Are there X-rays from light globes?

Some enthusiasts on the Internet have raised issues about harmful emissions of Gamma and X-rays from certain mixtures of ionised gases. In particular, one experimenter suggests that the nitrogen rich mixture of gases found within common incandescent globes might emit such rays in substantial quantities.

Do you see this as a legitimate concern or simply uninformed hysteria? If it is a concern, what kind of position would the magazine take on such matters? (M. M., via email).

We doubt whether X-rays and Gamma rays could be emitted from ordinary incandescent lamps – you need a very high voltage to get X-rays in a discharge tube – that is why large TV CRTs DO emit X-rays. By the same reasoning, a plasma display could also emit low level X-rays.

However, halogen lamps and most gas discharge lamps do emit UV and this can be at quite high levels. So much so that the high intensity lighting in some sports arenas can give bad sunburn after a few hours! We also regard halogen desk lamps as potentially dangerous because they are positioned so close to the user’s eyes.

Theremin is mute

I bought a Theremin kit from Dick Smith Electronics (described in August 2000). I have built the PC board but I cannot get my Theremin to produce a tone. I have checked very carefully that I have not created any short-circuits with my soldering. I am at the stage of tuning the voltage between the transformer coils and pin 1 of IC2 to 4.3V but I cannot get a reading on the multimeter between these two parts. I would appreciate any advice you can give me. (S. M., via email).

If you have a power supply which can deliver 9 to 12VDC, try the Theremin operation with this or use a 9V battery. This will check whether the plugpack you are using is working.

Other tests would include checking the various supply rails in the circuit with respect to the ground. Check for about 6V at pin 6 of IC3 and pin 8 of IC2. IC1 does not have a power supply pin (as it is a collection of transistors) but the various pins should have voltages on them. The drains of Q1 to Q3 should have about 5V.

Testing the rest of the circuit without an oscilloscope could be difficult. You could disconnect the 1kΩ and 100Ω supply resistors for the separate oscillators, so that you have only one oscillator operating at a time. Bring an AM broadcast band radio close to the Theremin. Check that you can hear a whistle which is varied when you tweak the relevant oscillator coil.

This will indicate whether or not each oscillator is working.

Apart from that, check your soldering very carefully for missed joints or solder splashes. Most project faults are due to soldering problems.

Running the white LED torch at 1.2V

I constructed the White LED Torch, described in the December 2000 issue, from a Dick Smith Kit. It works brilliantly. I have two questions. Is it possible to run the LED at 20mA+ from a 1.2V rechargeable cell with minor changes to the circuit? This would make the unit more useful on long trips away from services. Secondly, can it run, with modification, from a 3V source, allowing incorporation into combined radio/torch setups? (H. B., via email).

The White LED Torch can be operated from 1.2V by shorting out resistor R1. This will increase the current drive to the LED. Essentially the current is limited by the DC resistance of inductor L1 since this determines the saturation current.

We do not know the characteristics of the commercially wound inductor used in the Dick Smith kit. Winding your own using the Xenon tube transformer former will enable you to increase the LED current when using a 1.2V supply. You would need to use 250 turns of 0.25mm enamelled copper wire (rather than the 0.16mm wire specified) on the bare former.

You could run the torch from 3V but R1 should be increased to 4.7Ω.

TV pattern generator has no colour I have recently made up the Colour TV Generator kit described in the June & July 1997 issues of SILICON CHIP. It performs perfectly at the video output but I can’t get colour when using the modulator output. The modulator provided in the kit is a "Wittis" MM0002V-A12, replacing the original "Astec" suggested in the 1997 article. The circuit was modified to include a 5.1V zener diode, leaving the 180Ω resistor in circuit. Flexible leads connect the modulator to the main board. On connecting the modulator on Channel 1 to a TV set, the bars present well (without colour) and all the patterns (except the Red Raster) are well defined with a mid-range setting of VR2. Varying the input level to the modulator and shorting out the 470μF coupling capacitor will not produce colour. Have I missed some later technical advice to correct the problem? I am tempted to change the modulator. (G. P., via email). Some modulators require a resistor between ground and the input to set up the internal DC conditions. You can use a value of 1kΩ. We recall that the Wittis type requires this resistance.

