This is only a preview of the July 2011 issue of Silicon Chip. You can view 30 of the 104 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Items relevant to "Ultra-LD Mk.3 200W Amplifier Module":
Items relevant to "A Portable Lightning Detector":
Items relevant to "Rudder Position Indicator For Power Boats":
Items relevant to "A Look At Amplifier Stability & Compensation":
Items relevant to "Build A Voice-Activated Relay (VOX)":
Purchase a printed copy of this issue for $10.00. |
This little device could save your life . . .
You don’t want to be caught in
a storm, especially if you are
on a sports field, out boating,
bushwalking or working in the
open, on the farm or anywhere
else where there is minimum
shelter. If there is even a risk
of a storm, take this Lightning
Detector with you before
venturing outdoors.
Lightning
Detector
W
hile most of us love the wide open spaces,
they are definitely not the place to be if a thunderstorm is on the way. If there is a lightning
strike nearby you could be in big danger of death or injury.
And you don’t have to be hit directly – induction can kill
you and so can the voltage gradient across the ground in
the vicinity of a lightning strike.
Our Lightning Detector can warn you of an approaching lightning storm and provides valuable time to take
shelter safely indoors. And even if you’re not outdoors it
can give you warning to disconnect vulnerable electrical
appliances from the 230VAC mains supply. It provides
audible and visual indication to warn of approaching
thunderstorms.
Lightning damage to electronic appliances
Many people do not realise how vulnerable electronic
equipment can be in a thunderstorm, even if it is not close
by. Service organisations report a big surge in repair jobs
42 Silicon Chip
by John Clarke
after storms and just about all of this could be avoided
simply by switching off and removing power plugs from
the wall socket.
Those appliances especially at risk include microwave
ovens, TV sets, satellite receivers, mains powered computers (especially those also connected to the phone lines via
a modem), washing machines and dryers.
They should not be just switched off at the power point
but the mains plug should be removed from the socket.
TV antenna and satellite dish connections should be disconnected too. Many ovens incorporate electronic timers
and power to these can be switched off at the “fuse” box.
Apart from mains-powered computers, devices that
are particularly prone to damage are fax machines and
cordless telephone base stations. It is the fact that they are
connected to both the 230VAC mains and the telephone
wiring that provides a double whammy. During a big
thunderstorm they should be disconnected both from the
phone line and the mains power.
siliconchip.com.au
Of course, it is well known that any
phones (apart from mobiles and cordless models) should not be used during
a thunderstorm.
So what to do?
S1
+3V
1.5V POWER
SUPPLY
(Q1, LED3 & 4)
LED2
BATTERY
3V POWER
SUPPLY
(2 x AA
CELLS OR
PLUGPACK
INPUT)
CONDITION
To get a warning of imminent thunINDICATOR
1.5V
derstorms, you need the SILICON CHIP
Lightning Detector. It is a pocket-sized
SINGLE CHIP
PULSE
unit that provides visual indication usOSCILLATOR
AMPLIFIER
AM RADIO
EXTENDER
(IC3)
(Q2)
ing a flashing LED and sounds an audible
(IC1)
(IC2, D3)
PIEZO
TRANSDUCER
tone whenever lightning occurs in your COIL
area. The greater the number of lightning
DETECT
strikes, the more LED flashes and audible
LED1
VR1
tone bursts are produced.
SENSITIVITY
For portable use it is powered with
two alkaline AA cells, Battery life should Fig.1: the block diagram of the Lightning Detector. The early part looks
be at least 1000 hours. For indoor use, similar to a radio receiver – which of course it is – but this radio receiver
you can use a 6V-12V DC supply, such picks up just one thing: the RF pulse from a lightning strike within range.
as a plugpack. One resistor needs to be
chosen according to the DC supply voltage. When the exThe pulse extender produces a 200ms pulse and this
ternal power supply is connected to the jack the socket, the lights the “detect” LED1. The pulse extender is necessary
AA cells are automatically disconnected from the circuit. because the lightning strike pulses are too short in duration
The principle of operation is based on detection of the to be noticed as a flash from the LED.
broad-spectrum electromagnetic emissions produced by
IC3 is an oscillator that runs for 200ms each time the
lightning strikes. This is readily detected by a simple AM pulse extender produces a low signal and the resulting 4kHz
(amplitude modulation) radio receiver.
tone burst drives the piezo transducer which is resonant
If you’ve ever been anywhere near an electrical storm at that frequency.
with an AM radio turned on, you’ll have heard the crashes
(static) of lightning strikes. Very large strikes can be heard Circuit details
from a considerable distance away.
