Standby power in HD set top boxes
I bought a HD set-top box (Digicrystal) in Adelaide. As with
the Tevion TEV8200 reviewed in the March 2008 issue, it also had a large standby
It appears that in standby mode it merely removes the program
content from the video signal, so the box "appears" to start up almost
instantly. All well and good, except my video set-up has an automatic switch box
(Jonsa Ellies) to direct the most recently switched-on video signal (DVD, SD
box/recorder, HD box) automatically to the amplifier and TV. As the video signal
is always present, the auto switch box ignored the HD box after the first
I returned the Digicrystal HD box and have since bought a
Topfield TF7010HT HD set top box (also the same price – $198) which does switch
to full standby and works perfectly.
I always find SILICON CHIP
interesting each month and have built many kits since issue No.1.
Victor Harbor, SA.
Micro projects need more software explanation
Your February 2008 editorial raised some interesting points
regarding magazine content. Firstly, as you have said, your magazine has many
microprocessor-based designs and I dare say John Clarke must know just about
everything there is to know about using the PIC processor considering the number
of designs he has come up with. Do I think there are too many micro based
projects? On balance, I would say no.
If I look back at my "pre-micro" magazines (I collected EA, ETI
& AEM when they were published and of course, SILICON
CHIP, for more years than I’d like to admit to), the range of projects was
far more limited. I much prefer the diverse range of projects you continue to
cover. I think it’s a credit to you that you continue to dream them up!
As an electronic enthusiast for over 40 years, I prefer to try
my hand at new things. In fact I now put together more practical projects, most
using the mighty PICAXE processor, than I ever did in the past.
I often use parts of a circuit you have published and modify
them for my own purpose. If a micro can save dozens of logic ICs I’m all for it
and I don’t consider it diminishes the excitement I get making something
The one criticism I do have is the lack of detailed software
explanation. You seemed to put more effort into this side of your projects a few
years back but I don’t see it as much any more.
I use the PICAXE chip as it’s very easy to program and you
cover this quite well in your articles. If some of your simpler PIC designs gave
a more thorough description of the software program and or some more tutorials
on programming, it would prompt me to be more adventurous and maybe then I can
try to modify your programs and hardware for my own projects.
As for your second comment on projects and technical articles,
yes, I would like to see a few more articles, particularly around theory. ETI
had a great series called "Lab Notes" for a few years. Even EA’s "Let’s Buy An
Argument" series had lots of interesting technical topics.
Notwithstanding these comments, your current format with its
emphasis on well-designed projects has outlived all of your competitors. Please,
fine-tune as you like but keep the basic format as it is.
Finally, as I congratulate you on your 20 years of publication,
I do wonder how you will eventually change
over to a new guard. Most of the
SILICON CHIP staff appear to go back many
years and I do worry that the next generation will not have the same
fascination, commitment and resourcefulness currently shown. Or are there young
adults out there that share the same passion? I only hope there are.
Glen Waverley, Vic.
Comment on microcontroller projects
It has been impossible to ignore the proliferation of PIC-based
projects in SILICON CHIP over the last few years. And
while I agree with your reasons for basing projects around microcontrollers,
there are some negative spin-offs. I don’t see how PIC-based projects will offer
the same opportunities to learn about circuit design, the effect of individual
components on the whole or the ability to add and delete functions.
I am not suggesting that microcontroller projects should banned
from SILICON CHIP! They provide a learning
opportunity of a different kind, as well as projects which, as you correctly
observe, would not be feasible with any other design approach. But I hope you
will continue to develop and publish circuits built around conventional discrete
RF projects wanted
Your Publisher’s Letter in the February edition has prompted me
to write. First, congratulations on reaching 20 years. I thoroughly enjoy every
issue and appreciate all the hard work that goes into designing the projects as
well as the rest of the magazine.
I do like microcontroller projects as I have the software and
can program PICs but it would be good to balance it out with projects that use
normal components too as this helps beginners learn electronics building
I am not a radio amateur but I am interested in RF stuff, as
follows. How about a project for an RF oscillator for aligning AM and FM radios?
Many readers have asked for a TV field strength meter. Maybe a set-top box could
be modified to do it?
