VideoScope improved with rack and pinion
I loved the VideoScope project in the October 2001 issue of
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!
Wynnum North, Qld.
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
On further tests it was found that there was a definite 2nd
pole to the frequency response that was not explainable from the circuit
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.
Dept. of Applied Physics,
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
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
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
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
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
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.
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
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
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.
Morphett Vale, SA.
Comment: thanks for the support. We're here for the long term and we have no
intention of changing format.