The full circuit is shown in Fig.2. As mentioned, IC1 is
We use a single AM radio IC which comprises a RF the TA7642 AM radio chip while CMOS 555 timers are used
(radio frequency) amplifier, detector and AGC (automatic for the pulse extender IC2 and for 4kHz oscillator, IC3. The
gain control). This was originally available in 1984 from circuit is powered from 3V but it will operate down to 2V.
Ferranti Semiconductors as the ZN414Z but replaced by
A 1.5V regulated supply powers IC1 while the amplifier,
the MK484, now also obsolete.
pulse extender (IC2) and the oscillator (IC3) are driven
We have used the modern equivalent, the TA7642. It from the 3V supply.
operates from a 1.2 to 1.6V supply and covers from 150kHz
While most of the circuit is powered from the 3V supto 3MHz. This includes the normal AM radio broadcast ply rail, IC1 needs to be operated at between 1.2 and 1.6V.
band (530kHz to 1.6MHz) but for our purposes, we are To provide for this we use a voltage regulator comprising
not concerned with listening to broadcast radio stations. transistor Q1 plus infrared LED3 & LED4. These develop
We simply monitor the whole spectrum covered by the a forward voltage of approximately 1V each which is reAM radio chip.
markably constant over a wide range of current. Tests of
several infrared LEDs from different manufacturers showed
Block diagram
that the forward voltage is around 1.09V at 1.6mA current
The general arrangement of the Lightning Detector is dropping to 0.945V at 160A, ie, a current range of 10:1.
shown in the block diagram of Fig.1. IC1 receives signals
Stacking two infrared LEDs in series provides a reasonfrom a pickup coil. In an AM radio this pickup coil would ably stable 2V reference. The LEDs are fed via a 2.2kΩ
normally be tuned to a particular frequency using a vari- resistor from the 3V supply and the 2V reference drives
able tuning capacitor.
the base of transistor Q1. This acts as a current buffer to
We want to monitor a wide frequency range and so the supply IC1 with about 1.4V. This varies from 1.46V with a
coil is left un-tuned. IC1’s output signal is noise bursts 3V supply down to 1.287V with a 2V supply.
from lightning.
IC1 is connected to the 1.4V
Output from IC1 is typically
supply via the 470Ω AGC resistor
15mV with a tuned coil but is
at its output pin. A 100nF decouparound 2mV with the un-tuned
ling capacitor at the output sets
• Portable
coil. This signal is amplified using
the high frequency rolloff to 4kHz.
• Battery or external power supply
transistor Q2 and a sensitivity conOne end of the pickup coil L1 is
trol sets the level applied to the fol• Visual and audible lightning indication connected to the high impedance
lowing pulse extender comprising
(around 3MΩ) input of IC1 while
• Sensitivity control
IC2 and diode D3. When lightning
the other end is grounded via a
• Battery condition indicator
is detected, a noise-burst triggers
100nF ceramic capacitor. There
• Reverse supply protection
the pulse extender.
is no parallel capacitor across
Features
siliconchip.com.au
July 2011 43
+3V
2.2k
C
B
A
K
E
LED3
(IR)
220k
D3 1N4148
VR1
10k
LIN
470
LED4
(IR)
10nF
8
7
C
Q2
BC549C
B
TA7642
L1
I
100nF
100nF
IC1
G
E
CER.
1
10k
CER.