Furthermore, how about a demodulator probe for tracking a video
signal through the IF sections of a TV set and a piezoelectric clamp that
attaches to the injector pipe of older diesel engines to fire a timing
Circuit Notebook: a few observations
I have a couple of minor observations in respect of two items
published in the Circuit Notebook section of SILICON CHIP for
(1) The PC cooling fan driver on page 71 has no hysteresis. I
think that the fan could hunt around the set-point whenever the +5V rail
fluctuates, as it does during variations in CPU load.
(2) The alternator controller on page 68 suffers from two
potential problems. The first is that the battery will discharge into the field
winding at a maximum rate of ~4A if the motor stops for any reason. To prevent
this, I propose that the field section be powered from the alternator’s exciter
diodes. The initial self-excitation current could be provided by a momentary
start switch as in this example at:
The second problem is that a flat battery will be subject to
the full output of the alternator which could be 40A or more. I propose current
limiting the output as in the previous example (suitably adapted for a high-side
Barrack Heights, NSW.
PC boards still use
I read with a touch of amusement some of the readers’ comments
about being aghast at the magazine expressing some parameters in the old
Imperial units and not in current trendy metric.
Domestic TV sets are expressed in "cm" (diagonal screen size)
but an odd thing is that if you take the back cover off the TV set, the actual
size of the TV monitor may have, embedded in raised glass (as poured from the
factory), the size expressed in inches.
All computer monitors are proudly in inches and of course,
99.99% of all integrated circuits have 0.1-inch pin spacing.
Industrial electronics remains in Imperial, as does aviation
which still uses feet above sea level (and pounds of fuel). The Navy use fathoms
below the keel and I note that the Bathurst 500 (or whatever) motor race now
refers to pounds of fuel and the competitors are not permitted to use litres any
A large circuit board company here in Sydney had to close not
long ago because they accepted a contract for a large order from a European
Telco with all dimensions of the circuit board expressed in metric, with the
result that their CNC drilling machines could not drill the boards within the
contract time, due to the slowness of a 0.1mm XY axis movement (rather than the
normal 25-thou hop, step and jump). 99.99% of all CAD-designed circuit boards
are SI’d in Imperial not metric.
So do not be so quick to discard the Imperial measurements when
there is really nothing equivalent in metric.
RCS Radio Pty Ltd,
Chester Hill, NSW.
Hardware still comes
in Imperial sizes
I was bemused by the gripes of your correspondents, T. Robinson
and Ray Smith, regarding the triviality of a few Imperial measurements in your
February 2008 issue. Mr Robinson, in particular, was rather childish in my
opinion, by threatening to stop buying the magazine if he sees Imperial
references. I bet he wouldn’t!
Personally, I find "litres per hundred kilometres" to be
useless. We buy fuel by the litre, so why not a more useful "kilometres per
litre"? I shouldn’t have to fool around dividing figures.
Mr Robinson asks who still uses Imperial units. Bunnings
hardware stores are full of them! Buy a length of plywood and you can get
1800mm. Why not 1.5 or 2 metres? Because 1800mm is approximately 6 feet. And it
used to be 1840mm incidentally, which is almost precisely 6 feet.
Or you can buy 2400mm (rather than the more logical 2.5 metres)
which is the old 8-foot length. Better yet, buy it by the lineal metre, which is
3.66 metres or dare I say it, exactly 12 feet; an astonishing coincidence!
Having a Stratco catalog in front of me, I see roofing sheets
with a width of 762mm – down to a measly two millimetres? The weird thing is
that 762mm is exactly 30 inches or 2.5 feet! Wall siding at 1220mm is exactly 4
feet. Why are ladders 1.8m or 2.4m instead of 2m or 2.5m? Because they used to
be 6 feet or 8 feet and basically, they still are! There are lots of odd metric
sizes with some equalling precise Imperial equivalents, and the rest being near
as hardly matters. We still buy Imperial sized items; they just give us metric
Mr Smith could go to an auto parts store where he can buy a
2000 lb winch or view many other products having Imperial references – not
equivalents but delineations. Read a car magazine or watch Top Gear and it’s
nearly all MPG, cubic inches and foot-pounds of torque. Mr. Smith should also
check the diameter of his car’s wheels! And might I add, it wasn’t all that long
ago that TV screens were still quoted in inches, with metrics more of an
addendum. Many rulers and tape measures are still marked for both systems and I
expect forever will be.
I love metrics. I’d much rather measure down to the millimetre
than 13/64ths any day. It is so beautifully simple: a litre of water weighs one
kilogram and one thousand of them will fit into one cubic metre and weigh one
tonne. And there is the simplicity of the millimetre and its decadic multiples.
But nobody should be so blind as to think that the Imperial system is nowhere to
be found. Look around, it’s everywhere, and it won’t go away any time
Interesting circuit doesn’t work
I had occasion to build an expanded scale voltmeter recently. I
remembered you had already published a very clever version of this, in November
2006, on page 7. This was a reprint from the "Circuit Notebook" June 1995, which
I didn’t have.
I built it in about 10 minutes and it didn’t work! I took some
measurements and pondered for a while; it’s a bit of a brain-teaser. The problem
is that the 7805/7905 devices are designed to source current to the load, and in
this case the current is flowing the other way back into both the regulators.
This causes the regulation to fail and the output terminal voltage to rise (with
respect to its GND pin).
The 7905 was much worse than the 7805. With only 1mA flowing
backwards into its output pin, the voltage rises to over 6V. I tried a number of
regulators from different manufacturers but they were all the same.
To explain the problem, if we assume 12V is applied to the
input, the output pin of the 7905 will be sitting at +7V (ie 12V-5V) with
respect to the input minus. This +7V has a current path via the meter to the 5V
output of the 7805, thus tending to pull the 7805 to a voltage above 5V. The
same happens to the other regulator.
In order to fix it, you need to ensure current is always
flowing out of each regulator. This requires a load resistor from each output
pin to the respective GND pin. I would suggest that, to keep it stable, about
five times the current should flow via this resistor, ie, 5mA through the
resistor and 1mA through the meter.
I am surprised that Wal Douglas claims to have used it
successfully for years.
Telstra – Wireless Engineering & Operations,
Comment: well you have uncovered a mess. We did not spot the
problem in 1995 and we didn’t spot it again in 2006!
Comment on Prius battery life
I can’t believe you published Gorton Drennan’s letter without a
warning about its accuracy. His assertion that the Prius’ battery has to be
periodically replaced is not true. Toyota claims the battery will last the life
of the vehicle. They achieve this by ensuring the battery is never fully charged
Mr Drennan has confused the expression "limited capacity" with
"limited life". The limited capacity (4Ah) and extra weight of the Prius means
that when it is used for any purpose other than city driving, it will not
achieve better mileage than many conventional petrol vehicles.
Port Macquarie, NSW.
Comment: in fact, the battery does not last forever. We
recently had a correspondent who purchased a grey-market import (ex-Japan) 1999
Prius in which the battery has failed. Toyota apparently will not help because
the car was not purchased from a Toyota dealer.
I was about 10 when we went metric, so became conversant in
both metric and Imperial systems. I became familiar with SI units through
physics and can happily work in several different number bases.
However, I have never been able to get familiar with
kilo-parsecs per 100 litres (or whatever) or hecta/megapascals. MPG and PSI
still hold a lot of meaning to me, as well as for a large number of other
people. Pray you never need to work with old English equipment, when it seemed a
new thread was invented for every application!
If seeing MPG on a magazine cover is so distressing to
Robinson, I hope the editorial staff at SILICON CHIP never
show a valve project on the cover again. Presumably, medical assistance would be
Comment: you should realise that the metric thought police will
be around to your place shortly.
DDS VFO project feedback
I have recently acquired an RCA 89P WW2 (1942/3 build) 2MHz -
20MHz AM crystal-controlled transmitter. This was used on WW2 warships and was
built like a rock, weighing in at a shade under 350kg. This is a long-term
restoration project and part of the idea was to convert the crystal oscillator
to a VFO.
