111161
$5.00
MICROMITE PLUS LCD BACKPACK
NOV 2016
07110161
$7.50
AUTOMOTIVE SENSOR MODIFIER
DEC 2016
05111161 $10.00
TOUCHSCREEN VOLTAGE/CURRENT REFERENCE
DEC 2016
04110161 $12.50
SC200 AMPLIFIER MODULE
JAN 2017
01108161 $10.00
60V 40A DC MOTOR SPEED CON. CONTROL BOARD
JAN 2017
11112161 $10.00
60V 40A DC MOTOR SPEED CON. MOSFET BOARD
JAN 2017
11112162 $12.50
GPS SYNCHRONISED ANALOG CLOCK
FEB 2017
04202171 $10.00
ULTRA LOW VOLTAGE LED FLASHER
FEB 2017
16110161
$2.50
POOL LAP COUNTER
MAR 2017
19102171 $15.00
STATIONMASTER TRAIN CONTROLLER
MAR 2017
09103171/2 $15.00/set
EFUSE
APR 2017
04102171
$7.50
SPRING REVERB
APR 2017
01104171 $12.50
6GHz+ 1000:1 PRESCALER
MAY 2017
04112162
$7.50
MICROBRIDGE
MAY 2017
24104171
$2.50
MICROMITE LCD BACKPACK V2
MAY 2017
07104171
$7.50
10-OCTAVE STEREO GRAPHIC EQUALISER PCB
JUN 2017
01105171 $12.50
10-OCTAVE STEREO GRAPHIC EQUALISER FRONT PANEL JUN 2017
01105172 $15.00
10-OCTAVE STEREO GRAPHIC EQUALISER CASE PIECES
JUN 2017
SC4281
$15.00
RAPIDBRAKE
JUL 2017
05105171 $10.00
DELUXE EFUSE
AUG 2017
18106171 $15.00
DELUXE EFUSE UB1 LID
AUG 2017
SC4316
$5.00
MAINS SUPPLY FOR BATTERY VALVES (INC. PANELS)
AUG 2017
18108171-4 $25.00
3-WAY ADJUSTABLE ACTIVE CROSSOVER
SEPT 2017
01108171 $20.00
3-WAY ADJUSTABLE ACTIVE CROSSOVER PANELS
SEPT 2017
01108172/3 $20.00/pair
3-WAY ADJUSTABLE ACTIVE CROSSOVER CASE PIECES SEPT 2017
SC4403
$10.00
6GHz+ TOUCHSCREEN FREQUENCY COUNTER
OCT 2017
04110171 $10.00
KELVIN THE CRICKET
OCT 2017
08109171 $10.00
6GHz+ FREQUENCY COUNTER CASE PIECES (SET)
DEC 2017
SC4444
$15.00
SUPER-7 SUPERHET AM RADIO PCB
DEC 2017
06111171 $25.00
SUPER-7 SUPERHET AM RADIO CASE PIECES
DEC 2017
SC4464
$25.00
THEREMIN
JAN 2018
23112171 $12.50
PROPORTIONAL FAN SPEED CONTROLLER
JAN 2018
05111171
$2.50
WATER TANK LEVEL METER (INCLUDING HEADERS)
FEB 2018
21110171
$7.50
10-LED BARAGRAPH
FEB 2018
04101181
$7.50
10-LED BARAGRAPH SIGNAL PROCESSING
FEB 2018
04101182
$5.00
TRIAC-BASED MAINS MOTOR SPEED CONTROLLER
MAR 2018
10102181 $10.00
VINTAGE TV A/V MODULATOR
MAR 2018
02104181
$7.50
AM RADIO TRANSMITTER
MAR 2018
06101181
$7.50
HEATER CONTROLLER
APR 2018
10104181 $10.00
DELUXE FREQUENCY SWITCH
MAY 2018
05104181
$7.50
USB PORT PROTECTOR
MAY 2018
07105181
$2.50
2 x 12V BATTERY BALANCER
MAY 2018
14106181
$2.50
USB FLEXITIMER
JUNE 2018
19106181
$7.50
WIDE-RANGE LC METER
JUNE 2018
04106181
$5.00
WIDE-RANGE LC METER (INCLUDING HEADERS)
JUNE 2018
SC4618
$7.50
WIDE-RANGE LC METER CLEAR CASE PIECES
JUNE 2018
SC4609
$7.50
TEMPERATURE SWITCH MK2
JUNE 2018
05105181
$7.50
LiFePO4 UPS CONTROL SHIELD
JUNE 2018
11106181
$5.00
RASPBERRY PI TOUCHSCREEN ADAPTOR (TIDE CLOCK) JULY 2018
24108181
$5.00
RECURRING EVENT REMINDER
JULY 2018
19107181
$5.00
BRAINWAVE MONITOR (EEG)
AUG 2018
25107181 $10.00
SUPER DIGITAL SOUND EFFECTS
AUG 2018
01107181
$2.50
DOOR ALARM
AUG 2018
03107181
$5.00
STEAM WHISTLE / DIESEL HORN
SEPT 2018
09106181
$5.00
DCC PROGRAMMER
OCT 2018
09107181
$5.00
DCC PROGRAMMER (INCLUDING HEADERS)
OCT 2018
09107181
$7.50
OPTO-ISOLATED RELAY (WITH EXTENSION BOARDS)
OCT 2018
10107181/2 $7.50
GPS-SYNCHED FREQUENCY REFERENCE
NOV 2018
04107181
$7.50
1 x LED CHRISTMAS TREE
NOV 2018
16107181
$5.00
4 x LED CHRISTMAS TREE
$18.00
18 x LED CHRISTMAS TREE
$72.00
31 x LED CHRISTMAS TREE
$120.00
38 x LED CHRISTMAS TREE
$145.00
DIGITAL INTERFACE MODULE
NOV 2018
16107182
$2.50
TINNITUS/INSOMNIA KILLER (JAYCAR VERSION)
NOV 2018
01110181
$5.00
TINNITUS/INSOMNIA KILLER (ALTRONICS VERSION)
NOV 2018
01110182
$5.00
NEW PCBs
HIGH-SENSITIVITY MAGNETOMETER
USELESS BOX
FOUR-CHANNEL DC FAN & PUMP CONTROLLER
DEC 2018
DEC 2018
DEC 2018
04101011
08111181
05108181
$12.50
$7.50
$5.00
WE ALSO SELL AN A2 REACTANCE WALLCHART, RADIO, TV & HOBBIES DVD PLUS VARIOUS BOOKs IN THE “Books, DVDs, etc” PAGE AT SILICONCHIP.COM.AU/SHOP/3
Four-channel
High-current
DC Fan and
Pump Motor
Controller – Part II
by
Nicholas Vinen
In the October 2018 issue, we revealed our new high-current fan and pump
controller, able to switch up to 40A total with a 12V nominal supply,
controlling up to four loads using the readings from between one and four
temperature sensors. And it’s programmed over USB, to make the many
different settings easy to control. In this second part, we cover PCB assembly,
wiring it all up and adjusting those settings to suit your installation.
O
ne of the main goals with this new DC Fan Controller was to provide many different options to suit
different situations, without making it a nightmare
to configure. We certainly couldn’t use jumpers and trimpots because there would be just too many and it would be
too hard to make any changes once the unit was mounted
in a vehicle.
So instead, we have made the unit configurable and
controllable over a USB text interface. Unfortunately, the
low-power micro we’ve chosen doesn’t have a great deal of
memory but we’ve come up with a way to provide a friendly user interface that allows you to see the exact settings
and make changes via a laptop or desktop PC.
Basically, you view and change your settings via a web page
which then produces a “magic string” of text which, when
pasted into the Fan Controller’s terminal, changes its behaviour to match up what you have entered on the web page.
So if you aren’t happy with the way your fans and/or
pumps are being operated, it’s a simple matter to reach
84
Silicon Chip
the accessible USB plug or socket you’ve fitted, connect it
to your PC and upload a new configuration. You can even
test it without having to take the vehicle out on the road,
simulating battery voltage and changes and temperature
sensor changes to see what happens.
The PCB itself has been made reasonably compact to
make fitting it inside the vehicle easier, by using mostly
SMD parts. Despite this, it’s a bit larger than our last solo
Fan Controller (January 2018), so you’ll need a bigger box
and it’s a bit trickier to find somewhere to fit. But we did
find a good location in the packed engine bay of our test
vehicle and the wiring is pretty easy, once you’ve purchased appropriate connectors and gotten the hang of soldering them.
And anyway, it’s heaps more capable and configurable,
so the small penalty in size is well worth it.
PCB construction
The Fan Controller is built on a PCB coded 05108181,
Australia’s electronics magazine
siliconchip.com.au
FAN1
FAN2
FAN CONTROLLER MK2 MODULE
1
OUTPUT 4
D3
FAN3
FAN4
221
D6
PTC1
10 F
1
1 F
CON3
22 F
10kΩ
CON5 - TS2
10kΩ
THERMISTORS
CON6 - TS3
18B20
CON7 - TS4
18B20
CON12
DISABLE
ON
OFF
TEMP
SENSORS
SC
20 1 9
Fig.4: this diagram shows where each part is fitted to the PCB and
also gives an example of how to wire the unit up. Most installations
will not use all of the connections shown. Be sure to get the supply and output polarities right – the positive leads go to the pads closest to the board edge. You can mix
and match the temperature sensor types; those shown here are just one possibility.
which measures 68 x 34.5mm. All the components are
mounted on the top side. Use the PCB overlay diagram,
Fig.4, as a guide during assembly.
