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Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to "Ask SILICON CHIP" and "Circuit Notebook".

Electric cars are not viable (1)

To comment on the Publisher’s Letter in the December 2007 issue, an electric car will only do short-range commuting. If you own an electric car you have to own another car that’ll do all the other things. And pay another lot of registration and insurance and depreciation.

It’s simpler and a lot cheaper to do a dual-fuel conversion on the car you’ve got. LPG has long range and is becoming readily available everywhere. Natural gas only has short range and isn’t available generally but is delivered to most homes at cents per petrol-litre-equivalent and all it takes is a compressor at home to refill your car each night.

In a country where only a limited amount of electric power comes from anything but coal and natural gas, it’s just as climate-friendly to buy a cheap second-hand car and convert it to natural gas and just use it around town than to convert it to electric power and have to cart around heavy expensive batteries and replace them every few years.

Gordon Drennan,
Burton, SA.

Electric cars are not viable (2)

Straight electric cars for most Australian people are just fairy floss! The standard petrol engine does not just generate power for motion but also generates power for air-conditioning and electric power for all manner of devices such as ABS (and other computing/servo systems), wipers, pumps, fans, stereo systems and lighting. Headlights alone can consume many tens of amps of current!

Hybrids of some sort may be a viable alternative for city travel but come on, let’s get serious; a family trip between Sydney and Brisbane in an all-electric car is just a pipe dream with current technology.

I am not sure about the efficiency of using electricity to create motive power and any assessment should include losses from generating power at the power stations and transmission right through to efficiency of the electric motors and any regenerative braking, etc. A comparison with petrol, diesel and hybrid vehicles would be interesting but would also have to include complete end-of-life and recycling comparisons for equivalent mileage/time.

A similar study by a consortium of US manufacturers found that a diesel 4WD is both environmentally and economically less damaging than hybrids, mainly because the average 4WD stays registered for approximately 20 years and travels around 700,000km which is an equivalent lifespan to about 3.5 hybrids!

If you really want to feel good about the environment, then instead of spending $50,000 on a fancy new hybrid status symbol, buy a small diesel instead and donate the difference to your nearest university doing research into solar cells.

Prof. Jon Jenkins,
Bogangar, NSW.

Comment: we believe that electric cars will be viable. They may not ever be capable of making a non-stop journey from Sydney to Brisbane but a good many petrol vehicles cannot do the trip on a single tank either.

Electric cars are here now

I enjoyed Peter Seligman’s articles on reducing greenhouse emissions. There were, however, a couple of points I feel were not up-to-date in the third article.

The first point is regarding the range, convenience and performance of electric cars, compared to conventional cars, being way off in the future. This is clearly not true. One prominent example is the Tesla Roadster which can be seen at http://www.teslamotors.com/

The roadster has acceleration from zero to 100km/h in less than four seconds and a top speed of over 200km/h. It has a range of 390km
per charge and is able to put more than 80% of the energy it consumes to use in moving the car down the road.

At a cost of $US98,000 it is not cheap. But although not within the price range of an everyday car, the point is that the technology has come a long way in recent years. Obviously with mass production, the cost would be far lower.

Other examples of DIY electric cars which beat petrol cars in both performance and economy can be seen at:

http://www.evconvert.com/eve/electric-car-motors and

http://www.evconvert.com

Most consist of converted petrol cars. There are quite a large number of people in the USA doing this.

Greg Macmillan,

Christmas Hills, Vic.

Not enough lithium for electric cars

I like the idea of electric cars, however there is a fundamental problem that you did not mention in your Publisher’s Letter. There are simply not enough metals such as lithium for a world-scale roll-out of electric cars.

There have been a number of studies on this, including I think, one by the University of WA. If it was possible to make rechargeable batteries as good as lithium from more common metals, such as zinc, then this may be feasible but this seems to be a long way off.

On another subject, your advice to T.U. on potting compound (December 2007, page 107) is possibly one of the worst pieces of advice you have ever given. Given the sticky viscous nature of neutral-cure sealant it would be very difficult to get a good result.

Specialist fibreglass shops have available a wide range of potting compounds, including silicone ones, and should be able to advise T.U. on the most suitable one for his particular application.

Graham Shepherd,
via email.

Comment: thanks for the comment about potting compound. However, your remarks about lithium and rechargeable batteries are wrong. We expect electric cars to become commonplace, whatever type of rechargeable battery becomes the norm.

DVD players need digital the connection

I am an audio design engineer specialising in low noise electro-physiology amplifiers used to monit-or picoamp currents in human cells, so I am aware of hum and RF emission problems.

I was amazed at the poor hum and RF radiation you saw in Tevion DVD players, so I decided to check my own $50 Onix brand. I purchased this about a year ago because my "high quality" Philips player would not play home-recorded DVD or MP3 disks.

I have the Onix optically connected to a Yamaha RXV640 6.1 channel amplifier with Jamo speakers and subwoofer so if hum was a problem I would easily detect it. Optical connection is great as ground loops are eliminated.

With an MP3 disk inserted into the player and paused, I turned the volume up to maximum. I could not hear any hum out of the speakers or sub woofer. A small amount of hiss could be heard but was considered acceptable.

A radio in close vicinity to either amplifier or DVD player revealed minimal interference on AM or FM. I then turned on my LG 50-inch Plasma TV and all hell broke loose with RF emissions from the TV. It was really bad on AM but reasonable on FM. I had to move the radio about 10 metres away from the TV before noise in the radio was acceptable. Personally I would have considered this level of radiation excessive.