The DDS VFO article in the March 2008 issue was exactly what I
was looking for, so I have embarked on acquiring the parts. The display
interested me as I have a few other projects that could use this approach, so I
did a search using a popular search engine.
I read around 30 or 40 hits, finding prices ranging from $9 to
$61. The $61 was in the first few hits, the $9 in one of the ones much further
down. (Tip: when using a search engine, look beyond the first page of results,
especially if you want to find the good prices.)
I was pleased to find an Australian supplier of the display
(Peakhour at www.peakhour.com.au). I
ordered a few for the various projects, paid online and they were delivered in
two working days. One of the units was damaged in transit and I emailed Peakhour
with a photo and they dispatched a new unit on the same day. Ah . . . customer
service as it used to be still exists.
Video on soldering SMDs
Following your article on soldering SMDs in the March 2008
issue, there is an excellent video on this topic at http://www.curiousinventor.com/guides/Surface_Mount_Soldering/101
South Oakleigh, Vic.
Comment: thanks for the link although we have to say that we
would rather hear the Americans refer to solder as "solder" instead of
On page 4 of Mailbag in the April 2008 issue, the writer is
bothered by television stations identifying their transmission. In fact, I
actually find this handy.
Very few modern television sets have channel identification
numbers on the front panel. The last TV I owned which showed which channel had
been tuned was a 1998 Philips. Newer TVs need a press of the remote control to
reveal the station you’re on whereas the watermark allows me to see the channel
at a glance.
I never find the logos intrusive, as they are "translucent".
One can still see the picture behind it. As for sticking a grey paper over the
watermark, what does that achieve – only a worse distraction?
The watermark is handy when the program memory location numbers
don’t equal the channel numbers. For example, my mother has been in hospital
three times in the last few months. The TVs there don’t display actual channels,
only program memory numbers. When I subscribed to cable TV, watermarks were used
frequently – including when viewing a recorded program; you knew where you’d
recorded it very easily.
Albert Park, Vic.
PICAXE circuits are not
the only winners
I have noticed a big trend towards PIC-based projects. More
worrying is the appearance that the only circuits that have any chance of
winning the Circuit Notebook prize are those that include a PICAXE. I have been
put off submitting my ideas and circuits because of this. I wonder how many of
your readers are in the same boat.
I have built a lot of projects in my day and have found that
micro-controlled projects tend to do what they are claimed to and have greater
reliability. Is this a good thing? I’m not really sure.
I remember building the 240VAC light chaser some years ago. It
was a big kit with some 300-odd components and it took a couple of days to
build. What I remember most is what I learned about fault-finding in getting the
thing to work. It was most frustrating but in the end rewarding and I did it
Maybe we need a mix of projects and some more "back to basics"
articles on microcontrollers for us old guys out there.
The other thing I have noticed with PIC kits is that their
price is generally between $70 and $100. I sometimes find it hard to see the
value in kits like the "PIC-Based Battery Voltage Monitor" (SILICON
CHIP. May 2006) for cars which retails for around $70 when you can buy an LCD
module for around $20 that will do the same job. Hobby electronics is no longer
cheap and some people will find it hard to justify the growing cost of kits. So
maybe some low-cost projects could be added for these readers too.
Waurn Ponds, Vic.
Comment: with regard to the matter about Circuit Notebook items
only being winners if they use a PICAXE or PIC, we can see how you could easily
get that impression since there have been so many winners along those lines in
the last 12 months. However, that is not intentional and we have had non-PIC
winners in the March, April, May, August & December 2007 issues and in the
March & April 2008 issue.
In judging the winner each month, we are looking for ingenuity
and if the circuit involves a PIC/PICAXE and is ingenious, then so be it. But we
would love to have a larger variety of circuits – if you have some, please send
them in. Having said that, there is no guarantee that they will win or even be
published (we can be hard to please . . .).
As far as kit prices are concerned, if you look at them in real
dollar terms, they are still good value for money compared to kit prices of 20
or more years ago.
Impedance bridge does not measure impedance
I must comment on the Impedance Bridge in Circuit Notebook on
page 70 of the March issue. I realise that this is not your circuit but one look
at the actual bridge circuit shows that it can only be used for resistance
measurements (much simpler to do with an ohmmeter). If the unknown is in any way
reactive, the bridge will not balance, or be correct.