Increased brightness for Video Doctor

I recently built your Video Doctor kit from the April 2001 issue and I am very pleased with it. However, as an experiment I attempted to make a copy of my video of Star Wars, to see how effective the kit is at removing the protection. It worked well, except that it was apparent that the picture from the copied video was not as bright as the original. This is the same, with or without the Video Doctor. Unprotected videos are not affected in this way. Is this a function of the copy protection and if so, can I do anything about it? (D. M., via email),

The brightness level of the output from the Dr Video unit can be adjusted but it does involve a bit of ‘fiddling’ and component substitution on the PC board. You can try replacing one or both of diodes D4-D5 with germanium diodes or ‘hot carrier’ diodes, which will give a lower voltage drop and hence lower the black level given to the video in the input DC restorer. This should do the trick but if it makes the picture darker rather than lighter, try adding a germanium diode in series with D4 and D5 instead.

Calibrating the LED Bargraph Ammeter

Can you please help me with the LED Bargraph Ammeter described in the January 1999 issue. When calibrating it on my car with VR1 fully anticlockwise I am able to adjust VR2 until the green and yellow LEDs are lit. But when the parking lights are turned on to adjust VR1, the LEDs go off the board, not towards the centre. Also, when the engine is started, nearly all LEDs light and twinkle. Pin 6 of IC3 is showing +4.4V but all other voltages seem OK. (J. C., via email).

Check that you have -5V at pin 4 of IC1. The +4.4V at pin 6 of IC3 is normal since the 555 is oscillating and this is the average voltage, as measured with a multimeter.

Also check the wiring between battery (-) and the cable earth. Perhaps these connections are transposed. You can increase the filtering to stop the LEDs from flickering by changing the 0.1μF capacitor between pins 1 & 2 of IC1a to a 1μF bipolar (non polarised) electrolytic. Note that VR2 may need readjusting after you have set VR1.

Driving fuel injectors from the hot chip

I have the Investment Technologies Hotchip miniboard as reviewed in the February 2000 issue of SILICON CHIP. I have written a program for it that enables the A-D converter and follows voltages until a predetermined (and variable) point and then switches port B (only one pin is currently used) on and off very fast; ie, pulses of between 4V and 5V at 20mA of current.

I have designed this program to read the voltages from a typical 0-5V MAP sensor as found in most turbocharged cars (mine included). What I have done is set the chip up so that it pulses port B on and off in the manner of a fuel injector. I would now like to run a fuel injector off these pulses.

What sort of relay system do I need to run one injector solely from the hotchip and switched 12V? Do you know of a relay that can be switched by only 20mA @ 4.5V yet handle 400mA @ 14.4V to drive the injector? Will a relay switch fast enough and be able to handle the continuous on and off cycles and yet remain reliable? (R. W., via email).

No relay is suitable. Injectors are usually driven by Darlington transistors designed for just that purpose. Some later model cars are also using Mosfet or IGBTs (insulated gate bipolar transistors).

We suggest you try using the IRLZ44NS/L logic level power Mosfet from International Rectifier. You can get it from Farnells (Cat 637-488). Phone 1 300 361 005.

When is a watt a WATT? Are there many different ways of measuring power consumption for compliance labels in various countries of the world? Being involved with hifi equipment, I often see completely illogical and obviously plain wrong power consumption figures on amplifiers. I have numerous examples but one to hand is a giant 26.5kg Sony N77ES power amplifier which is rated to consume 490W for the UK model, 510W for the multi-voltage model, 950VA for the Canadian model and 380W for the US model. These are the various country models, all rated the same output of course, as listed in the service manual. The amplifier delivers in excess of 200W continuous into 8Ω per channel, 270W+ into 4Ω per channel and over 540W as a bridged mono amp. So, is a watt a WATT or not? Is power conserved or do these amplifiers actually manufacture their own power? Only kidding. As Pauline would say, "Please Explain". (J. R., via email). We have no idea why the various country ratings are different. In fact, at maximum power into 8Ω the amplifier would consume in excess of 700W and over 900W at maximum power in bridge mode, assuming normal power supply and class-B efficiency. However, this would virtually never occur in normal use so perhaps the various countries derate the power consumption. The 950VA rating for Canada probably also recognises power factor as part of the equation. Given maximum power output, the Canadian rating looks the most realistic (and conservative). We actually reviewed that amplifier in February 1988. Given the exaggerated PMPO ratings of many ghetto blasters, we think they MUST manufacture their own power out of thin air.