If you are fitting onboard USB socket CON1, start with
that. Spread a thin smear of flux paste on its four mounting pads and five signal pins, then drop the socket on the
board and move it around until the two plastic posts on
the underside drop into the alignment holes. You should
find its five pins are then positioned over the pads.
Nudge it a little if necessary, to get the alignment perfect. Then apply solder to one of the four large pads which
attach its “feet”. You will need to apply a fair bit of heat
and some extra solder to get a good, solid joint. Re-check
the signal pin positions and if necessary, reheat that solder
joint and carefully nudge the part without lifting it up. It
may be hot, so use caution.
Once you’re happy with the position of the signal pins,
solder the other three mounting feet, then apply a small
amount of solder to those pins. If you load some solder
onto the tip of your iron and touch it to the end of the pin
(which is partially hidden under the body), the flux paste
you applied earlier should help to ‘suck’ the solder off the
iron and onto the pin and pad.
Repeat this for the other four signal pins and carefully
examine them under a magnifier with good light, to ensure
a good joint has formed and there are no bridges between
pins. If there are bridges, apply a little extra flux paste and
then use solder wick and heat from the iron to remove them.
Next, move onto microcontroller IC1. It is in a wide SOIC
package with relatively large pin spacings, so it is not difficult to solder. First, find its pin 1 dot and make sure that
it is orientated as shown in Fig.4. Also, check that it is sitting flat on the board, then tack solder one of its corner
pins. It’s easier to solder if you spread a small amount of
flux paste on all its pads first.
Make sure all the pins are correctly aligned on their pads.
If not, heat that initial solder joint and gently nudge it into
position. Repeat until you are happy that they are all lined
up, then solder the remaining pins and finally, add a little
extra solder to the first pin to refresh the joint. Inspect the
joints and as before, if you find any bridges, clean them up
with flux paste and solder wick.
Now you can proceed to solder IC2, IC3 and REG1 similarly, as they are all in smaller SOIC packages. Note though
that their pin 1 dot is orientated differently to IC1. Check
the orientation carefully against what is shown in Fig.4
siliconchip.com.au
220Ω
REG2
100nF
CON4 - TS1
1S
1A FUSE
10kΩ
4.7kΩ 4.7kΩ 4.7kΩ 4.7kΩ
OUTPUT 3
1
CON2 ICSP
D4
Q2
GND D+ D- VCC
100kΩ
220Ω
POWER
TVS1
10-40A BLADE FUSE
1nF
12V
BATTERY
1kΩ
–
D1 100nF
IC3
+
470nF
1
1kΩ
100nF
1kΩ
D5
CON1
220Ω
1
39kΩ
Q4
OUTPUT 2
IC1
PIC 16F1459
IC2
Q1
CON13 - LED
D7
Q3
REG1
100nF
OUTPUT 1
10kΩ LED1
100kΩ
D2
The completed motor/pump controller is shown here
slightly oversize for clarity (actual PCB size is 68mm wide
– as seen above). Yes, it is all SMD components so a good
eye, a steady hand and a fine-tipped iron are all required.
before soldering each chip.
Mosfets Q1 and Q2 should be fitted next. These are in a
similar package to IC2, IC3 and REG1 except that the pairs
of pins on one side are joined together. So we have provided larger pads to solder those pairs of pins to the board.
Again, check that the pin 1 dot is orientated correctly –
the same as IC2 and IC3 – before soldering them in place.
These are seven small three-pin SOT-23 package pards
on the board: Q3, Q4, D5-D7 and REG2. They look similar
so don’t get them mixed up. Their pins are widely spaced,
so they are pretty easy to solder. Use the same technique as
with the ICs; it’s generally easier to tack the pin that’s all
by itself on one side first, then solder the other two pins
and refresh the first solder joint last.
Now fit the smaller (3216/1206-size) resistors and capacitors. The required values and positions are shown in Fig.4.
They are not polarised, so orientation is not important. The
resistors will be printed with a 3-digit or 4-digit code on
the top to indicate their value, while the ceramic capacitors will be unmarked so be careful not to mix them up.
It’s the same basic method – tack one end, check the
positioning and then solder the opposite side and go back
and refresh the first joint.
Besides making sure the parts are flat on the board and
that the solder joints are made properly, the main trick is
to be patient and wait several seconds between soldering
one side of the part and the other. This gives the joint time
to solidify. Otherwise, the part will tend to move out of position when you touch it with the iron.
Australia’s electronics magazine
December 2018 85
You can now fit PTC1 and the large 220 resistor next to
it, using the same basic technique. Keep in mind that these
larger parts will require a bit more heat and solder to form
good joints. Neither of these components are polarised.
The diodes are also two-terminal devices and can be
soldered in the same manner as the passives but are larger
again so they will also need a bit more heat. Fit diodes D1D4 now, ensuring that their cathode stripe faces towards
the right side, ie, into the middle of the board. You can also
fit TVS1 now; it’s larger again but otherwise is similar to
the other diodes.
The last remaining SMD component is the 22µF tantalum capacitor next to REG1. It is also polarised and must
be soldered with its positive end (generally marked with
a stripe) towards the bottom edge of the board.
You can now move on to fit the headers that you require
for your application. You will need at least one of the four
temperature sensor headers (CON4-CON7); we recommend
that you fit all four, even if you aren’t planning to use them,
in case you want to add more sensors later.
You can also fit CON12 and/or CON13 now, for the enable/disable control and indicator LED. Again, you may
want to fit them even if you aren’t planning to use them,
Parts list – Fan/Pump Controller
for sample installation with one fan and three
temperature sensors (change to suit yours)
1 DC Fan/Pump Controller PCB Mk2, fully assembled
1 IP65-rated sealed high-temperature ABS box,
15x65x40mm [Jaycar Cat HB6122]
1 USB mini-B to type-A cable
2 30A waterproof blade fuse holders with LED
[Jaycar Cat SZ2042]
1 1A blade fuse [Jaycar Cat SF2126]
1 20A blade fuse [Jaycar Cat SF2138]
2 6mm non-insulated eye terminals [Jaycar Cat PT4934]
1 4-way Deutsch waterproof plug/socket set
[Jaycar Cat PP2149]
1 2-way Narva-style waterproof plug/socket set
[Jaycar Cat PP2110]
1 4-way Narva-style waterproof plug/socket set
[Jaycar Cat PP2114]
1 2-way 250-series automotive socket (to suit radiator fan)
Jaycar Cat PP2062]
1 1m length 2-core 7.5A automotive cable
[Jaycat Cat WH3057]
1 1m length 2-core 15A automotive cable
[Jaycar Cat WH3079]
1 1m length 2-core 25A tinned automotive cable
[Jaycar Cat WH3087]
1 1m length 25A black tinned automotive cable
[Jaycar Cat WH3082]
1 1.2m length 10mm diameter clear heatshrink tubing
[Jaycar Cat WH5555]
2 DS18B20 digital temperature sensors in waterproof
housings [SILICON CHIP cat SC3359]
1 10k lug-mount NTC thermistor [Altronics Cat R4112]
3 2-pin polarised headers, 2.54mm pitch, with pins [Jaycar
Cat HM3402]
2 M6 copper crinkle washers
2 M6 hex nuts
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Silicon Chip
in case you change your mind later.
Planning the wiring
As mentioned in the first article (October 2018), rather
than use connectors for the high-current wiring, we have
simply provided large pads on the board, to which fairly
thick wires can be soldered directly. While it is possible to
use fixed cables, we suggest that you use in-line connectors on most or all of the wires.
This has a few advantages: it makes testing easier, it
makes it easier to replace a sensor or fan later if you have
to, it makes it easier to remove the unit in case you need
to repair or reprogram the unit, and so on.
There are various suitable types of inline automotive
connectors, many of which are waterproof. While waterproof connectors are not critical for the 12V supply wiring
or connections to fans/pumps, we recommend that you use
them for the sensors, enable/disable line and external LED
wiring (if used) as water may conduct enough current to
affect the function of those devices.
See the panel below for more details on suitable connectors that are available.
Having decided where you will have connectors and what
type to use, you will then need to find a suitable location
for the case that will house your PCB. We strongly suggest that you use an IP65 (or better) rated waterproof box.
You could use an ordinary plastic box and waterproof
it with silicone but it will be hard to get it apart later if
you need to.
We used a sealed ABS plastic box from Jaycar – see the
additional parts list (at left) for details. Figure out where
your box will fit in the vehicle and also how you will attach it. We used a screw through one of the box’s two integral mounting holes, through a support member in the
vehicle (which already had a hole in it) and into a piece
of foam, capped off by a washer and a nut.
We also placed a thin piece of foam (with a hole in it)
between the box and the cross member. This provides
some vibration reduction compared to rigidly mounting
it to the vehicle.
Now that you have a location for the box, you can measure the lengths of all the required cables.
The easiest way to measure how long a cable needs to be
is to thread a spare piece of wire through the vehicle between the two points to be connected, loosely, then pinch
the end in one hand, pull it out and measure its length.
Remember that some parts of the car may flex or move, so
don’t make it too tight.
You will also need to calculate the minimum current
rating for each. This will typically be 10-20A for fan cables and 10-40A for the battery cables. Just about any wire
can be used for the sensor wiring, enable/disable switch,
LED and battery voltage sense wiring, as these all carry
mere milliamps.
