Are laser
beams visible?
A friend of mine is building a full-scale model Dalek from the
good ol’ Dr Who series and wants to make a laser beam shoot out of its gun. I
have looked around and found a couple of lasers such as the LM3 on the Oatley
Electronics webpage (http://www.oatleyelectronics.com/lasers.html). The blurb for this unit states: "This module
emits an orange/red beam which is more visible and brighter than the 650-670nm
modules. Consists of a visible laser diode, diode housing, APC (automatic power
control circuit) driver and collimation lens, all factory assembled in one small
module".
Does this mean that you can actually see a beam of light coming
out of the laser module? If so, how far would this beam travel? (C. G., via
email).
In clear conditions,
a laser beam or any light beam for that matter, cannot be seen travelling
through air although you can obviously see where it lands on a surface. However,
if the beam passes through dust, mist, smoke, etc, it will be visible. Perhaps
you could use a fog machine to create the special effects that you desire.
Depending on factors such as the lens, laser power and
wavelength, the beam may travel many kilometres.
IR train detector
needs pulsed signal
I have made several attempts to construct an IR train detector
for my model train. I have found circuits in my model rail books dating back 10
years. I have also bought kits, some too expensive to duplicate and others where
the parts are not clearly marked or the provider will not tell me the component
values.
The circuit I have sent to you is the easiest one I have found
but the LED is on all the time when I apply 12V filtered DC. I have tried
reducing the value of R1 and have also tried D1 and Q1 from different sources to
no avail.
Could you help me out here? I am a novice electronics user,
although I have had previous success with other circuits. (G. J., via
email).
We are unable to
assist with troubleshooting circuits not published by us. We have not published
an IR train detector but would suggest that you could base one on the IR Light
Beam relay in the December 1991 issue or the Infrared Sentry in the April 1999
issue. Both circuits use a pulsed IR signal – any other approach is futile.
Fixing Japanese radio frequency coverage
I want to purchase a Japanese car audio system that has FM from
76.0-90.0MHz and AM from 522-1629kHz. However, I want to change both the AM and
FM coverage to our Australian frequency range.
The receiver has a digital screen interface but is not digital
radio – just analog. There is a the link to the Japanese receiver at:
(1) http://www.honda.co.jp/navigation/insight/audio.html
(2) http://www.honda.co.jp/ACCESS/gathers/audio/wx252m/index.html
Is this possible to change? If so, what is the procedure for
this? Would a firmware update be possible if I can find one? (Z. I., via
email).
A firmware update
would probably be the complete solution but we have no idea where you would get
it. If you can find the OEM manufacturer, you might have a better chance.
By the way, it should not be necessary to change the AM
coverage unless it doesn’t step in 9kHz. The FM de-emphasis will probably be
75ms instead of the Australian standard 50ms and would probably require a
capacitor change.
Cheap LCD screen for reversing camera
I wish to completely remove the LCD screen from some of those
cheap 5-inch portable DVD players and turn them into usable screens for use with
reversing cameras for cars. Has any reader done this or can you advise on how to
do this? Maybe you could do an article on a conversion. (S. V., via
email).
It may not be
possible to do this. There may be no point inside the unit to which you could
connect an analog video signal since all processing, from the DVD to the LCD
screen, is probably in the digital domain.
Diode substitution
in power supply
I am building a 400V valve power supply following the article
in the July 2004 issue. When I went to order some BYV26G diodes from RS
Components I found that they have been discontinued. What would be a suitable
alternative?
Seeing that I am only building a 400V version, could I use the
BYV26E diode (1000 PIV versus 1400 PIV for BYV26G)? Alternatively, could I use
two of them in series to achieve the required voltage handling? (S. G., via
email).
We expect that the
BYV26E would be fine for the 400V version of the supply. Alternatively, the
BY448 (Farnell stock No. 995-150) may be suitable, although we haven’t tried
it.
Air-bag aid for
epileptic patient
I do some work for TAD (Technical Aid for the Disabled). One of
our clients has epilepsy and keeps falling over and has received some nasty
injuries.
We have been thinking about an airbag approach; ie, like in a
car. Every-one thinks there is not enough time. My estimate is that we would
need to detect the fall and take action within about 150ms. Airbags take about
50ms to inflate. I was thinking about an MEMs sensor.
Have any of your people any ideas or experience in this area?
