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VideoScope improved with rack and pinion

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I loved the VideoScope project in the October 2001 issue of SILICON CHIP. I just could not wait to get it up and going. However, I changed a few things for my own convenience. I used a rack and pinion from an unused camera tripod and turned a small wooden stand to fit a glass dish.

This makes focusing far easier. I study and collect ants and only need low magnification, 80-120. Other improvements would be a bellows between lens and CCD camera. I only used a B&W camera but was amazed at the picture quality. Top project!

G. Reynolds,
Wynnum North, Qld.

Critical transistors

I recently assembled a kit for your Ultra-Low Distortion Amplifier (described in March 2000) and in bench testing the finished product discovered the following. Distortion at supersonic frequencies was chronic and the waveform was covered in spurious garbage that would do awful things to many tweeters!

On further tests it was found that there was a definite 2nd pole to the frequency response that was not explainable from the circuit design.

The output devices supplied were genuine Motorola so suspicion fell on the MOSPEC-branded MJE15030/31 driver transistors. They were removed and tested and found to bear no relationship to quoted specs. Gain was very low, Vbe was erratic and Ft was in the kHz region!

Replacing them with a reliable branded type completely cleared the problems, giving clean waveforms well beyond 100kHz. As kit suppliers no doubt buy these devices in by the truckload, I imagine there could be a lot of substandard performing (if not dangerously unstable) amplifier kits in the field by now. Hope this alert is of use.

Kerry Williams,
RMIT University,
Dept. of Applied Physics,
Bundoora, Vic.

Comment: this is correct - you must use genuine Motorola or On Semiconductor devices for the MJ15030/31 driver transistors in the Ultra-LD power amplifier. These same comments apply to the power amplifiers used in the Ultra-LD 2 x 100W RMS Stereo Amplifier.

Concern for copyright

I am responding to your editorial in the December 2001 issue. I guarantee you that I have never photocopied your magazine. Not so long ago my wife Pip was leaning over my shoulder to read an article and I instantly closed the magazine and said she would have to buy her own copy.

By the way, how about doing some interesting investigation. 3-pin mains plugs like those we have in Australia seem to be the same as used in parts of China, New Zealand and Argentina. Where did our 3-pin plug and socket design come from and why are they the same as used in those other countries?

Dick Smith,
Terrey Hills, NSW.

Transformer power rating for half-wave rectification

In the "Ask Silicon Chip" pages of the November 2001 issue, a reader asked why the transformer power rating for a centre-tapped two-diode rectifier is 1.4 times that for an equivalent full-wave bridge rectifier, as noted in an ARRL handbook. You responded that the "VA rating" would be the same either way.

Vague recollections of my undergrad days percolated up as I read the letter and your response and I do believe the handbook is correct. For a given output voltage (V) and current (I) into a resistive load, a centre-tapped two-diode rectifier must be rated at a total 1.4 times average power: each winding is conducting only half of each cycle, which means that the RMS power in each winding is halved or
0.5 x 1.4 x VI.

However, the total transformer rating (ie, both windings) would be 2(0.5 x 1.4 x VI) = 1.4VI, or 1.4 times that for a bridge. So the centre-tapped configuration saves cents on the diodes but costs dollars on the transformer. I can't imagine it ever being used outside of academic study.

Ben Low,
via email.

Comment: in responding to the question we did not consider a resistive load since that is extremely rare. We considered it only for a capacitor-input power supply where the rectifier duty cycle, for both full wave and centre-tap configurations, is typically around 10% or less. This makes the 50% duty cycle consideration of a centre-tap transformer feeding a resistive load quite academic, as you suggest.

Windows XP review leaves questions unanswered

I just read your review on Windows XP in the December 2001 issue. All well and good and it was an interesting article but the review didn't go far enough, in my opinion. I know you are not a computer magazine, therefore the review should have covered some of the things that are of more relevance to us electronics types.