When cutting the cables to length, remember to account
for the length lost stripping both the inner and (where present) outer layers of insulation, plus a bit extra in case you
damage the wire while stripping it and have to cut it off.
Having cut and stripped the insulation off the ends of all
the various cables required, crimp and/or solder the connectors on. Leave the connectors that will plug into the
PCB off for the moment.
Don’t forget to make provision for some heatshrink tub-
Australia’s electronics magazine
siliconchip.com.au
There’s not a huge amount of space under the hood of many cars, especially a big V8! Choose a location that doesn’t
interfere with the operation of any other controls and, preferably, is easy to get to! Ensure all wiring is adequately secured.
ing for any multi-wire or multi-cable bundles, to keep everything neat when you run them later.
Configuration and testing
It’s a good idea to test the unit before making the final
connections since if you find any problems later, it will be
harder to fix them if the unit is already captive in its case
due to wires soldered directly to the board.
You will need to load it with its initial configuration. All
you need to do this is a computer with a USB port and a serial terminal program such as Tera Term Pro (a free download from https://ttssh2.osdn.jp/index.html.en).
You also need an internet connection, although it doesn’t
necessarily need to be available at the same time that the
computer is hooked up to the unit; you can prepare the
configuration beforehand.
Start by plugging the finished board into your computer
using either a Type-A to mini Type-B USB cable (if you fitted CON1) or a chassis-mounting Type-B socket wired into
CON3, plus a suitable cable.
Check that your computer has detected a new USB serial device. That verifies that the microcontroller is working
correctly. In Windows 10, you can do this by right-clicking
on the Start button, choosing “Settings” from the menu that
appears, then clicking on the Devices icon. You should see
a device listed with a name like “USB Serial Port (COM5)”.
The COM number will vary.
Open this serial port using your chosen terminal emulator and then type “status” and press Enter. You should
get a status display similar to that shown in Fig.6. If you
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don’t, check your port settings (the baud rate setting and
so on are not important).
If you can’t get any response, you may have a wiring or
hardware fault, so check that your USB socket is soldered
and wired correctly, that the PIC chip (IC1) is properly programmed and soldered and that all associated components
have been fitted correctly.
Once you’ve established communications with the chip,
open a web browser and go to http://siliconchip.com.au/
apps/DCFanMk2 This page will help you set up a basic
configuration for the unit, for further testing.
See the panel on Settings for help on how to set the unit
up initially. The web page referred to above translates your
desired settings into an encoded string which you can send
to the Fan/Pump controller, setting its configuration to the
desired state. Read up on the basic settings now – you can
ignore the more advanced settings for now.
You can read about them later, once you’ve established
that everything is working.
Loading the configuration
Once you have selected all the options you want, click
the “Copy to clipboard” button at the bottom of the window, then switch to your terminal program and paste the
configuration string (which is now in the system clipboard)
into the terminal. You can do this in Tera Term Pro by
right-clicking in the terminal window, then pressing Enter.
You should get a response that says “OK”. If it says “Error”, then the clipboard string has somehow become corrupted.
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December 2018 87
Explanation of Settings
Basic Settings
The settings user interface (available at
http://siliconchip.com.au/apps/DCFanMk2) is shown in Fig.5. Note that this has
been revised slightly since the October article, to remove some unnecessary features
and add some other useful ones. Start by
using the top four drop-downs to select
the type of temperature sensors you have
hooked up to CON4-CON7.
The following three voltage thresholds
control how the unit responds to changing
battery voltages. The defaults are sensible,
so you don’t necessarily need to change
them.
The first determines the voltage the battery needs to rise above before the unit will
become active.
The second determines the voltage it
must fall below when active to terminate normal operation and enter cool-down mode,
an optional time during which the fans and/
or pumps will continue to run, possibly with
reduced duty cycles.
The third voltage threshold prevents cooldown mode from flattening the battery. If
the battery voltage falls below this during
cool-down mode, the unit will immediately
go into sleep mode and wait for the battery
voltage to rise above the switch-on threshold before becoming active again.
The cool-down delay is designed so that
vehicles which charge the batteries sporadically will not enter cool-down straight away
when the battery is no longer being charged.
The battery voltage must be below the “Enter
cool-down” threshold for this long before it
will go into cool-down mode. For vehicles
which continuously charge the battery, set
this to a short time (eg, 1s).
The minimum cool-down on-time sets
the minimum time that the unit must be in
full operation before it goes into cool-down
mode. If the battery voltage is above the
threshold for a shorter time than this, the
unit will immediately shut down instead.
The cool-down time is the maximum
number of seconds that the unit will spend
in cool-down mode before shutting down.
Cool-down compensation allows you to
reduce the fan/pump duty cycles in cooldown mode, compared to what they would
be during normal operation given the sensor temperatures. Upon entering cool-down
mode, the duty cycles are immediately multiplied by the maximum value of this setting.
So if that is 75%, they will drop by 25%. The
minimum duty cycle setting for each output
will still be in effect.
As the battery voltage drops towards the
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shut-down threshold, the duty cycle multiply
value approaches the lower value of the setting. So with the default values, duty cycles
will reduce from 75% of nominal to 25% of
nominal before the unit shuts off completely.
Per-output settings
Each output has a similar configuration entry in the table beneath the global settings. You
can enable or disable each output individually
using the drop-downs at left. You can also set
output #2 to be a slave to #1 so that the two
outputs can be paralleled to give a single 20A
output. The same comment applies for outputs #3 and #4.
The PWM frequency must be the same for
outputs #1 and #2 and the range of possible
frequencies is shown on-screen, along with the
closest frequency to the one you have selected,
which will be the actual frequency used. Note
that the real frequency will also vary slightly
depending on the micro’s oscillator calibration.
The frequencies for outputs #3 and #4 can
be set independently but only if one of them
is 10Hz or less. The maximum frequency setting for these two inputs is 2kHz. Typically,
you would only use two different frequencies
if one of these outputs is controlling a pump
and you want it to be driven with long pulses.
In this case, you can choose a frequency as
low as 1/10Hz (100mHz).
The duty cycle for the output is determined
by three main parameters: the duty cycle range,
the temperature range and the way the sensor
data is combined. The lowest duty cycle in the
range given will occur when the sensor reading
is at the lowest temperature specified, and the
highest duty cycle will occur when the sensor
reading is at the highest temperature specified.
In other words, if you set the duty cycle
range to 40-60% and the temperature range
to 20-30°C, you will get a duty cycle of 40%
at 20°C, 42% at 21°C, ... 58% at 29°C and
60% at 30°C.
In the simplest case, this temperature is
derived from a single sensor. This is the default; you will find that initially, the duty cycle
of output 1 is derived from TS1, of output 2
from TS2 and so on. But you can change this
mapping. Multiple outputs can use the same
sensor if desired.
The final setting we’ll describe here is the
ramp rate, which specifies the minimum number of milliseconds that it takes for the output
duty cycle to change by 1%. So if you set this
to, say, 100ms then a change from 0% to 100%
duty cycle will take 10 seconds.
Advanced Settings
The Curve setting for each output allows you
Australia’s electronics magazine
to compensate for loads where the speed/
power is not directly proportional to voltage, linearising their speed to temperature
relationship. For example, if you have a fan
where speed is proportional to the cube of
the average voltage across it, use the Cube
Root setting to provide a more linear speed
with temperature.
SVC stands for Supply Voltage Compensation and allows the duty cycle to be automatically dialled back as the battery voltage increases, providing a constant voltage/
speed for a given input temperature. Simply
specify the voltage at which you want this to
take effect (eg, 12V). If the supply voltage
is, say, 13V then the duty cycle will be reduced to 12/13 of nominal to give the same
average voltage across the load.
Advanced temperature formulas
To the right of the sensor name, you will
see a minus sign and then a drop-down box
containing zero.
You can select a different number to offset the sensor reading or, more usefully, you
can select a second temperature sensor to
make a differential reading. The temperature settings you enter for “Temperature
range” then refer to the difference between
the two sensors.
Rather than using a single sensor on either side of the minus sign, you can instead
change the blank dropdown in front of it to
read “min” or “max” and this will let you
select a second sensor.
The temperature used in the calculation
will then be the lowest (min) or highest
(max) of the two readings. Or you can make
one of the values a constant; the temperature sensor reading will then be clamped
when it goes below (min) or above (max)
that value. That feature is most useful in the
differential sensing mode.
So effectively, you can build a simple formula to derive the temperature reading from
up to four sensors, rather than just using
the temperature from one sensor directly.
There is one additional option; you can
actually have TWO such formulas, using the
same structure (but they can be different).
The unit will calculate both values and
then the result will be either the lowest (min),
highest (max) or average (avg) of the result.
That gives you a further way to combine
multiple temperature readings.
To enable that option, click on the first
black drop-down in the temperature measurement box and change it to one of the three
other options. The second formula will then
appear, and you can fill it in.
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Immediately after pressing Enter, the new configuration
takes effect. Type “show status” and press Enter and you
may see some changes already.
Initial testing
You can now use the “override” command to perform
some basic checks on your settings. The override command
lets you ask the unit to pretend that the supply voltage or
temperature sensor readings are a particular value, so you
can see what happens without actually having to vary the
supply voltage or heat up or cool down the sensors.