470nF
180k
22nF
6
5
1k
CON1
A
22
A
LED1
K
POWER
S1
PIEZO
TRANSDUCER
1
1nF
OSCILLATOR
A
BATTERY
LED2
3V BATTERY
(2 x AA CELLS)
LIGHTNING DETECTOR
K
100k
K
10 F
16V
A
SC
5
+3V
180
D2
1N4004
B
R1: FOR 12V INPUT -- 470 0.5W
FOR 9V INPUT -- 330 0.5W
FOR 6V INPUT -- 120 0.5W
L1: STANDARD BROADCAST BAND
FERRITE ROD ANTENNA
2011
3
IC3
7555
A
DETECT
K
ZD1
3.9V
1W
8
4
2
PULSE EXTENDER
D1 1N4148
R1
7
K
AM RECEIVER
12V DC
INPUT
IC2
7555
2
100k
180k
4
3
6
O
100nF
K
A
SENSITIVITY
K
100k
100nF
100k
2.2k
100k
100nF
A
100nF
470k
Q1
BC547
10 F
16V
220k
E
BC547, BC549C,
BC559
Q3
BC559
B
C
E
TA7642
LEDS
IN4148
A
K
1N4004
A
K
K
A
C
O
I
GND
Fig.2: the three main functional areas of the circuit diagram are labelled the same as block diagram to enable you to trace
the circuit operation through. As mentioned in the text, resistor R1 needs to selected depending on the DC power supply
you use – it can handle anything from 6 to 12V. The battery supply is nominally 3V but it will operate down to 2V.
L1. This means that the coil is un-tuned and will have a fully at 2V and we are inclined to assume that this IC does
broadband response. Bias for the input of IC1 comes from also operate at 2V.
a 100kΩ resistor connected to its output.
Make sure you do not use bipolar 555 timers such as the
IC1’s output is AC-coupled to the following common LM555CN or the TL555CP as these typically require 4.5V
emitter amplifier, Q2. This has its emitter resistor bypassed or more for operation.
with a 22nF capacitor to provide a gain of about 50 for freIC2 is the pulse extender which is set up as a monostable
quencies above about 723Hz. Q2’s collector load comprises timer. Before triggering occurs, pin 3 is close to 0V and the
the 10kΩ potentiometer VR1 and a 2.2kΩ resistor. VR1 is 470nF capacitor is held discharged at about 0.6V above 0V
the sensitivity control.
by diode D3. Pin 2 is held at 45% of the 3V supply, ie, at
IC2 and IC3 are CMOS 555 timers and most manufacturers +1.35V, using the 220kΩ and 180kΩ voltage divider resistors.
of these devices state that their version will operate down
Triggering occurs when the noise signal fed to pin 2 pulls
to 2V or less. These include the Intersil ICM7555IPA, Texas it below +1V. This sets pin 3 high and diode D3 is then
Instruments TLC555CP, ST Microelectronics TS555CN and
reverse biased. The 470nF capacitor then begins to charge
National Semiconductor LMC555CN. The NXP (found- via the 470kΩ resistor. During this time, LED1 is lit (driven
ed by Philips) ICfrom pin 3) When
M7555CN guaranthe voltage across
tees operation at 3V
the 470nF capacitor
over full automo- Supply voltage:
reaches 2/3 of the
3V (2 x AA cells) [will operate down to 2V]
tive temperatures.
supply voltage, pin
Plugpack: 6 to 12VDC at 30mA
However, perfor- Current Consumption:
3 goes low and the
Battery operation 1.5mA at 3V, 1mA at 2V,
mance graphs show
470nF capacitor is
DC plugpack operation 17mA at 12V
operation with a Battery life:
discharged via diTypically 1000h with Alkaline cells
2V supply at –55° IC1 supply:
Typically 1.46V with 3V supply, 1.28V with 2V supply ode D3.
C, 25°C and 125°C. Battery voltage indication:
This is an unconDown to 2V
Also samples of the Strike indication duration:
ventional monosta200ms
NXP ICM7555CN Transducer frequency drive: 4kHz
ble timer arrangeoperate success- Frequency detection band:
ment. Normally pin
150kHz to 3MHz
Specifications
44 Silicon Chip
siliconchip.com.au
2.2k
220k
LED1
VR1
A K
S1
A K
IC3
7555
470nF
10 F
1nF
220k
180k
100k
10k
100k
2.2k
PIEZO
Q2
D2
CABLE
TIES
22nF
10 F
Q3
100nF
100nF
180
470k
D3
4148
100nF
IC2
7555
1k
L1
10190210
R OT CETED G NI NT H GIL
10nF
LED2
180k
ZD1
D1
4148
22
R1*
100k
100k
100k
100nF
CON1
470
LED4 LED3
A
100nF
(-)
100nF
IC1
+
Q1
A
* R1: SEE TEXT (DEPENDS ON VOLTAGE IN)
+
–
TO BATTERY
HOLDER
TERMINALS
Fig.3: everything (except the batteries) mounts on a single-side PCB.
