Wire gauge for white LED torch

I’m currently constructing the white LED torch as described in the December 2000 issue of SILICON CHIP. Unfortunately, I am in Perth and none of Dick Smith Electronics, Jaycar or Altronics carry the 0.16mm enamelled copper wire specified for the construction of L1, the 220μH inductor.

I was curious as to whether either 0.125 or 0.2mm wire would be suitable and if so, whether any adjustment would be necessary to the number of turns. (J. L., via email).

The wire gauge is not critical. Use 0.2mm if that’s all you can get.

How to improve Commodore ventilation

I drive a Holden VL Commodore and the ventilation could be a lot better. The heating/cooling/air conditioning fan in the cabin has a four stage switch. (I believe all the VB to VL Commodores have pretty much the same fan and the same switching mechanism). Can you design a circuit that could be connected to the fan to make it run faster? I want it 1.5 times faster on setting 1 and so on. (D. H., via email).

It is possible but it’s not really practical and the fan would be a lot noisier in any case. We’re pretty sure the fan motor will be a permanent magnet type and therefore the speed control is basically just a tapped resistor in series with the motor (it was this speed control which was subject to a recall of the VK Commodore due to a fire hazard!).

So since it is a permanent magnet motor, the only way to make the fan run faster is to increase the input voltage and this can only be done by using a relatively high power step-up inverter.

Using a PC for video editing

As a keen video editor, I need to control my VCR with my PC using the RS-232 port to drive V-LANC or the 5-pin edit control port on VCRs. I hope you have some ideas on how to build such a project. (V. P., via email).

We have not published any article which is relevant to your application but if other readers indicate an interest we shall consider doing a project to suit.

Opto-electronic pickup wanted

Could you please advise on what brand of opto-electronic pickup was used in the opto-electronic version of the High Energy Ignition article on page 58 of the October 2000 edition of SILICON CHIP? And where can I purchase it? (B. G., via email).

We do not know the particular brand of opto sensor. It was requested by a reader who had a sensor with a common ground connection. The circuit can be used with the Crane Cams optoelectronic points replacement unit. These should be available from high performance automotive parts suppliers. Another circuit for this optoelectronic pickup was published in the Circuit Notebook pages of the August 1988 issue.

As an alternative to using a commercial unit, you could use a photo-interrupter from Jaycar (Cat ZD-1901) and make up your own interrupter disk to break the infrared beam.

Protection components for mixture display

I have a mate who runs your bargraph mixture display (SILICON CHIP, November 1995) and he keeps blowing the chips. He tells me there is a fix for it you released. So I offered to install it for him but I need to know if you can help me with a description of the fix? (G. M., via email).

You need to add three components: a 39kΩ resistor in series with pin 5, a 10Ω 0.25W resistor in series with the 12V supply and a 15V 1W zener across the 12V supply after the 10Ω resistor. The 15V zener clips off any spikes on the 12V supply. The details were shown in EFI Tech Special which is available from us for $8.95 including postage.

Substitute for OP27 in 8-channel mixer

I was thinking about building the 8-channel mixer project from your November & December 1996 edition. Can you please tell me where I can get the OP27 op amp or can a substitute be used? If so, which one?

Also I don’t intend using microphones, so can the SSM2017 be omitted and the line signal connected directly to VR1 on IC2a (LM833)? (E. Z., via email).

Dick Smith Electronics have the LM627CN which is a direct pin-for-pin equivalent of the OP27. And yes, you can link the line signal to VR1.

Gain controlled microphone preamp

I have built the gain-controlled preamp described in August 1995 for use in our church. On setting up, using two different microphones, the open R1 is too sensitive with significant hiss and a tendency to run into feedback but the next set of values in Table 1 are not sensitive enough.

There is a non-linear relationship between R1 and the parallel C. I am not sure how to select the resistor/capacitor pairs. Would the pair 6.8kΩ and .0047μF be satisfactory to try as an intermediate set of values between open and the first set of values in Table 1? (G. C., via email).

The value of capacitance is not overly critical. You could use a trimpot for R1 to vary the gain instead of a fixed value. A value of 20kΩ would allow variation in gain over the range required. The use of a .0047μF capacitor would be a good compromise value. For a fixed value of resistance, try 10kΩ and .068μF capacitor.

Reflector for beat-triggered strobe

I was wondering where you got the reflector used in the prototype of the beat-triggered strobe described in the August 1998 issue. I have built the PC board but after quite a bit of shopping around, cannot find a suitable reflector around the size specified, except as part of a very expensive CFL downlight fitting. Most start at about 300mm (way too big) or below 120mm.

I would appreciate any help you could give to point me in the right direction. (J. V., via email).

Those spun aluminium reflectors used to be available as a part from kitset suppliers but now are only available in the kit from Altronics. Have you thought about using a large semi-sealed beam headlight from a wreckers? Might be worth a try and would have the advantage that the front glass is integral.

Dead display in digital tacho

I have built the digital tacho featured in the April 2000 issue of SILICON CHIP. The problem is that when power is applied only "LO" appears in full height on the display (in the two centre LED segments). I have replaced the PIC with a new one purchased from Jaycar but to no avail. Nothing happens when you press any button. (L. R., via email).

Your problem could be that the switches S1-S3 are oriented incorrectly. Try rotating them through 90 degrees. Alternatively, you could be lacking a connection between the two PC boards. Check the contacts between the 7-way sockets and pin headers.

Adding memory to the Wavemaker

I enjoyed the article on the Wavemaker in the January 2001 issue – a very practical solution, well implemented. For our application, it would be an advantage to have the capability of storing a single computer-generated complex wave on the PC board so it could be played back continuously. Thereby, the device is not dependent on the presence of an external computer.