This is useful both when the unit is installed in the vehicle (since you can’t always get the sensors to read what
you want while idling) but also at this early stage, to avoid
the need for variable voltage sources and variable resistors.
First, run the “status” command (type “status” and press
Enter). Since the unit has no 12V supply, it should give a
supply reading close to 0V and it should indicate that it is
in sleep mode as a result. Now issue the command “override supply 14.4V” (or similar). Re-run the status command.
You should see that the supposed supply voltage has increased and that the unit is now in run mode.
However, since it knows there is no 12V supply, it will
not drive the Mosfets, to protect the driving circuitry (which
runs off the currently non-existent 12V supply).
Still, you can see what PWM duty cycle the unit will
drive each output to for the current temperature sensor
inputs. You can then issue a command like “override TS1
47.5C” to make it pretend that temperature sensor #1 is actually at 47.5°C, rather than its actual current temperature.
Re-run the status command and observe how the output
duty cycle(s) change.
You can then override other sensor temperatures, or
change the existing one, to see what happens. If it isn’t
working as expected, review your configuration and repeat
the procedure above to load the new configuration into the
unit, then continue testing in this manner. See Fig.6 for an
example where the override feature is used.
Once you have finished testing, issue the “override clear”
command and the unit will go back to working as usual.
You can then proceed to connect actual loads if you
want – they don’t have to be fans, a 12V LED would work
and would give you an easy way to see how the duty cycle changes.
Having said that, since your fan(s) will already have the
right connectors, it may be easiest to use them for testing.
Just make sure you have them in a safe location so that
when they are powered up, they don’t fall over and the
Fig.5: a screen grab of the latest version of the web-based configuration interface. The upper section allows you to
configure the temperature sensor types, supply voltage thresholds, timing parameters and cool-down mode settings. The
lower section controls the relationship between sensor temperature and duty cycle for the four outputs. In this example,
outputs #1 & #2 are combined to control a single 20A fan, based on the temperature of three sensors.
siliconchip.com.au
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December 2018 89
Common automotive connectors
Deutsch connectors
We have used two different types of waterproof connector on our
prototype. For the two DS18B20 sensors, we used a single 4-pin
Deutsch plug and socket set (Jaycar Cat PP2149). This was cheaper
than two 2-pin plugs and sockets (Jaycar Cat PP2150). A 6-pin version is also available (Cat PP2148).
Deutsch connectors are used widely on vehicles and are known to
be reliable, with a typical current rating of 13A/pin. They are relatively
easy to put together, although there are a few steps, and ideally, you
should use a specialised crimping tool (but you can get away without
it). Jaycar sells an appropriate tool, Cat TH2000, which also requires
a Deutch die set (Cat TH2011).
First, if the wires you will be attaching to the connectors are part
of a multi-core cable, you will need to strip back about 20mm of the
outer insulation to expose enough wire to feed into the connectors.
You need to strip about 3mm of insulation away from the end of
each wire to crimp into the pins later.
Both the plug and socket have a thick gasket inserted into the rear,
with a small hole for each wire. The first step is to carefully prise this
out of each shell and then push wires through these holes. If your
wire is particularly thin (as is the case with the waterproof DS18B20
sensors), use heatshrink tubing to make the wire diameter larger so
it will seal properly when pushed through.
The next step is to crimp the wires onto the pins. One set has
pointed ends and the other set have cups in the end, which accept
the pointed ends of the other pins. The cupped pins are larger so you
can figure out which shell they go into by checking for the one with
the slightly larger holes.
Once you’ve figured out which pins will go on which wires, fold the
larger metal leaves around the wire insulation, crimping them to hold
the wire in place. Next, fold the smaller leaves around the exposed
copper. A Deutsch crimping tool will do all this in one step but if you
don’t have one, you can use small pliers (ideally with angled ends)
to carefully fold the leaves around the wire and clamp it down hard.
It isn’t ideal but it works.
The trick to doing this is to make sure that you don’t just squish
the leaves flat, as they will tend to spread out and make the pin too
wide. You also need to compress them horizontally, so that the final
crimp is compact.
We also like to add a little flux and then solder to the top of the
exposed wires to ensure good electrical contact, but that technically
shouldn’t be necessary if the wires have been properly crimped (but
that’s quite tricky to get right if the wire is very thin).
Once all the pins are soldered, push them into the rear of each
housing until you hear them click into place. For the cupped pins, you
will know they have been pushed home because their ends will be flush
with the front of the connector.
For the pointy pins, it can be quite hard to push them in (especially
with the gasket in the way), so you may find it easier to push them in
part way and then grab them from inside the front of the shell using pliers, and pull them forward until they lock in place.
Now all you need to do is push both gaskets back into the rear of each
shell, making sure that they sit flush with the rear of the connector all
around the edge, then push the flat orange plastic piece into the end of
the socket (ie, the shell with the cupped pins) until it locks into place.
This stops the sealing gasket from being pulled off when you withdraw
it from the plug later.
The green plastic wedge pushes into the end of the plug and locks in
place in a similar manner.
Narva connectors
This is another type of multi-pin waterproof automotive connector, rated
at 20A/pin. They are a bit more expensive than a Deutsch connector but
have a higher current rating. Jaycar sells these in 2-pin (Cat PP2110),
3-pin (Cat PP2112), 4-pin (Cat PP2114) and 6-pin (Cat PP2116) versions.
We have used two in our set-up; one 2-pin version for the NTC thermistor on the intercooler radiator, mainly because we already had a suitable plug wired to the existing thermistor in the vehicle, and a 4-pin version to connect the unit to the battery.
Its 20A rating is sufficient for our installation as only one fan is being driven, and the four pins mean we can connect both pairs of battery
wires in a single plug/socket.
One of the disadvantages of this type of connector is that the socket
pins are a bit sloppy and so plugging the two pieces together can be a
bit of a chore. But once the pins find the cups, they all lock into place.
Assembling these is similar to the Deutsch connectors but there are
some differences. Rather than one large rubber gasket at the rear, there
are individual gaskets for each wire, so you need to remember to push
these over the wires before crimping the pins (although they can be
pushed over the pins if you’ve forgotten).
Both the plug and the socket have a section at the rear which unclips
and swings out, to allow you to insert the pins, which click into place.
You then push the gaskets in, leaving the small central section sticking
out, then swing the rear back into place and latch it using the plastic
clips. This prevents the gaskets from falling out.
You can tell which is the plug and which is the socket since the socket
(which takes the cupped pins) has larger entry holes and is overall deeper.
Note that the gaskets will fit wire rated at around 15-20A. Thinner
Both the Deutsch (left) and Narva (right) connectors
are waterproof and are available with various
numbers of pins, from 2 to 47(!).
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gauge wire will need to have heatshrink added to form a proper seal
while larger gauge wire (~25A) cannot fit through the gaskets (and
will only just fit in the connector). You will need to use silicone sealant if you need connectors with heavy duty wiring to be waterproof.
Overall, we suggest that you stick with Deutsch connectors unless your application exceeds their 13A/pin current rating as they are
easier to use.
Non-waterproof options
Chances are your fans/pumps will already have a plug and it will be
easier if you can find a matching plug rather than cut off the existing one
and attach a new one or hard-wire it (although that’s certainly feasible).
Our fan already had a “250-series” two-pin connector and these
are available from Jaycar too; they sell 2-pin (Cat PP2062), 3-pin (Cat
PP2064), 4-pin (Cat PP2066), 6-pin (Cat PP2068) and 8-pin (Cat
PP2069) versions.
Make sure you use wire with a high enough current rating to suit
your fan. Keep in mind the fan’s specified nominal current may be for
a 12V supply, and it could draw around 30% more current at 14.4V
when the battery is being charged.
Another option for high-current connections, especially to the battery, is Andersen connectors, which are also available from Jaycar.
These are available in a range of current ratings including 35A, 50A,
75A, 120A, and175A. These are dual “genderless” connectors (ie, two
identical connectors will plug into each other).
Individual Anderson connectors are also available, with lower current ratings.
The 50A connectors are quite large but are probably the
best choice for battery connections requiring 30-40A. The lower rated connectors will not accept thick wire and are challenging to assemble, whereas the 50A and up versions feature a “solder cup” which you can fill with liquid solder and then push the
wire into, making them relatively straightforward to put together.
We used the
250-series (right)
plug because that’s
what our radiator
had fitted. The
two-way Narva
connector (below)
was used because
it had a higher
current rating
(20A). There are
several other types
available.
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spinning blades won’t hit anything.
You will also need to connect the sensors (if not already
connected) and a 12V power supply with sufficient current
capability for further testing. This could be your car battery. You can also use the override command in live testing.
It’s also a good idea to check that the sensors are actually
working, rather than just relying on the override command.
Test each sensor by heating it up or cooling it down slightly, then re-run the status command and check that the temperature reading from that sensor has changed as expected.
You can use a hot air gun, some ice, a cigarette lighter
etc. Just make sure if you are heating the sensor that you
don’t overheat it or anything nearby.
For example, if using a lighter, keep the flame some distance below the sensor and don’t heat it for more than a
few seconds.
You may also be able to observe the fans/pumps being
driven, depending on whether you’re pushing the sensor
temperatures into the ranges where those loads are activated.
Preparing the case
Now you need to figure out where each wire is going to
enter the case. Try to keep in mind the layout of the pads
and connectors on the PCB, ie, avoid wires crossing all
over the place inside the box, if possible. Mark and drill
the holes required to get those wires into the case. Don’t
make the holes any larger than necessary.