The component layout is shown above and, with the same-size photo
at right, is self-explanatory. At right is Fig.4, the drilling guide for the
end panel. There is no labelling on this panel; all controls are labelled
on the front panel. Millimetre dimensions are the hole diameter
required at each position.
7, the discharge, would be connected to pin 6 and would
discharge the 470nF capacitor instead of using diode D3.
Using D3 to discharge the capacitor frees pin 7 to perform
another task. Because it can sink (pull down) to 0V, it is suitable for use as a reset control for the following oscillator, IC3.
IC3 is connected in astable (free-running) mode, running
at about 4kHzm to drive the piezo transducer. It is held
in the reset condition, with its pin 4 pulled low by pin 7
(discharge) of IC2, when IC2 is not timing.
Power supply
As already mentioned, the Lightning Detector is powered
from two AA-cells or a low voltage plugpack supply. When
running from the AA cells, current flows via the closed
contact in the power connector (CON1) and through the 22Ω
resistor to the 0V supply. This resistor is included to prevent
excess current if the cells are inserted back-to-front. When
the cells are correctly inserted, the 22Ω resistor produces
a minimal voltage drop (normally less than 33mV and less
than 100mV with the detect LED lit).
When running from a DC suppy, the AA cells are disconnected via CON1 (as noted above) and the incoming
supply is regulated down to 3.9V using zener diode ZD1
and resistor R1. The value of this resistor depends on the
DC supply voltage – anywhere from 6V to 12V will be suitable, with resistor values of 120Ω (6V), 330Ω (9V) or 470Ω
(12V). The negative supply connects to the circuit ground
siliconchip.com.au
End Panel Drill Guide
Switch
5mm
LED
3mm
LED
3mm
Pot
7mm
via the 22Ω resistor.
Diode D1 reduces the 3.9V zener voltage supply to about
3.3V. We could have used 3.3V zener diode on its own without D1. However, we want to be able to run the circuit from
two AA cells that provide a 3V supply. If a 3.3V zener diode
were used, the cells would be discharged via the zener diode.
So by including diode D1, current is prevented from flowing through the zener diode. The zener voltage is increased
from 3.3V to 3.9V to compensate for the 0.6V diode drop.
D1 also blocks reverse voltage to the circuit should the 12V
supply be connected with reversed polarity. With reverse
polarity, zener diode ZD1 is forward biased and clamps the
voltage to no more than -0.6V below the 0V supply. D1 stops
current flowing through the circuit backwards.
Battery indication
When the power is first switched on, LED2 provides indication of the battery condition. LED2 is driven via PNP
transistor Q3 and its base is initially tied to 0V via the 10F
capacitor. With the supply at 3V, Q3’s emitter is at about
0.6V and the LED is driven at maximum brightness. That is
with about 2.4V (3V-0.6V) across the LED and 180Ω resistor.
Assuming a LED forward voltage of 1.8V, this produces a
current of about 3mA.
At a lower supply voltage, the initial LED current is less
and it will be dimmer. With a 2V supply, LED2 will be barely
alight, indicating that the batteries should be replaced.