Revised software for speed alarm

I purchased your speed alarm kit from the November 1999 issue and am about to build it but I noticed on the SILICON CHIP website software page that there is a revised program for the microcontroller. I purchased the kit from Jaycar and I need to know which version the chip may be and what the revision actually does. Can you help? (S. G., via email).

The original software for the Speed Alarm (first version) allowed speeds on the alarm and speedo function up to 155km/h. The newer software (second version) called speed255.ASM allowed the alarm and speedometer function to reach 255km/h. Both versions are suitable for road use.

The second version was produced for those wanting to use it for racing purposes. The software in your speed alarm is probably the first version. You can check which version you have by checking how far the speed alarm settings can go. If they can go higher than 155km/h then it is the second version.

Water cure for noisy power pole

At times I was getting atrocious TV reception of Channel 2 due to power pole interference – sometimes the set was reduced to a blue screen. The interference seems to mess up the TV and VCR AGC function as well as the picture signal.

I traced it to a particular power pole using a transistor radio as a direction finder. I thought it was a bad insulator or cross-arm. That was fine but what could I do about it other than fruitlessly complain to the power authority? Anyway I planted some flowers at the base of this pole and I found that the constant watering made the interference sharply less. Clearly it is something to do with the pole having a bad earth. So, problem solved.

I have the flowers there to explain to the neighbours my need to water my power pole. If TV interference climbs I water the power pole and the interference disappears!

Others in similar trouble may be interested in this. (R. D., Salisbury Heights, SA).

We assume that you have very low rainfall and that the ground is very dry. However, you should know that constantly watering around the base of the pole may promote rot and make the pole unsafe. In Sydney, the relevant authorities discourage planting around poles for that reason. Do you have the option of UHF reception?

(Editor’s note: upon receiving our reply, our correspondent phoned to say that the offending power pole was made of reinforced concrete).

On making an electric wheelchair

Could you please tell me if you think a 12V motor/gearbox from a windscreen wiper would be powerful enough (using two) to drive a wheelchair that I intend to build. It would be lightweight and used mainly around the kitchen. The commercial ones are too large, heavy and expensive.

Also would a computer joystick (modified) be robust enough to handle the voltage and current required to steer it, etc? (S. G., via email).

12V windscreen wiper motors will do the job but the joystick will not handle the current. You will have to do the switching/speed/direction via a switchmode H-bridge circuit. Have a look at the Railpower train controller circuit we published in October 1999 as the basis for the switching circuit – it has been used in electric wheelchairs before.

12V version of battery charger I refer to the Automatic Battery Charger published in the June 1996 issue. I wish to build this as a dedicated 12V charger, without the 6V or 24V options. I assume that I won’t need IC1a, IC1b, IC1c, Q5, Q6, Q7, LED5, LED6, LED7 and associated components. However, I still need to obtain a stable 2V on pin 2 of IC2 for the 12V battery function. I have a few questions relating to this. Can I obtain the 2V for pin 2 of IC2 via a voltage divider from the reference voltage (5V) at pin 14? Can I do away with Q1, D1, D7 and S2? Can I simplify the RC network around D2 and IC2, and is D2 needed? Is the battery sense line down to IC1a able to be used to turn off IC2 when no battery is connected, as per the original circuit? I realise that one approach is to simply leave it the way it is, but I don’t want to have to use the override switch when the 12V battery is very low in voltage. With my changes, I will connect the leads to the 12V battery, turn the charger on and forget it. Any assistance will be much appreciated. (G. D., via email). To obtain the 2V for pin 2 of IC2 use a 2.2kΩ to ground and 3.3kΩ to the 5V reference. Yes, you can do away with Q1, D1, D7, and S2. To simplify the RC network around D2 and IC2, you need to connect the 100kΩ and 4.7kΩ resistors to ground where they previously connected to the anode of D2. D2 can be omitted. The battery sense line down to IC1a cannot be used to turn off IC2 as the Mosfet and driver circuit is disconnected.