Solder the fan/pump and power supply wires onto the
pads, in the locations shown on Fig.4. It helps to pull these
as far into the box as necessary, so you can do the soldering outside the box, then pull the wires back out when
you have finished.
The other connections are made with polarised plugs.
Depending on the sizes of the holes you’ve made, you may
be able to crimp/solder these onto the wires and then feed
them through the holes, then push them into the plastic
plug blocks. If they don’t fit through the holes, you will
have to feed the wires through first and then crimp/solder
the pins afterwards.
Note that the LED and any DS18B20 temperature sensor
wires are polarity sensitive, so make sure you refer to Fig.4,
so you get them on the right side of each plug. The enable/
disable and any NTC thermistor wiring is not polarity sensitive so the pins can go into the plugs either way around.
While it isn’t necessary to bring the USB connector outside the case – you could just open up the case and plug
in a cable if you need to change the way the unit operates
– it’s certainly more convenient to have it available from
the outside.
This is especially true if the unit is going to be buried
behind panels or under other bits of the vehicle.
We’ve provided the option to fit a waterproof USB socket on the outside of the case and connect it via pin header
CON3. Simply wire up the USB socket pins as per Fig.4 –
the standard USB wire colour codes are shown there too.
But in many cases, it will be easier to feed a micro-B to
Type A USB cable through a hole in the box and plug it
into CON1 on the board, then seal up the hole with silicone sealant.
Tuck the USB plug away somewhere that it won’t get
splashed with too much water and tie it up with a twist
tie or two so that you can easily remove it and plug it into
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December 2018 91
List of USB serial terminal commands
status - shows the unit’s current status, including sensed
battery voltage, sleep/cool-down/active state, sensor
temperatures, PWM output duty cycles and override
status.
Fig.6: this shows how you can use the override command
in the USB serial terminal to test the unit. You can set
pretend supply voltages and sensor temperatures and
observe how this changes the output duty cycles. If you
have fans and a power supply connected, their speeds will
change as if the sensor temperatures have changed to the
values given.
a laptop later if you need to reconfigure the unit.
dump - displays the unit’s configuration string (including
restore command) on the console. This can be pasted
into the web app to retrieve the current configuration.
restore - when followed by a base64-encoded string of the
appropriate length, updates the unit’s configuration in
RAM with the new settings (get this from the web app).
save - saves the current configuration in RAM to flash,
so it is retained the next time power is cycled. Usually
used after a restore command.
That’s the approach we took in our installation
revert - loads the configuration from flash into RAM,
overwriting any changes which have been made but
Once you have fed all the wires in through the holes
not saved since power-up.
you’ve made in the box, solder and/or plug them into the
ILICON
HIPoutputs to get
board where required.
If you’re paralleling
Gives
instant
calculation
of a short wire link beoverride supply xx.xxV - pretend that the supply voltthe
20Ayou
current
rating,
you can run
age- isFrequency
the specified value until cleared.
Inductance
- Reactance
Capacitance
tween
the negative pads
for the master and-slave
outputs.
There’s no need to link the positive pads since they all join
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con$20.00 inc P&P & GST ORDER NOW AT www.siliconchi p.com.au/shop $10.00 inc P&P & GST
You can then locate it in your vehicle, in the place de- venient, out of the way but where you can easily reach it
termined earlier, and tie it down using screws, cable ties once any panels are back in place that you have removed,
or any other method you see fit.
in case you need to adjust the settings later.
As we said, it’s a good idea to place some springy foam
Now all that’s left is to go for a drive and make sure that
or rubber between the case and the vehicle to provide some everything is working as expected! If you want to leave a
vibration isolation. We used one of the case’s two water- laptop plugged in while driving (eg, via a USB extension
proof screw mounting holes to attach it to a cross member cable), that’s OK, just make sure it’s routed in a safe manin the vehicle.
ner (ie, don’t leave the bonnet open while driving) and get
After another quick check to make sure everything is a passenger to monitor the sensors and fans via the “staworking, screw the lid on (including the waterproof gasket) tus” command.
SC
The S
C
READY RECKONER
It’s ESSENTIAL For ANYONE in ELECTRONICS
The SILICON CHIP READY RECKONER
Gives you instant calculation of
Inductance - Reactance - Capacitance - Frequency
It’s ESSENTIAL For ANYONE in ELECTRONICS
You’ll find this wall chart as handy as your multimeter – and just as useful!
Whether you’re a raw beginner or a PhD rocket scientist . . . if you’re building, repairing, checking or designing
electronics circuits, this is what you’ve been waiting for! Why try to remember formulas when this chart will
give you the answers you seek in seconds . . . easily! Read the feature in the Januar y 2016 issue of SILICON CHIP
(you can view it online) to see just how much simpler it will make your life!
All you do is follow the lines for the known values . . . and read the unknown value off the intersecting axis.
It really is that easy – and fast (much faster than reaching for your calculator!
Printed on heavy (200gsm) photo paper Mailed flat (rolled in tube) or folded Limited quantity available
Mailed Folded:
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92
Silicon Chip
Australia’s electronics magazine
HU
420x59G4Em
on heavy
photo pa
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per
siliconchip.com.au
Vintage Radio
By Associate Professor Graham Parslow
AWA 1948 compact
portable model 450P
The AWA Radiola 450P is quite unusual
for a portable and looks more like a small
suitcase than a radio. At just 220 x 110 x
100mm, it is roughly comparable in size to
an average mantel radio of the time. Most
contemporary portables were much larger
and built into a fabric-covered timber case.
From the 1920s onwards, there was
a market for portable radios that had
a role roughly analogous to contemporary mobile phones, as a form of
portable entertainment. You can see
its intended uses in the illustrations
on the cover of the product booklet
reproduced above.
The 450P model has become a collectors’ item. Although they are reasonably common, they rarely come
up for purchase. My good fortune in
acquiring this example was due to the
break-up of a remarkable radio collection, necessitated by the collector’s
poor health. Sadly, many other collections will likewise soon be broken up
due the ageing demographic of most
radio collectors.
The 450P opens up a bit like a 1940s
fridge. However, there is a larger AWA
mantel radio model 520MY that lays
94
Silicon Chip
genuine claim to the fridge title. Iconic radios generally have a descriptor
and being known as “the fridge” adds
resale value.
But either through ignorance or
commercial motivation, the 450P and
other related models have been described this way too. So the 450P is
often referred to as “the AWA Fridge”.
The booklet shows a model 450P
in cream. The Bakelite case is made
of three moulded pieces: the lid, the
top and the bottom. AWA made all of
these parts in cream, black and brown.
They offered the radio with all pieces the same colour or as a two-toned
version with the top being a different
colour from the rest.
It weighs 1.8kg without batteries, so
it is not too heavy to carry, at least not
compared with contemporary portables. The lid has a restraint that only
Australia’s electronics magazine
allows it to open by 90°, protecting the
hinges from damage from overextension. But it looks odd if the radio is carried while switched on; it switches off
automatically in the closed position.
Other portables of the time had
provision for the lid to slide away,
to leave an unobstructed front panel
during use.
The unit I restored has a replacement carry strap. The original handle,
which is shorter, can be seen on the
cover of the product booklet.
Circuit description
The 450P is a minimalistic 4-valve
superhet radio with a conventional
line-up of battery valves. There is no
RF amplification and only one IF amplifier stage. This minimalism, combined with the mass-produced moulded case, kept the price modest. It resiliconchip.com.au
Circuit diagram for the AWA Radiola 450P portable. It’s a conventional 4-valve superhet set with no RF amplification and
one IF amplifier stage (1T4 pentode) with an intermediate frequency of 455kHz.
Source: www.kevinchant.com/model-numbers-401---500.html
tailed for £20.15s.9d.
The circuit here is reproduced from
Volume VII of the Australian Official
Radio Service Manual (AORSM). V1
(1R5 pentagrid-converter) is the mixer/oscillator, V2 (1T4 pentode) is the
IF amplifier, V3 (1S5 diode-pentode)
provides audio demodulation and preamplification and V4 (3S4 pentode) is
the audio output stage, which operates
in Class-A mode.
The large loop aerial is mounted
inside the set’s lid, behind the panel
holding the station logging card. Interestingly, the electrical connections to
the loop are made via the lid hinges.
One wonders how reliable that would
have been. Tuning is via a full-size dual-gang tuning capacitor (which only
just fits in the case) that ranges from
12pF to 450pF.
The oscillator employs a tuned cirsiliconchip.com.au
cuit based around transformer L2/L3
(which has a tuned primary), fixed capacitors C4 & C5 and tuning gang variable capacitor C6. The transformer primary is coupled to the second control
grid (labelled “OG”) of the 1R5, while
the secondary winding is connected to
the screen grids (“SG”) and DC-biased
by the HT supply, decoupled by resistor R3 and capacitor C10.
As the tuned signal from the aerial is
fed to the main control grid pin (“G”),
this is mixed with the oscillator signal and the result appears at the anode/plate (“P”). The gain of this stage
is regulated by AGC fed through the
aerial coil and resistor R2 (6.3MW). The
resulting 455kHz signal passes to the
IF amplifier, V2, via the first IF transformer, L4/L5.