July 2011 45
Parts List – Lightning Detector
1 PCB coded 04107111, 65 x 86mm
1 remote control case 135 x 70 x 24mm (Jaycar HB5610
or equivalent)
1 panel label 50 x 114mm
1 miniature PC mount SPDT toggle switch (Altronics
S1421 or equivalent) (S1)
1 10k log potentiometer, 9mm square, PCB mount (VR1)
1 knob to suit potentiometer
1 switched 2.5mm PCB mount DC socket (CON1)
2 AA Alkaline cells
2 DIP8 IC sockets (optional)
1 tuning coil with ferrite rod (Jaycar LF-1020)
1 piezo transducer (Jaycar AB-3440, Altronics S 6140)
2 6mm spacers
2 M2.5 x 12mm screws
4 6mm self-tapping screws
2 100mm cable ties
6 PC stakes
1 50mm length of red light gauge hookup wire
1 50mm length of black light gauge hookup wire
Semiconductors
1 TA7642 single chip AM radio (IC1) (Wiltronics
X-TA7642)
2 7555 CMOS 555 timers (ICM7555IPA, TLC555CP,
TS555CN, LMC555CN or ICM7555CN) (IC2,IC3)
2 3mm high intensity red LEDs (LED1,LED2)
2 5mm IR LEDs (LED3,LED4)
1 BC547 NPN transistor (Q1)
1 BC549C NPN transistor (Q2)
1 BC559 PNP transistor (Q3)
1 3.9V 1W zener diode (ZD1)
2 1N4148 switching diodes (D1,D3)
1 1N4004 diode (D2)
Capacitors
2 10F 16V PC electrolytic
1 470nF MKT polyester
4 100nF MKT polyester
2 100nF ceramic
1 22nF MKT polyester
1 10nF MKT polyester
1 1nF MKT polyester
Resistors (0.25W, 1%)
1 470k
2 220k 2 180k
5 100k 1 10k
2 2.2k
1 1k
1 470
1 180
1 22
1 of 120, 330 or 470 0.5W (R1 – see text)
Whatever the supply, LED2 only lights momentarily and
as the 10F capacitor begins to charge via the 100kΩ resistor, it dims and eventually goes out. The 220kΩ resistor
across the 10F capacitor prevents the capacitor charging
to any more than 2/3rds the supply. This provides a faster
discharge of the capacitor when the supply is switched off.
The 220 resistor is also used to discharge the capacitor
when the supply is off so it is ready to flash the LED when
power is reapplied.
Construction
The Lightning Detector uses a PCB measuring 65 x 86mm
46 Silicon Chip
Here’s how the PCB fits
inside the case. The top
corners need to be shaped
to fit the case mounting
pillars but otherwise it’s
a simple drop-in fit,
secured by four selftapping screws . The
two AA batteries
which power the
unit fit under
the moulding at
the bottom.
and coded 04107111. The PCB and components are housed
in a plastic case measuring 135 x 70 x 24mm.
The PC board is designed to mount onto the integral
mounting bushes within the box. Make sure the front edge
of the PC board is shaped to the correct outline so it fits
properly. It can be filed to shape if necessary using the PCB
outline shape as a guide.
Begin by checking the PCB for breaks in tracks or shorts
between tracks or pads. Fix any defects, if necessary. Check
the hole sizes for the PCB mounting holes and for the cable
ties. These are 3mm in diameter.
You can then insert the resistors and use the resistor
colour code table to select each value and check each one
with a digital multimeter. Then install the diodes; they
must be mounted with the orientation as shown. Install
the six PC stakes.
IC2 & IC3 can be mounted on sockets or directly soldered
to the PCB. When installing sockets and ICs, take care to
orient them correctly – as indicated by the notch at one end.
Capacitors can be mounted now. The electrolytic types
must be oriented with the shown polarity. Make sure these
capacitors are placed on the PCB so their height above the
surface is no more than 12.5mm, otherwise the lid of the
case will not fit correctly.
Note that while provision is made for a capacitor across
the L1 coil, as mentioned earlier one is not used in this
circuit.
It is included so that you can experiment with the radio IC
by placing a tuning capacitor between the two PC stakes for
the L1 coil and placing a fixed value (if required) capacitor
to pad out the capacitor range. This will allow the reception
of radio broadcast stations.
Audio signal is available at the VR1 wiper. A coupling
siliconchip.com.au
plastic transducer tabs. Alternatively, two nuts can be used.
Follow the wiring diagram to make the connections from
the piezo transducer and battery terminals to the PC stakes
on the PCB.
Next, install the battery clips into the battery compartment. The two connected terminals are placed on the right
hand side (as you look at the rear of the case with the compartment at the bottom). The spring terminal is placed to
the top and raised section to the bottom. For the left side,
insert the separate terminals with the spring terminal placed
at the lower edge and the raised section to the top.
On the compartment inside bend the two individual
terminals to the outside of the compartment. You may need
to stretch the contact springs so that the AA cells are held
securely between the contacts.
Looking end-on shows the two controls and two LEDs
The PCB is secured to the base of the case using four M3
which mount on the end panel. Fig.5 (below right) is the
x 6mm screws that screw into the integral mounting bushes
same-size front panel artwork which can be photocopied
in the box. Before fitting them in place, drill out the small
or downloaded and printed, then glued in place.
front panel for the LEDs, potentiometer and switch. A drill
guide is available and is provided with the
capacitor (say 100nF or so) is required
front panel label. This can be used as a guide
to connect this signal to an external
Sensitivity
Detect
Power
as to the drill hole positions.
amplifier.
The panel label for this project can eiMount IC1 and the transistors taking
ther be photocopied (without infringing
care to place each in its correct place.
copyright) – see fig.5 – or for best results,
If you happen to be using a Ferranti
it can be downloaded from the SILICON CHIP
ZN414Z from your IC collection for
website (www.siliconchip.com.au). Go to
IC1 note that the GND and Out pins
the downloads section and select the month
are reversed compared to the TA7642.
and year of publication.
You would have to place the IC in the
When downloaded, print it onto paper,
PCB oriented 180° to that shown on
sticky-backed photo paper or onto plastic
the overlay.
film. For protection and long life, paper
An MK484 has the same pin out as
labels should be covered with either selfthe TA7642. The TA7642 has a greater
adhesive clear film or (as we normally do)
sensitivity in the lightning detector aphot laminated (laminators and sleeves are
plication compared to the MK484 and
very cheap these days and give a tough
so given the choice, we recommend
protective layer!).
using the TA7642. We did not try a
DC
If printing on clear plastic film (overhead
ZN414Z since this is not available.
Input
projector film) you can print the label as a
The potentiometer (VR1) and the
+
mirror image so that the ink is behind the
PCB-mounted switch S1 can now be
film when placed onto the panel. Again, this
soldered in.
will give the label maximum protection.
LED1 and LED2 mount horizontally
Once the ink is dry, cut the label to size.
but at a height of 6mm above the board
The paper or plastic film is glued to the
surface. Bend their leads 90° at 7mm
panel using an even smear of neutral-cure
back from the base of the LEDs, making
silicone. For plastic film, if you are gluing
sure the anode lead is to the left.
it to a black coloured panel, use coloured
L1 is a standard broadcast band coil
silicone such as grey or white so the label
pre-wound onto a small ferrite rod.
can be seen against the black.
There are actually two coils on the rod
A hole in the panel is required directly
but only one is used.
Using your multimeter, find the coil that has the greatest above the piezo transducer. This can be first drilled in the
plastic lid and then once the panel label is affixed, cut the
resistance. With our prototype, the main winding measured
about 11, while the separate antenna winding measured hole out using a sharp hobby knife.
A small piece of dark fabric or loudspeaker foam
2. Connect the coil with the highest resistance to the PC
(scrounged from an old pair of headphones) can be used to
stakes.
The ferrite rod is secured to the PCB using a pair of small cover the piezo transducer. Also a black bezel over the panel
hole can improve the finish of the unit. These are secured
cable ties.
The piezo transducer is mounted using two 6mm long with a smear of neutral cure silicone. Our bezel came from
standoffs and 12mm long M2.5 screws. The screws are the plastic dress plate that sits behind the nut of a Jaycar
inserted from the underside of the PCB, pass through the PS-0192 stereo 6.35mm jack socket.
Additionally, a cut out is required for access to the DC
spacers and tap into the piezo mounting tabs. If you are using
a different piezo transducer that has larger mounting holes socket. A rat-tail file can be used to make this hole in the lid.
A suitable belt clip for the remote control box is available
in the tabs, M3 screws could be used instead to tap into the
SILICON
CHIP
siliconchip.com.au
.
July 2011 47
RESISTOR COLOUR CODES
No. Value
4-Band Code (1%)
1 470kΩ
yellow purple yellow brown
2 220kΩ
red red yellow brown
2 180kΩ
brown grey yellow brown
5 100kΩ
brown black yellow brown
1
10kΩ
brown black orange brown
2
2.2kΩ
red red red brown
1
1kΩ
brown black red brown
1
470Ω
yellow purple brown brown
1
180Ω
brown grey brown brown
2
22Ω
red red black brown
One of the following (R1):
1
470Ω
yellow purple brown brown
1
330Ω
orange orange brown brown
1
120Ω
brown red brown brown
1
1
1
1
1
1
1
1
1
1
1
1
1
Capacitor Codes
5-Band Code (1%)
yellow purple black orange brown
red red black orange brown
brown grey black orange brown
brown black black orange brown
brown black black red brown
red red black brown brown
brown black black brown brown
yellow purple black black brown
brown grey black black brown
red red black gold brown
Value F Value IEC Code EIA Code
470nF 0.47F
470n
474
100nF 0.1F
100n
104
22nF 0.022F
22n
223
10nF
0.01F
10n
103
1nF
0.001F
1n
102
the 22Ω resistor should be about 33mV
with a 3V supply or less with a lower
voltage supply.