What should have been included was stuff like: How does it go when I want to program my AVR via BASCOM on a Dontronics DT006 board? Will the PIC programmer you published a while ago work with XP? Will Atmel's AVR studio work? What about the Mini and Maxi ABC boards and their software, or all the other projects that need a computer to program a micro, etc?

The main reason for those questions is that XP is based on the Win2000 core, which does not allow control of the parallel and serial ports by other applications; at least not without a lot of convoluted patching and loading of special programs that release the ports for general use, maybe! And XP is different to Win2000. A few mates of mine upgraded and a lot of their stuff, EPROM programmers, microcontroller programmers, etc that worked with Win2000 no longer work with XP.

Sure it is supposedly up to the developers of those projects and products to put out a patch for their software to run on XP but that could be many months away or never, if the redesign project is too big. In the meantime, everyone who converts to XP expecting everything to work will be sorely disappointed. According to my mates, the ability of XP to emulate a previous version of Windows did not work with their equipment.

Yes, you can set up a dual-boot system, Win XP or Win 98. But then why bother with XP? - might as well stick with Win98 for all it's faults.

Is it worth your while to have an update to your Win XP article explaining the above or giving details of how to get everything working again? I for one won't even consider XP until I know that all my stuff will work.

There is no point to an OS that just adds a lot of "fluffy eye candy " and otherwise is not really better than its predecessors. All the multimedia stuff is another thing entirely and has nothing to do with my main point.

Keep up the good work. While I'm not a subscriber for no other reason than I never got around to it, I get every copy every month and have every issue since you started. And yes I agree with the editorial. Every one should go out and buy the magazine.

Ralph Teichel,
Ringwood North, Vic.

Comment: putting out a fairly comprehensive review of XP, as we did, is one thing. To try and answer all the sorts of questions you raise would take many weeks of work and then still leave many questions unanswered.

Electric vehicle article appreciated

I would like to thank you for your excellent article by Ross Tester on electric cars in the December 2001 issue. I am a mechanical engineer, a refugee from that other magazine and welcome intellectual stimulation. I remember a number of electric vehicles in UK 30 years ago, trains, buses, milk and bread floats and wonder whether electric vehicles are blokey enough for Australia.

Imagine going down to the pub and saying "I've just bought an Electric Ute with 10 Amp-Hour battery, twin overhead terminals and turbo ventilation". How can you lay rubber with an electric car or get that satisfying roar when you drop a cog to overtake a semi. Maybe manufacturers could incorporate speakers and a means to spray paint the road black. You could download a roar or rubber squeal from your favourite website.

On a serious note I have a few thoughts on the subject. I wonder if we also need to change the current infrastructure. While lightening the car to reduce the inertia and regenerative braking are all heading in the right direction, the car is still carrying all those heavy batteries. One possible option is to carry one or more battery packs depending on usage, to reduce this weight.

Also battery changeover rather than recharging seems a viable option, with battery changeover stations incorporated in the current petrol stations. Each battery would carry a chip encoded with information such as the last user and their credit details, the battery condition, etc. This information is downloaded to the battery supplier and credit company each time the battery comes back for recharging.

The vehicle would have its batteries under the vehicle and simply drive over a rack of batteries with their terminals on the sides touching busbars for charging/discharging and as one set of battery packs went in the other was ejected.

Looking at the hybrid engine, I see it is a piston engine. While rotary engines seem to have come and gone, they would seem to be the ideal choice for this application. Maybe Ralph Sarich's rotary could incorporate this change?

Tony Rossiter,
via email.

Lifetime support

I was horrified to read that "Electronics Australia" has closed its publication after all this time. As a long-term electronics technician both for business and pleasure, I rely heavily on information and ideas that appear in your magazine.

I am hoping that you are not going to abandon us in the near future. Your magazine is my lifeline. I would be lost without you so keep up the good work. You have my full support for ever.

Kerin Sharp,
Morphett Vale, SA.

Comment: thanks for the support. We're here for the long term and we have no intention of changing format.

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