For instance, if the unknown is a pure reactance of half the
value of the multiplier (ie, an impedance ratio of 2:1), the minimum balance
reading (which will be very broad and some 40% of the input voltage) will occur
at a 4:1 ratio of the range switch.
As is well-known, impedance bridges must have a compensating
reactive component in one of the branches. Even for resistance measurements
there is a problem as, with the values shown, the maximum resistance that can be
measured is 10kW! And of course, no need for choice of frequency. Sorry to spoil
Pascoe Vale, Vic.
Old inverters had lots of interference
In the February 2008 issue, Rodney Champness had an interesting
article on old inverters. I grew up on a property in northern NSW with a 32V
lighting plant. The important thing to remember about these installations is
that they were just that: "lighting plants".
Owners often forced them to do more than just illuminate, eg,
operate power tools, etc. Most could not oblige unless you ran the generator as
We had one of the little Ferris inverters as illustrated in the
article. Having a 33kV line running right past our home, we lived in hope of
"Town Power" and so had some small 240VAC appliances. The inverter was bought to
operate 240VAC electric razors and a battery/mains portable radio. We soon found
the interference Mr Champness mentioned.
On enquiry to Ferris we were told that these inverters were not
intended to operate radios. Their attitude seemed to be that if one wished to
use radios, it would be better to buy an inverter or genemotor that operated at
50Hz. These were available but were very expensive and inefficient.
Of course, at a vibrator frequency of 100Hz, the rather
rudimentary power supply filtering in battery/mains radio sets would not have
been very effective. But like Mr Champness, I think that the RF filtering could
have been better.
Microcontroller articles are appreciated
As a regular purchaser of SILICON CHIP, I am
responding to your February 2008 editorial where you ask for comments re future
articles. I am a farmer in East Gippsland, Victoria. I expect that I would be
classed as something of an experimenter in electronics but I do take that
further to a point where I build helpful and reliable devices to assist around
our home and our farm.
The trend towards microcontrollers: I really appreciate
these articles, so keep them coming. It would be a retrograde step for you to
ignore their existence and to replace their function with complicated circuitry.
One uses an 8-pin 555 timer without a second thought so why single out, say, the
8-pin PICAXE or PIC as being too complicated?
If you set out to ignore them, you might as well close the book
on solid-state and go back to having everything operating with thermionic
valves. I consider that PICs are incredibly useful and foresee utilising them in
various projects in the years to come.
However, I am continually surprised at how many people in the
electronics business know almost nothing about the PIC programmers. And I have
to admit, were it not for Stan Swan’s series of easy-to-read and understand
articles on them, I would have had a lot of difficulty in coming to terms with
Even with his articles, I was sure that I was going to
seriously damage my computer with the serial port link to the device but that
didn’t happen. The BASIC language they use is not hard; in fact quite
fascinating to create, to program into the device and to see whether it does
what you want.
In looking for a direction for the future, I think that you
should, no, you must publish very elementary projects like Stan’s on a regular
basis. There are a lot of people to be brought into the PIC fold and the more
complicated projects will not entice them into it.
Emphasis on electronic projects as against articles about new
developments: I see your magazine as a constructional one and that your
present approach is the best. I recall ceasing buying Electronics
Australia because it had too much on new developments and nowhere near
enough comparatively simple constructional projects.
Instructional detail: if one decides to undertake a
particular project, you just cannot have enough detail. Your writers do an
excellent job and it would be a shame to see that reduced in any way. The
consequence of too brief a description is failure of the project.
Internet: I live in an area where rural telephone wires
have made ground access to the internet pretty much out of the question. Our
only solution would lie with satellite coverage but the cost has been a problem
for us. So, with no access, when an article suggests that part of the project
information, say for example, a PIC program, should be obtained via the
internet, we are in trouble.
Still, I expect that we are the exception and there will be an
ever-increasing reliance upon it for such references. Perhaps you could give
some consideration to those folk who are for whatever reason, without internet
Comment: we can make software available on CD-ROM for $9.50 including