Check supply to IC1 at the emitter
of Q1. This should be 1.46V with a 3V
supply dropping to 1.287V with a 2V
yellow purple black black brown
supply.
orange orange black black brown
Adjust the sensitivity control fully
brown red black black brown
clockwise or back off if any indication
persists. Test the Lightning Detector as
from Altronics. The catalog number is H0349. (Contact a fluorescent light is being switched on. The switching on
www.altronics.com.au).
of conventional fluorescent tubes will cause the Lightning
Detector to give a LED detect and tone indication with
Testing
each starter attempt to light the tube. Compact fluorescent
Testing can be done with two AA cells or a DC supply. tubes tend to be indicated with a single flash and tone as
Apply power and check that the power LED momentar- the tube lights rapidly.
ily lights when the Lightning Dectector is switched on.
The sensitivity control is included to prevent the
Check the supply voltage by measuring across diode D2. Lightning Detector from producing an indication when
This should be around 3V but may differ depending on there is no lightning. The control is adjusted clockwise
the state of the cells or the tolerance of the 3.9V zener for maximum sensitivity to lightning but not so far as to
SC
diode when a DC power supply is used. Voltage across give false detection.
What to Do in a Storm
The best idea is to avoid getting caught outside in an electrical
storm but sometimes, the best laid plans of mice and men. . . etc.
How far away is the lightning?
Watch for a flash of lightning. Then count or read off your watch
the number of seconds until you hear the first crash of thunder (or
crack if it is close!). Divide the number of seconds by three and you
have a rough distance away that the lightning has struck. Anything
less than 1km (ie, 3s) should be regarded as getting very dangerous.
If you cannot get to shelter?
If you are caught outside during an electrical storm, avoid
conductors of electricity such as water, trees, poles, golf clubs,
umbrellas and metal fences.
If possible, keep away from open spaces (eg, the middle of
a sports field) where you will be taller than the surroundings
and definitely do not shelter under a tree. Crouch down, keeping your feet close together and wait out the storm. Groups of
people should be spread out several metres apart.
It is also a good idea to cover your ears with your hands to
avoid hearing damage due to the noise of a close lightning strike.
If possible, take refuge inside a vehicle or building. If inside a
vehicle, close the windows and avoid touching the metal of the
vehicle. Make yourself less of a target by lying down (eg on the
back seat). Keep the vehicle away from trees or tall objects that
may fall over in the storm. Avoid fallen power lines.
Inside a building, keep windows and doors closed and keep
48 Silicon Chip
away from windows, doors and fireplaces. Before the storm,
unplug electrical appliances that may be susceptible to lightning
damage. These include fax machines, telephones, microwave
ovens, televisions and computers. To be doubly safe, unplug
any computer communications devices from phone lines or
cables (don’t forget routers etc).
Avoid using electrical appliances and telephones until the
storm has well and truly passed. (However, you can use a
mobile phone if you have to – eg, to call for help).
Avoid touching earthed fittings such as water taps, sinks,
appliances and so on.
If you are on a boat, keep low, dry, and away from metal
conductors. Always check with the Bureau of Meteorology for
storm forecasts before going out on a boat. In this way you
could avoid boating in a storm. If you are a boat owner, make
sure the boat is fitted with lightning protection that directs
lightning safely to the water. This will help protect the occupants
should they be caught out in a storm and also help protect the
boat when left moored.
And if someone near you is struck by lightning?
Avoid the temptation to rush in and help – time is of the
essence but there’s no point in two people being struck!
As soon as it is safe to do so (ie, the danger has passed),
commence standard A-B-C resuscitation. Check their response,
clear the airway, and if necessary proceed with CPR.
What? You don’t know CPR? Learn it today!
siliconchip.com.au
|