After further amplification, the signal then passes through the second
Australia’s electronics magazine
IF transformer L6/L7 and is fed to the
diode within the 1S5 envelope for demodulation. Capacitor C13 removes
the IF signal and the audio is then
fed to 1MW volume control potentiometer R4. The signal at its wiper is
AC-coupled by capacitor C14 to the
grid of the 1S5 pentode, for further
amplification.
The audio signal at its plate is then
AC-coupled via another capacitor,
C17, to the grid of the 3S4 pentode
output valve, operating in Class-A.
Unlike the more common 3V4 valve,
it is designed to operate reasonably
efficiently from the 67.5V B battery.
Power switch S1 is a spring-leaf type
which is actuated by a metal pushrod.
This protrudes into the opened case
by 5mm, immediately behind the lidlocking catch. The switch’s construction achieves two beneficial outcomes.
December 2018 95
The B battery holder is located at upper left and the two A batteries on the right. This model was designed with a 3S4
pentode valve for the audio output stage, but due to its scarcity at the time, many models used a 1S4 instead.
Firstly, it serves as a double-pole
switch to separately switch each battery. This is necessary because the HT
battery does not connect directly to
ground but instead, to 800W resistor
R9, which provides grid bias for the
3S4 (around -7V). The switch’s second function is to provide a spring
release for the lid. When the catch is
released, the lid pops up and the radio switches on.
Battery life
Most of the power consumed by
this set is in the Class-A output stage
based around the 3S4 output valve.
That includes 5mA from the HT supply (more than half the 8mA total) and
100mA from the A battery (out of a total of 250mA).
As it’s portable, the unit uses relatively small batteries. Fortunately, the
low HT current means that the expensive B battery has a reasonable life.
According to the Service Instructions in the manual, the B battery
would last four times longer than the
A battery. Advertising for the radio
claimed that the batteries would last
for months of casual use.
Restoration
Despite looking cluttered, most of
the components are more accessible
than in many larger sets. The only difficult component to access is the 1R5
valve (V1), which is tightly boxed in
by the B battery tray.
In their service notes, AWA provided the following procedure for chassis removal:
“Remove the back lid and withdraw
The front of the chassis is adorned by just the 3.5-inch speaker and tuning knob, with a tuning range of 540kHz-1600kHz.
The volume control protrudes at lower left of the chassis.
96
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
The lid functions as an automatic on/off switch and the loop aerial antenna is taped to a wooden insert which screws onto
the inside of the lid. The radio is typically shown standing upright, but here it is horizontal, with the volume knob at left,
and the tuning knob on the right.
the batteries from their compartments.
Open the front lid and pull the knobs
straight off their spindles.
Remove the four mounting screws
from the front panel and withdraw the
chassis from the cabinet. Care should
be taken when removing the chassis
that the plunger operating the ON/
OFF switch does not fall out and become lost.”
I first powered up the radio using
bench power supplies and the radio
was utterly mute. It intermittently
drew between 1-5mA from the HT
supply, with the filament current varying between 100-150mA at 1.4V. The
AWA manual states that the HT current should be 8mA and by summing
the valve data, the total filament current should be 250mA.
Cleaning the oxidised valve pins restored the filament current to 250mA
but the HT drain remained at 5mA and
the radio was still completely silent.
The modest HT current at least
meant that the HT filter electrolytic capacitor C16 was still serviceable (a Tecnico 20µF 200VW in a white cardboard
sleeve, mounted above the chassis).
Jiggling the valves (something that I
did almost subconsciously) increased
the HT current to 10mA but the radio
remained silent.
Most capacitors in this radio are
MSP types, colloquially described as
“melted chocolate”. They are notorious for having cracked cases, resulting
in no contact between the axial leads
and the capacitor foils.
In this radio, all the capacitors
looked to be in excellent condition
and indeed none needed replacing. A
The underside of the chassis is primarily populated by the resistors and larger capacitors. The MSP capacitors, which
surprisingly still worked in this set, are coated liquorice-black and marked with “MSP” and their capacitance value. The
leaf-spring power switch can be seen at the bottom centre.
siliconchip.com.au
Australia’s electronics magazine
December 2018 97
handy feature of the MSP capacitors
is that the capacitance value is clearly
visible, as it is moulded into the case.
Editor’s note: MSP stood for Manufacturers Special Products, a division
of AWA which made a very large range
of radio hardware items; tuning gangs,
all sorts of switches, loudspeakers
and significantly, those “chocolate”
capacitors.
While the majority of MSP devices
have stood the tests of time, the capacitors are generally cracked and have
very low insulation resistance; that is,
if they work at all. That this set had
MSP capacitors which were OK is surprising indeed.
So why was the radio silent? The
most common reason for this is an
open-circuit output transformer primary winding because the fine wire
is highly prone to corrosion and going open circuit.
I was dreading this because the
small transformer was going to be a
challenge to replace. Fortunately, I
measured almost the full HT voltage
at pin 2 of the 3S4 (the anode), indicating an intact output transformer
primary.
I used an old-fashioned analog resistance meter to check the continuity
of the secondary of the output transformer, which gave a reading of around
1W, as expected. Significantly, there
was no crackle from the speaker as
I made contact with the meter leads.
Close inspection showed that one fly
lead to the speaker voice-coil was corroded and open-circuit.
There was battery-leakage corrosion close by on the metalwork, so the
speaker was collateral damage.
I hoped that I could fix this without replacing the 3½-inch speaker as
it was unlikely I would find an exact
replacement and would have to make
some changes to accommodate a different speaker.
Fortunately, I was able to temporarily solder a new fly lead to the voice
coil and the speaker then crackled
encouragingly when tested with the
analog resistance meter.
The replacement lead was fed
through a hole in the speaker cone
and soldered to the small tail of the
voice coil wire emanating from the
felt centre cap (see the two photographs above).
This restored the audio section.
Feeding audio input from a CD player
to the 3S4 grid produced surprisingly
98
Silicon Chip
A lead was fed through a hole in the speaker and soldered to the voice coil lead
to restore the audio section.
clear audio, so the speaker was working very well.
This repair will do until I can find
a suitable replacement, a very light
multi-strand wire which is able to cope
with the vibrations of the speaker cone.
The 3S4 grid bias was -7.0V (textbook perfect) but I still couldn’t tune
in any stations. I then discovered that
a lead from the grid of the 1R5 mixer
valve to the loop aerial was shorted to
ground because the rubber insulation
had failed and bare wire was touching the chassis. A replacement lead
restored the set’s operation but there
was a lot of noise and low sensitivity,
making for unsatisfactory listening.
My next thought was that there was
a dry solder joint, compromising the
signal path. I then prodded various
solder joints with a multimeter probe,
simultaneously checking voltages and
also the mechanical integrity, as I was
listening to see whether there was
any change in the set’s behaviour as
I did so.
Contact with a couple of joints produced a miraculous transformation to
excellent performance but it was not
a dry joint problem. Simply providOperation
Connect high side of generator to:
ing an extra antenna at the front end
(ie, the multimeter leads) was what
made the difference. The antenna effect was better at the plate of the 1R5
than at the grid.
I discussed this puzzling situation
with Ian Batty (my fellow Vintage Radio contributor). Ian took the radio
and confirmed my observations. Serendipitously, Ian resolved the problem
by simply aligning the IF stages (see
table below). With hindsight, I should
have done this myself.
The aligned radio handily produced
the 150mW output that the 3S4 is capable of on local stations. The promotional advertising for the radio
claims “beautiful tone and exceptional range”.
The sound is fine but the “exceptional range” claim is hard to credit,
given the limitations of the bare-bones
circuit and small antenna.
In summary, it is an interesting set,
not so much for its very basic circuit
but for its unusual presentation in that
polished Bakelite case.
Few people would recognise it as
a portable radio, at the time or now,
many decades later.
SC
Tune
generator to:
Tune receiver
dial to:
1
2
3
Adjust for maximum peak output:
L7 (core)
Aerial section of gang (front
portion)
455kHz
540kHz
4
L6 (core)
L5 (core)
L4 (core)
Repeat above adjustments until the maximum output is obtained
5
6
7
Inductively coupled to loop
[A coil of 3-turns of 16-gauge
D.C.C wire about 75mm in diameter
should be connected between
the output terminals of the test
instrument and placed co-axial with
the loop]
600kHz
600kHz
1500kHz
1500kHz
LF oscillator core adjustment (L2)
[rock tuning control back and forth
through the signal]
HF oscillator adjustment (C6)
HF aerial adjustment (C2)
Repeat steps 5-7 until the maximum output is obtained
Alignment steps for the AWA Radiola 450P, from the service manual.
Australia’s electronics magazine
siliconchip.com.au
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
Clipping detector with
onboard/offboard LEDs
I have recently built a stereo amplifier using your SC200 amplifier modules (January-March 2017; siliconchip.
com.au/Series/308) and I am delighted
with it. I have fitted the clipping indicator LED (LED6) on each board. Will
it overload the current limiting resistor if I also connect offboard LEDs via
CON4?
Also, do you have a preamp design
which includes tone controls that will
match the SC200 for low distortion?
(M. G., Guanajuato, Mexico)
• It won't damage anything to connect both onboard and offboard clipping LEDs but there's no guarantee that
both will light up.
They could have quite different forward voltages and the one with the
lowest forward voltage will take most
of the current.
You could fit blue LEDs onboard
and red LEDs off-board. In that case,
the onboard blue LEDs will work
when the offboard LEDs are not connected.