(J. J., via email)
Airbags certainly go
off very quickly, as detailed in our article on the subject in the February 1994
issue. Typically they take just 30ms to inflate but they also deflate very
quickly, at around 100ms.
However, there would be real problems in adapting automotive
air-bag technology because they activate so explosively and can cause injury to
anyone in too close proximity.
Then again, how would you predict how the patient was going to
fall and how would you decide how the airbag(s) should be positioned and
activated to cushion the fall? Detecting the fall would also be very difficult
since it could be in any direction and may happen very quickly or in "slow
motion". Again, if the fall is slow, the airbag might be activated before it
could be of use.
Maybe some sort of padded suit would be a better proposition.
In fact, maybe airbag technology could be used to pressurise the suit when a
fall was detected. It is an interesting idea but we do not have any experience
in this area.
Digital slave
flash trigger
I am currently assembling the Digital Slave Flash Trigger
(SILICON CHIP, July 2003). One small
problem was the hot running of Q2. As it turned out, it is essential to turn one
of the switches to the "on" position to prevent full voltage being present on
the output of IC2b.
The circuit works well (it is still on the bench without its
casing) with a single flash but is erratic when I put the camera on "anti-red
eye". In that setting, it puts out many flashes, six I guess, and then two main
flashes and the reaction of the unit becomes very unpredictable and sometimes I
get the impression it is still counting on from the previous set of flashes.
Either that or the inconsistency is caused by the photodiode
not being sensitive enough and just picking up a signal here and there. (C. B.,
via email).
From your
description of the way your Slave Flash Trigger is "misbehaving", we suspect
this may be due to it being uncased. This will reduce the effective output pulse
level from the photodiode, because of the somewhat higher ambient light
level.
We suggest that you fit the board assembly in the box and also
place the lid on temporarily. Then try its operation again and it’s likely that
it will behave more predictably.
Note that it is necessary to have at least one of the DIP
switches (D1-D5) set, because otherwise the counter (IC1) cannot count pulses
and trigger the slave flash. If your camera provides, say, six brief pre-flashes
and two main flashes in "anti red-eye" mode, you’d need to set the switches to
count eight pulses, so the slave slash is triggered only on the second main
flash from the camera.
Remote sensor
for the bilge sniffer
I wish to build the Bilge Sniffer (SILICON
CHIP, September 2005) but would prefer to have the hydrocarbon gas sensor
mounted remotely in the underfloor area of a ski boat. The PC board would be up
on the instrument panel for waterproofing and monitoring/control purposes.
Is there is any reason why the sensor cannot be mounted
remotely from the PC board? (D. B., via email).
The sensor can be
mounted remotely. You can use a twin shielded cable to do this, with one side
for the 5V supply and other for the signal.
Command control is now obsolete
Back in January 1998 you did a Command Control project for
model trains. Are the parts still available and if so, where can I obtain them?
Also, did you revisit that project with a revamp? (R. M., McLaren Vale,
SA).
The ZN409CE used in
the decoder modules would now be very difficult to obtain. In any case, you
would probably be better off considering a changeover to a DCC system as the
modules are now relatively cheap.
Electrical storm damage to a computer
I’m writing with an enquiry about my computer and the
possibility that faulty electrical wiring behind the power point into which is
was plugged into, contributed to it being damaged in an electrical storm.
There was no surge protector on my computer – that is my fault
and I was fully prepared to get a new computer, because I did not have a
protector on it. But then I found that the other computer in the house was also
plugged in during the storm and was not damaged.
I am now wondering if my computer was damaged because it was
plugged into a faulty socket. If this is the case, I feel it might be the
landlord’s responsibility to get me a new computer.
When you move a cable that’s plugged into the power point, the
power flickers on and off. When I plugged a powerboard into it, I did notice
that the light indicating the power supply was flickering. I hope you can give
me some advice. (K. W., via email).
Even if your power
point is faulty, it is not likely to have caused damage to your computer. It is
possible to have perfectly sound wiring and have just one appliance damaged
during a storm. Computers are particularly vulnerable because they are usually
hooked up to the power and also to the phone system via a modem which means they
get a double-whammy.
Surge protectors can help but the only sure way to ensure no
damage occurs during a thunderstorm is to completely disconnect your computer;
ie, don’t just switch it off at the wall – unplug it as well.
The same caution applies to other mains-powered appliances.
Lightning can kill any appliance, regardless of how much surge protection may be
in place.