Stereo preamplifier lacks bass

I just built the magnetic cartridge version of the stereo preamplifier based on the LM833 (see SILICON CHIP, April 1994). To my surprise the circuit is acting like a pure amplifier with no RIAA compensation.

When playing through the tuner inputs on my amplifier, the sound is all treble, but if I turn my treble right down and bass right up, it sounds about right. Conversely, if I plug into the cartridge input, the frequency balance is about right although it overloads easily.

I have looked carefully at the way I put the kit together and I can’t see anything wrong. In any case, both channels exhibit the same behaviour, which surely eliminates a bad soldering job, mixed up components, or a faulty component. Is there a possible explanation that I have overlooked? (G. B., via email).

It seems extremely likely that you have not put the RIAA feedback components in or you have some bad solder joints. Check that R1 (16kΩ), R2 (200kΩ), C1 (.0047μF) and C2 (.015μF) are all in place and properly soldered.

Using a retired video monitor

What about a means of utilising spare (usually 14-inch) computer monitors for video cameras – using those little ‘cameras-on-a-PCB’ things that sell for around $100 for B&W. Some of the better ones seem to have a reasonable degree of resolution when displayed through a good TV.

I know you could "play" them through a video card but that’s like using the Roller to round up the sheep. (J. L., via email).

Unless you are talking about a pre-VGA monitor with a composite video input, it won’t work because it will not be compatible with the sync signals from typical NTSC or PAL cameras. We published a project featuring a miniature camera and old monitor in the June 1995 issue and revisited the subject in the October 2000 issue.

500W amplifier for subwoofer use

I’m considering building the 500W amplifier, described in the August, September & October 1997 issues of SILICON CHIP, for use in a subwoofer application that needs to be flat down to at least 10Hz. The specs printed in the relevant issues give a frequency response between 20Hz and 20kHz but no farther.

Can you tell me the -3dB point at the bottom end, or better still, provide a frequency plot? (N. N., via email).

The frequency response is quoted as 20Hz to 20kHz at the -0.3dB points so you can expect that the response at 10Hz is less than -1dB down. By the way, 10Hz is not audible (it can be felt at high levels) and there is no subwoofer that goes to 10Hz – most don’t even go below 25Hz.

Capacitance in house wiring Perhaps you can shed some light on house wiring voltages and leakage with regard to neon indicator lights in switch plates and power points. I have a double power point with inbuilt neons, and with nothing plugged into it and the switches off, the neons glow very faintly (only visible in the dark). I assume it cannot be leakage due to faulty wiring, as the neons are integral to the power point. Secondly, I have two neons connected to switches in one room that turn off lights in another room. If both switches are off, the neon glows very faintly but if the one nearest the light (a fluoro) is on and the other one near the neon is off, the neon does not glow at all. A similar problem occurred with the other neon when the other light was installed. The switch and neon went in first, then the wiring and light a week or so later. Once again, this neon glowed very faintly in the dark with the switch off. Once the light (also a fluoro) was wired up, this neon does not glow faintly when the switch is off. The wiring to both is correct, with neutrals and earths going back to the switchboard. I assume it is the same problem as the power point neons. I also saw this problem at my father’s house. He had an external light with a neon at the switch. No problems, until he had an extension added and an electrician removed the light but temporarily left the wiring with connectors on it. Then this neon also glowed faintly in the dark with the switch off. This house had been fully rewired a few years before. In all of the above, with the switches on the neon glows fully as you would expect. Any idea as to why? (J. B., via email). Without devoting the time to fully analyse your letter, the explanation for your observations is almost certainly due to the capacitance of the wiring. If you have a capacitance meter, try measuring the capacitance of a 10m length of mains cable. You will be surprised.

Coil-based electric fence wanted

I seem to recall you did a project for a home-made electric fence based on an automotive coil. I am trying to find this kit and have checked all my local electronics shops to no avail, so was wondering if you could give me details of this kit please. (M. P., via email).

We published the coil-based electric fence kit in July 1995. Kits are no longer available but an almost identical kit, using the same PC board, is available for the Jacob’s Ladder, published in September 1995, from Jaycar. Cat KC-5191.

We can supply the back issues for $7.70 including postage.

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 Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable.