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.

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?

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.

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.