If you have contents insurance, you may be able to claim for
the damage.
Head-up display
for a car
Would you have any plans for a Heads-Up Display for vehicles?
It would seem to be only a small modification to your digital speedo project a
while ago, just reversed.
It would be an excellent safety modification kit that would
appeal to many people. (D. W., via email).
We do not have any
plans – it would be a huge job, including the installation of a display
projection unit.
SCART interface
cable wanted
I am hoping that you can advise me on a way to feed a signal
from my new set-top box to my VCR.
My new Samsung Digital Set-top Box/DVD player has a SCART jack
and a SCART/RGB cable to enable connection to a VCR. My reasonably new Panasonic
VCR (NV-SJ 230) does not have RGB jacks. It has only a coax jack and two (white
and yellow from memory) jacks.
Is there such a thing as a SCART/COAX converter cable? If so,
who makes it? If not, can you think of a way to feed a signal from the set-top
box into the VCR? (P. H., via email).
Pin 19 of the SCART
socket on your STB is composite video out. You can purchase SCART to RCA socket
adaptors to let you connect your VCR. For example, Dick Smith Electronics have a
SCART multi-adaptor at $23.96; Cat. L-0023. If your VCR has S-video inputs, you
can also get a SCART to S-video cable.
Powering five 20W amplifier kits
I have five 20W amplifier modules and would like to know what
is the best and cheapest way to power all five if they are all going to be in
the one box. The kit instructions refer to the SC480’s power supply and it
mentions that it is only powerful enough to power two amplifier kits. There is a
100W amplifier (the SC480) that is powered by the same supply. Would I be able
to use it to power my five 20W amplifiers? (D. B., via email).
We assume your
amplifiers are based on the 20W Schoolies Amplifier, as described in December
2004. You’ll need a 150VA transformer or better, to power all five modules.
The SC480 power supply is not up to the job, as a higher total
current is required at the lower supply rails required by these amplifiers.
However, a suitable power supply can be constructed from readily available
parts.
A pair of 10,000μF 50V capacitors (Altronics R-5601) and a 10A metal bridge
rectifier (Altronics Z-0088) would do the job. The capacitors can be
conveniently installed on the K-3010 mounting board, while the bridge rectifier
should be bolted to a metal panel for cooling. Use heavy-duty hook-up wire to
connect it all together and keep the wires to the rectifier as short as
possible.
Troubleshooting The Ignition System
I successfully built the breakerless ignition project
(SILICON CHIP, June 1988) and used it in two different cars
until eight years ago when I bought a car with electronic ignition. I have now
installed it in an older car running with points and after running for two
weeks, it won’t go any more.
I am aware of the latest High Energy Ignition system but I’d
like to fix the old one, especially because I have some spare MC3334P ICs in
stock. Basically, I need some advice how to troubleshoot it.
I have replaced the IC without success. I am doing the
troubleshooting on the bench (I use a spare coil, single spark plug, power
supply, etc). When I rotate the distributor by hand, the spark plug will not
fire. It will fire once when I connect the power, then nothing when turning by
hand.
The Darlington checks OK with a multimeter but I don’t know how
to troubleshoot the IC. Can you please help? (G. D., Morwell,
Vic).
First, with power applied, short the base
of Q1 to GND. This turns off Q1 and should produce a spark each time you do it.
If this is OK, the Darlington and output zeners are good. If this test is not
OK, check the voltage at Q1’s base – it should be about 1.3V. If it’s 0V, IC1 is
internally shorted.
Now try pulling the junction of the 470kΩ ; 22kΩ resistors to GND. This
should cause a spark each time you do it. If OK, then Q2 may be
suspect.
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Problem With Studio 350 Amplifiers
I purchased two Studio 350 amplifier kits from Jaycar. I have
years of experience in building kits and I thought I'd give this one a go.
Unfortunately, after constructing one of the amplifier kits, I found that it
didn’t work.
Upon powering up, I observed that the output was not even close
to 0V. It was almost full negative rail voltage. Before assembling the kit, I
made sure that I had adjusted VR1 and VR2 to their midpoints so they wouldn’t
cause any trouble later on.
I turned the power off and checked that I had not connected
anything the wrong way. After a long observation, I found no faults. I
re-powered the circuit and the same thing happened. Even adjusting VR1 and VR2
made no difference. The 6.8kΩ resistor got so hot it burnt.