When the offboard LEDs are connected, they will take over and light
up with full brightness but the onboard
LEDs will not light up. That is because
red LEDs have a lower forward voltage
than blue LEDs.
We haven't published preamplifiers with tone controls for some time.
But we are working on a digitally controlled preamp with tone controls,
which we think might be published
early next year.
We also plan to design an analog
preamp with tone controls soon and
it may be published mid next year.
GPS Frequency
Reference question
I am planning on building the
analog/oscillator sections of your
GPS Frequency Reference project but
with a different control system. I will
therefore be making my own PCBs
and firmware. But I am wondering if
there would be any advantage in placing the DACs (or at least just IC1) in
the oven. Surely its analog back-end
would be more stable in a tempera-
ture-controlled environment. (R. S.,
East Malvern, Vic)
• The MCP4922 datasheet suggests
that the DNL and INL parameters of the
DAC do not change much with temperature, so we don't think it would
make much difference.
Since these are resistive string type
DACs, we would not expect temperature to have much effect, given that the
values of all the resistors in the string
will change with temperature by more
or less the same amount.
Tide Clock displays
slightly inaccurate time
I have built the Raspberry Pi Tide
Clock described in the July 2018 issue
(siliconchip.com.au/Article/11142)
and it works well.
As my first Raspberry Pi project (I
have always worked with Microchip
PICs before), I had problems with Python2 (Idle).
The text said that I needed Python2
(Idle) but the NOOBS distribution included Python3 (Idle) and I could not
find how to load Python 2.
GPS-synched Frequency Reference drawing too much current
I have just built the GPS-synched
Frequency Reference (October-November 2018; siliconchip.com.au/
Series/326) using the parts supplied
by Silicon Chip, as well as the Micromite Backpack V2 kit.
The BackPack works fine by itself. On powering up the complete
assembly, the software kept resetting
every couple of seconds.
I monitored the 3.3V line and noticed that it was pulsing from 3.3V
down to about 2V. After removing
the 2.7kW resistor from the base of
Q1, the unit powered up normally.
I separated the 3.3V line on the
Frequency Reference board and fed
the board from a separate 3.3V supply. On my board, the initial current
(when cold) was 500mA, which
siliconchip.com.au
reduced to 270-330mA when the
temperature reached 35°C. This is
too much current for the MCP17003302 (250mA) on the BackPack to
supply.
I replaced this with a REG1117-3.3
(800mA). This fixed the problem and
the project works fine now.
I was able to solder the REG1117 on
to the existing pads for Vin and Vout
and used a short piece of wire to connect the device ground to a ground
point at 10µF capacitor which went
to the input of the MCP1700.
The 1.1kW resistor attached to LK1
on the schematic does not exist on
the PCB. I assume it is only required
if LK1 is open.
Thanks for a great project. (P. U.,
Seven Hills, NSW)
Australia’s electronics magazine
•
It sounds like the gain value of
your transistor Q1 (BC337) is much
higher than the ones we used in our
prototypes and therefore it is drawing more current from the supply.
You could solve this by increasing the value of the 2.7kW resistor,
to say 15kW (depending on the gain
of the transistor). That would reduce
the maximum current drawn by Q1.
But your solution of fitting a higher-current regulator is a good idea
and it means that you now have a
GPS Frequency Reference with a
very powerful oven heater, so it will
get up to temperature faster.
The 1.1kW resistor near LK1 was
removed in the final design, as we
found it was not necessary; this was
noted in the November article.
December 2018 99
I managed to load Python2.7.15,
which produced a stream of errors
when I tried to run the Tide Clock software from the Terminal. Eventually, I
realised that Python2.7.13 was loaded
on the machine and that ran perfectly
from the Terminal.
I have two questions. Firstly, the
peak of the sea level graph does not
quite correspond with the vertical bar
at high/low tide time.
At 17:44, it indicated that high tide
would be at 17:46. Then at 17:46, it
indicated that the tide was still rising
but the text says it is falling. Half an
hour later, the indication is that the
tide is falling.
I was surprised to find that the sinewave is calculated 50 times each minute. I was expecting 49 calculations,
there being 48 half hours in two days.
Is the sinewave misplaced, or is the
vertical bar misplaced, or am I just being too picky?
Secondly, I live on Bribie Island,
Qld. The only BoM site for Bribie Tides
is Bongaree on the Passage (west) side
but I live at Woorim on the surf (east)
side where the tides come 20 minutes
after the Bongaree tides. Is it possible
to add 20 minutes to the tide time before displaying the sinewaves?
100
Silicon Chip
Silicon Chip is a great magazine,
long may it continue. (J. N., Bribie Island, Qld)
• We have heard similar reports from
other people saying that they could
not see Python2 in their Raspberry Pi
menus, but it was installed. It can usually be activated from a command line
console by running “idle”. “idle3” is
the Python3 equivalent.
With regards to the accuracy, we
have effectively rounded all times
to the nearest 15 minutes in the tide
display, hence the discrepancy you
are seeing.
It is quite easy to shift the tide times.
In the file tideParser.py, there are two
identical lines that save the tide times
for display (one for high, one for low).
They look like this:
tide.append(datetime.strptime(
a['data-time-local'][:19],
'%Y-%m-%dT%H:%M:%S'))
change both of them to:
tide.append(datetime.strptime(
a['data-time-local'][:19],
'%Y-%m-%dT%H:%M:%S')
+timedelta(minutes=20))
This will make the tides show 20
minutes later than the data would
Australia’s electronics magazine
otherwise indicate. It effectively hardwires an offset into the retrieved times.
You may also need to delete the
“tideParser.pyc” file and reboot your
Pi to reload the files, for this change to
take effect. That is a compiled version
of the Python file. Deleting it forces use
of the new version.
Finding a driver for a
large “stepper motor”
Dear Silicon Chip staff, I have a large
1.5 horsepower variable speed motor
on my wood lathe.
After about five years of hobby use,
the motor controller “spat its dummy”.
No one has been able to repair the
electronics. I measure 2.3W between
each pair of wires. The rotor is made
from four large rare-earth Neodymium magnets.
Do you have a suitable driver design? The motor will index at 12V. (J.
J., Padstow Heights, NSW)
• That is definitely not a stepper motor – it doesn't have enough poles, for
a start. Most lathes are powered by induction motors and with a 1.5 horsepower rating, that would have been our
first guess, except for your comment
about the rare-earth magnets. It seems
siliconchip.com.au
that for some reason, the manufacturers have decided to use a three-phase
synchronous motor instead.
These are similar to induction motors except that the rotor magnetic field
does not need to be induced, as it is
provided by the permanent magnets.
The driving scheme is essentially
the same but the operating speed is a
little bit higher as there is no “slip”
like there would be in an induction
motor. Low-speed control is likely to
be better with a synchronous motor;
perhaps that is why they decided to
use one.
You could drive it using our Induction Motor Speed Controller (AprilMay 2012, December 2012 & August
2013; siliconchip.com.au/Series/25).
It is available as a kit from Altronics,
Cat K6032.
Using pillow speaker
with Insomnia Killer
Can I use the Jaycar Pillow Speakers
(Cat AS3029) with your Tinnitus/Insomnia Killer design (November 2018;
siliconchip.com.au/Article/11308)?
(C. B., Strathalbyn, SA)
• Yes, you can use that speaker with
siliconchip.com.au
this project. But you will need to avoid
turning the volume too loud as they
have a maximum rating of 0.6W and
the Insomnia Killer can deliver more
power than that.
Running SC480 from a
lower supply voltage
I have a transformer which will
give ±30V supply rails when rectified and filtered, and I would like to
know whether I can run the SC480
amplifier module (January-February
2003; siliconchip.com.au/Series/109)
from this supply. It was originally
designed for ±40V supply rails. Do I
need to make any changes to the circuit? (anon)
• We haven't tested this so we can't
say for sure it would work but in theory, the following changes should allow
the SC480 to run from a ±30V supply:
1. Change 15kW resistor at the base
of Q1 to 11kW.
2. Change 18kW resistor at the collector of Q1 to 8.2kW.
3. Change 6.8kW 0.5W resistor at the
base of Q6 to 3.9kW.
The SC200 (January-March 2017;
siliconchip.com.au/Series/308) is
Australia’s electronics magazine
superior in pretty much every way,
especially in terms of distortion and
power delivery, and it isn't any more
complex if you leave out the optional
clip detector circuitry. We suggest
that anybody thinking about building the SC480 should build the SC200
instead.
Glow plug driver not
necessary
Would you consider producing a
DIY article for a model engine glow
plug driver? Many years ago, I built
such a device as advertised in the ETI
Top Projects (Volume 10) book. Later, I
modified it as per the Circuit & Design
Ideas by Phil Allison.
This seemed like a good idea, whereby it adjusts the current to the glowplug depending on its resistance, ie,
as it changes temperature when the
engine starts.
However, I'm finding that its reaction time is too fast and the current
drops rapidly as soon as the engine
fires, allowing the plug to cool too
soon and the engine doesn't always
continue to run.
Also, I'm not sure if this rapid
December 2018 101
LC Meter calibration to remove parasitic capacitance
I recently build the Wide-Range
Digital LC Meter described in the
June 2018 issue (siliconchip.com.
au/Article/11099).
It appears to function correctly
when measuring capacitors and inductors, showing the expected results. The serial monitor display and
menu features work OK.