Can you advise, in general design terms, how you would approach this modification? (P. N., via email).

It would require a complete redesign of the Wavemaker to allow on-board storage and replay of waveforms. As well as storing the waveform file in memory, you also have to save the information regarding its length and/or replay speed. It gets fairly complex.

A design for a waveform generator along these lines was described about three years ago, in another Australian electronics magazine. That design might be of interest if you do need a generator that can store the waveform on board.

High power light dimming

Just recently the need has arisen for a high power (1200W) incandescent lamp dimmer and delving through my library of SILICON CHIP magazines I found the article on a Heat Controller in the July 1998 issue and a High Power Dimmer in the August 1994 issue. Now I realise the Heat Controller is clearly not designed for the job of lamp dimming but I am very attracted to the simpler design (there is no transformer for a start).

Would it be possible to adapt your circuit to lamp dimming duty by increasing the operating frequency of the oscillator or are there other complications that would make this too difficult? (R. M., via email).

The Heat Controller cannot be used to dim lights although your thinking is on the right track. The problem is that the mains frequency is fixed at 50Hz and the heat controller varies the power by applying bursts of 50Hz sinewave to the appliance. The minimum burst is one 20ms cycle.

So no matter what you do with the burst rate, a heat controller like this, relying on zero voltage switching, will always cause really severe flicker if used to control power to lights. However, if the mains frequency is increased to 400Hz, as it is on aircraft, then this system of light dimming does become practical.

LED displays for bright sunlight

Some time ago I purchased and built a couple of the Digital Speedo kits, as featured in the November & December 1999 issues. They are excellent. However, the car in which they are used has a serious problem with reflective light and in bright sunshine the numerals are virtually illegible.

I ignored this until I purchased a digital voltmeter kit, which has numerals which are much brighter and very easy to read. I have no need for dimming capability. So my question is, how can I make the digital speedo display as bright as the digital voltmeter display?

I have disconnected LDR1, VR1 is up full, and changing the seven 150Ω resistors to a lower value has not helped. I think that changing XTAL1 may fix the brightness problem but may change the readings. Can you help? (P. W., via email).

While it may seem that the displays used in the speed alarm are of a lower emission output compared to the voltmeter, in fact both projects should have the same light output if the recommended displays are used. Perhaps you purchased the parts from a different supplier?

Where the display is used in bright ambient light conditions we would recommend using the sunlight readable HDSPH151 which produce 16mcd of light at 20mA compared to the 1.3mcd from the HDSP-5301 displays. HDSPH151s are available from Farnell Electronics (Cat 264-313). Phone 1300 361 005.

Don’t drive speakers too hard

My two main speakers in my hifi system blew a midrange driver whilst testing (at high volume). They are an Epicure model and were supposed to have been rated at 100W. I was sweeping the amplifier with a signal generator at 50W RMS output, about 2/3 the amplifier’s capability. (I thought we had a resonant frequency problem with the setup and was trying to find it). I ran the system at 1kHz (clean and undistorted) for about 40 seconds or so and then it fizzled.

Now why did the midrange driver blow? If the speaker is rated at 100W, shouldn’t it be able to take 100W across the frequency range it’s rated for?

Having said that, my problem now is replacing the Epicure midrange driver. And what’s to stop it from happening again? (M. S., via email).

Most speaker ratings refer to normal program material so a speaker rated for 100W would comfortably handle the full output of a 100W amplifier (not driven beyond clipping) on normal program (ie, music) material. The problem is most program material, even rock which has a pretty narrow dynamic range, still would have an average power level of only a few watts, with the amplifier being driven to the onset of clipping.

By feeding in 50W you were really going over the top and it is a wonder you weren’t deafened. Even a couple of watts on sinewave over the midrange is really deafening on most speakers.

The moral is this: if you want to test on sinewave, check that your speakers are rated for continuous power. If not, assume they won’t handle it and keep the volume down to the merely loud, otherwise you will easily blow tweeters and midranges.

High efficiency fluoro inverter wanted

I have constructed three 20W fluoro light inverters, as described in the February 1991 edition of SILICON CHIP. All perform brilliantly and have cut power consumption by nearly 50% on our solar power system.

I have also built the 40W inverter, described in the same article but this has not performed to expectations. While powering a 40W tube, the inverter would not draw more than 2.8A when fully warmed up and the secondary voltage measured up to be around 600VAC. When powering a 36W tube only 2.6A could be drawn.

The transformer consisted of 500 turns of 0.25mm enamelled copper wire, wound on an ETD29 bobbin, for the secondary and 12 turns of 0.5mm ECW, centre tapped at 6 turns, for the primary plus the base windings. The cores used were made from F44 material rather than N27 stuff and were gapped at 0.6mm to achieve the results above.

I tried larger air gaps but the inverter would only fire the tube and settle drawing nearly 4A, with the tube glowing dimly. So I wound another transformer, this time with the secondary consisting of 5 full layers of 0.25mm enamelled copper wire. The instructions aren’t particularly clear for winding the 40W transformer. Winding 5 layers of 0.25mm will make 400 turns all up.

I tried this transformer and ran
a 36W tube at 700VAC, with the inverter drawing 2.2A. The transformer cores were gapped at 0.44mm, just like the instructions said. The ballast capacitors are rated at 500VAC but still work.

Could you please advise me on what to do to make this circuit work properly? (N. R., via email).

It is impossible to produce a high efficiency inverter for a 40W fluoro using bipolar power transistors such as TIP3055s. Their gain is low and so is their Ft which means that they cannot switch efficiently at high frequencies.

The only way to get high efficiency is to use Mosfets and run at frequencies of 100kHz or more. We produced such a design in the November 1993 issue.

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.