I used a signal generator to try to locate any shorts and
couldn’t find any. I wasn’t sure if I had made a mistake so I thought I would
build the other kit to see if it would do the same thing. I assembled the second
amplifier, checking every resistor value just in case. I left out D4 and D5
because they’re not really needed and I only put in Q10 and Q11 just to make it
easier to test.
I predicted that the second amplifier would do the same as the
first because I am pretty confident in my construction ability. Not to my
surprise, this second amplifier went full negative rail on the output as
well.
I had two other people help me fault-find, who are a bit more
experienced at fault-finding than me. At first look at the circuit, I got the
comment that the resistor values around Q4, Q5 and Q6 were rather low values but
I was told it probably doesn’t really matter.
We disconnected the 22kΩ feedback resistor and grounded it and
then we grounded the two 100Ω resistors on the base of Q8 and Q9. We powered the
circuit up to only 20V on the rails because I was worried that if we put the
power up too full, it would burn the 6.8kΩ resistor again.
Q2, Q3 and Q1 all seemed to work OK. We then checked Q4 and Q5
and they seemed to be saturated. Q6 was also drawing a lot of current. We
rewired the circuit back to normal and re-powered the circuit to 20V again. We
experimented with increasing the value of the 100Ω resistor connected between
the 70V rail and D3. This started to have an effect on the output.
VR2 did not seem to have any effect. We ended up changing the
100Ω resistor between VR2 and Q7's base to 470Ω. This then had some sort of
desired effect. I then had an output offset of about 2V which could not be
improved using VR1. Then I fed a sinewave from a signal generator to the input
and observed the output. VR2 had an effect in removing crossover distortion.
The output signal was about 40V peak-peak. This was with the
470Ω 10W resistors in place of the fuses, so I expected the output voltage to be
a bit low because of voltage drop across the resistors. The sinewave on the
output was slightly distorted.
Since then, I have not bothered with any further experimenting.
Could you please give me some feedback on how you might think I could resolve
this problem? (M. T., via email).
What possessed you to start making
wholesale changes to the circuit? You should not be making any changes. Hundreds
of this amplifier have been built without any problems and we have used this
general circuit configuration for over 20 years. In other words, if your
amplifier does not work, assume that you have a fault, not a design problem!
The fact that Q4 & Q5 are saturating indicates that the
problem is in the early stages, possibly involving Q2 & Q3. Have you
measured the voltages there? We suspect you might have the wrong transistors
installed for Q1, Q2 & Q3 or possibly they are wrongly connected. Q6 should
not be drawing high current although it might be getting hot. Again, have you
measured the voltages around it?
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Upgrading The 15W Class-A Amplifier
I have just finished your 15W Class-A Amplifier (SILICON CHIP,
(July & August 1998), as sold by Altronics. It sounds great but I would like
to upgrade the output capacitors. Would this be possible? Also I would like to
increase the bass a little. Any ideas on how I could do this? (R. M., via
email).
There are no output capacitors as such, since like most semiconductor power amplifiers, this is a direct-coupled design.
The only capacitor in the output stage is the 150nF unit in the output filter
and this is a metallised polyester type so there is no point in changing it for
something supposedly better. This is still the best-performing amplifier we have
ever described and no design published anywhere else can touch it.
You cannot really improve the bass response since it is already virtually
flat to below 10Hz. Nor can you afford to apply much bass boost since that can
rapidly run the amplifier into overload at quite modest power outputs. If your
system really is bass deficient, you can try placing the speakers closer to the
walls or corners (tends to muddy the sound quality) or upgrade the speakers
themselves.
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Notes & Errata
Mixture Display, Electronic Projects for Cars, Vol.2: the
text on page 46 does not agree with the circuit and PC board component diagram
which shows two red LEDs for rich mixtures and two yellow LEDs for lean
mixtures. Since lean mixtures can damage a motor, the red and yellow LEDs should
be swapped so that red LEDs indicate a lean mixture while yellow LEDs indicate a
rich mixture.
iPOD Charger, February 2006: with some iPOD models (eg, the iPOD Video),
charging will not initiate when connected to the iPOD Charger. The remedy is to
solder a 1kΩ 0.25W resistor between pins 2 and 3 of the USB socket on the iPOD
Charger. In this way, the iPOD will recognise that the iPOD Charger has been
connected. The resistor can be directly soldered to the pins of the USB socket
beneath the PC board.
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