But when there is no device connected to the input terminals, the
LCD shows a capacitance reading
of 53.74pF. Why am I getting such
a large residual capacitance reading
with no input leads attached? This
change in current (down and back up
again) is good for the glow plug in the
long term. A slower reaction time and
perhaps a lesser current swing might
be better. The commercial units don't
appear to have this feature.
I know that a commercial unit can
be obtained at a reasonable price, but I
like the idea of a DIY or possibly modifying my existing one.
I note that you published an article
by Ross Tester in the March 2000 issue
of Silicon Chip called “Glow Plug Driver for Powered Models” (siliconchip.
com.au/Article/4361).
It is still being sold as a kit by Oatley Electronics. The advantage of this
setup is that it can be powered from
the same 12V source used for the electric fuel pump and the electric starter
that many modellers now use.
Maybe that is the answer. What
are your thoughts? (T. C., Newcastle, NSW)
• We ran this past Bob Young, who
wrote on radio control and model aircraft for many years in Silicon Chip.
He is of the opinion that since the glow
plug is in use for such a short time
while starting that there is no point
in a special driver circuit.
He has never used one. If you want
to use a glow plug driver anyway, our
March 2000 article with the Oatley kit
seems like a good option.
Replacing Mosfet amp
with Ultra-LD Mk3
I am considering upgrading my old
Mosfet stereo amplifier by replacing
the two amplifier modules with the
Ultra-LD Mk.3 modules as described
102
Silicon Chip
is different to what is shown in Fig.4
on page 39 of the June 2018 issue.
I have changed the 100µH inductor and 1nF capacitors but I get very
similar results. I also tried a different LM311 with the same result. Do
you have any suggestions? (M. R.
Karrinyup, WA)
• According to the serial monitor
report that you sent us, you have
not set the calibrations values for
parasitic capacitance and inductance (the Cp and Lp values are still
zero).
The note on the photo on page
in the July and August 2011 issues
of Silicon Chip (siliconchip.com.au/
Series/286).
My question is regarding the power supply voltage requirements. The
Mosfet amp uses a 300VA transformer
that produces ±51V DC when lightly
loaded.
Would the lower voltage degrade
performance at modest levels, say a
maximum output of about 50W? My
8W speaker system is quite efficient
and does not need very high power
levels to be enjoyed.
I also read in a later edition of the
magazine that it is permissible to run
only one pair of output devices in each
channel. Unfortunately, I cannot remember which edition of the magazine
published the details and it would be
appreciated if you could tell me the
month/year. (T. D., Epping, NSW)
• We expect your supply voltages
will drop a little when loaded. The
modules should work fine at that sort
of voltage and will be able to deliver
more than 50W with very little difference in performance from our published figures.
You can run the amplifier with a
single pair of output devices but we
don’t recommend it at that supply voltage. We specified lower supply rails of
around ±42V to ensure that the load
current is within the capability of a
single pair.
You’re probably remembering the
article which starts on page 32 of the
October 2015 issue. This is for the
Ultra-LD Mk.4 but its design is similar to the Mk.3 and the same principles apply.
We simply omit the outer pair of
Australia’s electronics magazine
39 mentions that these values can
be adjusted.
A value of 53pF sounds about
right pre-calibration (our unit measured around 57pF). The instructions
for calibration start on page 39, and
the specific instructions for calibrating out stray capacitance are on
page 41.
Both of these values default to zero
because each unit will be slightly
different, so we recommend that
constructors follow these calibration
procedures to get maximum accuracy from their Meter.
devices and the associated emitter resistors. Three resistors are changed, to
suit the lower supply voltages.
One resistor value is different in the
Mk.3 version but similar changes can
be made; the 6.2kW resistors would
still be changed to 4.7kW while the
22kW collector resistor for Q8 would
become 16kW.
A simple capacitive
pickup for tachometer
I need a versatile tachometer for general servicing and tuning up of my car.
I think the circuit from the October/
November 2006 issues (LED Tachometer with Dual Displays; siliconchip.
com.au/Series/82) could easily be
modified for my purpose. The only
thing it lacks is an inductive pickup
to trigger the unit.
I want to be able to feed the trigger
input from an inductive pick up from
one of the spark plug leads to avoid
having to play around with trying get
to the engine management wiring, as
it will only be used for servicing. My
car (a 2004 TL Magna) has a distributor and computer, so there is no wasted spark or divide-by-two problem.
I would also like to be able to use it
on single cylinder two-stroke engines
in the same manner.
Have you ever described such an
inductive pick up that could be used
with this project? As I do not need
the LED bar graph display, would it
still work if I omit the LEDs in the
bargraph and just use the 7-segment
display instead?
Finally, I would like to point out that
there is an error in the circuit diagram
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(Fig.3) on page 29 of the October 2006
issue. Q2 and Q3 are labelled on this
diagram as BC337 but shown as PNP
transistors.
The parts list shows Q2 and Q3 as
BC557, which I assume is the correct
part. (P. C., Woodcroft, SA)
• You can make a capacitive type
pickup by winding several turns of
wire around the spark plug lead. One
end should be left disconnected and
the other end connected to the highlevel input of the tachometer.
Alternatively, a larger area pickup
siliconchip.com.au
could be made from sheet metal that
wraps around the spark plug lead.
Then connect this to the high-level
input on the tachometer.
You may need to experiment with
the number of turns or metal area required to trigger the tachometer. The
pickup may affect the voltage that is
delivered to the spark plug and this
method will only work if the spark
voltage is positive with respect to vehicle chassis.
You may also need to modify the
Tachometer input circuit, The 47nF
Australia’s electronics magazine
capacitors at the input may need to
be reduced in value, perhaps to less
than 100pF.
The 10kW and 100kW resistors may
also need to be higher in value, eg,
470kW each. The 2.2µF capacitor will
need to be a non-polarised type.
If your spark polarity is negative-going, it will not trigger the tachometer.
There is no need to include LEDs133 if these are not required. The circuit
will work fine without them.
You are right, Q2 and Q3 should be
BC557 types.
SC
December 2018 103
Coming up in Silicon Chip
3D printing – the latest technology
David Maddison takes an in-depth look at all the latest 3D printing technology,
including many amazing commercial applications, including building homes!
AM/FM/DAB+ Radio with Touchscreen Interface
This is a world-first; a DIY world radio which can receive AM, FM and DAB+
broadcasts. It's controlled using a Micromite Explore 100 module with a 5-inch
colour touchscreen and has an on-board amplifier for driving stereo speakers, a
headphone output, line outputs and provision for external AM and VHF antennas.
Advertising Index
Altronics............................. FLYER
Anritsu....................................... 33
Blamey Saunders hears............ 36
Dave Thompson...................... 103
Digi-Key Electronics.................... 3
Emona Instruments................. IBC
Freetronics.................................. 9
Isolated Serial Link
Hare & Forbes....................... OBC
This small and easy-to-build board provides optical isolation for two devices
communicating over a 3.3V or 5V level serial link. It's great for connecting a
micro module with a mains or battery power supply to a PC, to prevent power
glitches and avoiding damage to the PC from a fault in the connected module.
Jaycar............................ IFC,49-56
Primer on stepper motors
Stepper motors are used in a variety of electromechanical devices, including
hard disk drives, CD/DVD/Blu-ray players, laser cutters and 2D/3D printers.
Jim Rowe details how stepper motors work, and how you use them.
The BWD 216A valve+transistor power supply
BWD was a major Australian electronics manufacturer from 1955 to the 1980s.
This power supply, released in the mid 1970s, truly showed off their prowess.
It could deliver 0-400V with an adjustable current limit of 0-200mA, and had a
separate isolated 0-250V output at up to 50mA.
Note: these features are planned or are in preparation and should appear
within the next few issues of Silicon Chip.
The January 2019 issue is due on sale in newsagents by Monday, December 31st. Expect postal delivery of subscription copies in Australia between
December 28th and January 11th.
Keith Rippon Kit Assembly...... 103
LD Electronics......................... 103
LEACH Co Ltd........................... 41
LEDsales................................. 103
Microchip Technology............. 7,93
Mouser Electronics.................... 23
Ocean Controls......................... 10
PCBcart................................... 37
PCB Designs........................... 103
PicoKit....................................... 43
Premier Batteries...................... 73
Rohde & Schwarz........................ 5
SC Vintage Radio DVD............ 101
Silicon Chip Xmas Tree.......... 100
Silicon Chip Shop...............82-83
Silicon Chip Subscriptions....... 57
Notes & Errata
Tinnitus & Insomnia Killer, November 2018: on page 65, the text refers to Fig.2
as showing the pink noise output but it is actually shown in Fig.3.
LED Tachometer, October & November 2006: in the circuit diagram (Fig.3), on
page 29 of the October issue, Q2 and Q3 should be labelled as BC557 types, not
BC337.
Switchmode Power Supplies..... 31
The Loudspeaker Kit.com........... 6
Tricom Components.................... 8
Tronixlabs................................ 103
Vintage Radio Repairs............ 103
Wagner Electronics................... 11
WARNING!
SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such
projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring
should be carried out according to the instructions in the articles.
When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains
AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high
voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages
should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine.
Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the
infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any
liability for projects which are used in such a way as to infringe relevant government regulations and by-laws.
Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the
Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable.
104
Silicon Chip
Australia’s electronics magazine
siliconchip.com.au
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