I cannot find any reference to CE compliance on the LG’s rear panel or in the manual but I assume it has a CE compliance certificate so RF radiation is within spec.

I also made some measurements on my system to compare optical digital and analog outputs on DVD using the headphone to monitor signals with a scope. I connected the analog audio to the CD input of the amplifier and the digital input to the DVD input, so it was easy to switch between the two sources.

The volume control was advanced so that the playing peaks of typical music were just clipped (18V p-p). I then put the DVD into pause and measured the noise from both sources. The difference was staggering!

For the digital link, the scope measured 3mV p-p of noise. I could not see any hum in the plot. Listening to the noise revealed only a quiet background hiss. For the analog input, the noise was four times higher than the optical noise at 12mV p-p and had some mains harmonics. There also appears to be a high 250Hz component.

Listening to the analog sound was definitely noisier. I could not hear any fundamental 50Hz hum but the 250Hz component can definitely be heard.

I think this is a graphic demonstration for using digital against analog signals. The DVD also has a coax digital output but I did not try that. I suspect it will be OK.

I am surprised that the Tevion was radiating so much RF as all equipment sold in Australia should have a CE compliance certificate which restricts RF radiation to low levels. Maybe you should try optical connection to remove hum and possibly ground the case of the DVD to remove any RF.

Peter Kay,

Dromana, Vic.

Comment: optical is certainly the way to go if your amplifier has the right connection.

Sputnik lasted six months

With reference to the letter by Graham Harvey in the November 2007 issue, regarding the 50th anniversary of Sputnik I, the satellite actually spent six months in orbit, not three weeks. Because the batteries which powered the on-board radio transmitter were not recharged by solar cells (as they would be now), the batteries went flat after 22 days.

Taking just 96 minutes to circle the earth, Sputnik I travelled some 60 million kilometres before burning up in the atmosphere upon re-entry. The only artefact which remains from that project is a tab which was pulled out of a receptacle on Sputnik just prior to launch, to power up the radio transmitter.

Peter van Schaik,
Tenterfield, NSW.

Low-tech water tank level meter

I have followed your articles on water tank level devices with great interest. My own system uses a weighted marine float, two pulleys, a length of fishing line and a 100g fishing sinker. Total cost: about $10.00.

Wow! No electronics and a carbon-neutral footprint.

Peter Lord,
Camberwell, Vic.

Comment: Ah, but can you read the tank level from inside your house?

Caustic soda is available in supermarkets

I was reading your article on the UV Light Box (SILICON CHIP, November 2007) where it says you can use sodium hydroxide for etching positive-resist PC boards. That is correct. I think I used one heaped teaspoon per litre of water last time I tried. Warming it up to 25-35°C will make it work faster.

The best part is it can be bought from just about any supermarket, in the washing powder section, for around $2 a 500g tub.

Michael Jeffery,
Eurobin, Vic.

Where to obtain caustic soda

I read with interest the article on the UV Light Box in the November 2007 issue of SILICON CHIP. It is nice to see a down-to-earth article such as this that explains "all" of the process.

Having produced PC boards commercially for many years, a couple of points may be of interest. First, the author says he is unable to find sodium hydroxide in Tasmania – it is readily available in most supermarkets around Australia, as drain cleaner. There are several in dry/powder form and they are 99.9% NaOH. Usually, one teaspoon to a litre of water is sufficient to strip PC boards, so to develop them would require somewhat less.

Another developer is potassium carbonate, commonly used to dry fruit. That may be a bit harder to find but I think most chemical supply companies should be able to get it.

For printing the transparency, there is a product specifically for this purpose, used in the printing industry. It is an Agfa product called "Laserlink", available from graphics supply companies. It is translucent, dimensionally stable and specifically for use in laser printers.

As for coated board material, there is another option. With pre-coated board, if you make a mistake in the exposure and/or developing stage or find a design error at the developing stage, the board is then useless. With the product below, if you make a mistake (found before etching the board), you simply strip and recoat the board and start again (no wasted board material).

Again, used in the printing industry, is a UV-imageable ink, Taiyo PER20, easily applied by the hobbyist with just a rubber roller found in art shops. It does require baking at 90°C to dry it but that is easily accomplished with an old electric frying pan.

It is expensive at around $100 a litre but get a few friends together and share it; one litre will go a very long way – many tens of square meters if applied thinly (as recommended).

Terry Mowles, Force Electronics,
Holden Hill, SA.

Oscar déjà vu

It was with some particular interest and a feeling of déjà vu that I read your article on the Noughts & Crosses machine project in the October issue of the magazine. Some years ago I was involved with the restoration of a similar machine in Melbourne.

I am a member of the Victorian Tele-communications Museum and in the process of becoming established, we formed a rapport with Museum Victoria. Since many of our members are former Telstra/Telecom/PMG technicians, it was suggested that we might be able to assist the museum with the restoration of some of their old displays. Significant in the list was their Noughts & Crosses machine.

This machine had been built in the early 1960s for the then Museum of Applied Sciences by a Mr Roy Hartkopf, an engineer in the then PMG’s Department. Many Melbournians would have remembered pitting their wits against the machine in the Science Museum until it fell into disrepair in the 1980s. It then went into storage until the prospect of its restoration was raised.

An inspection revealed that it was based on uniselectors and relays, as used in the older telephone exchanges that I had cut my teeth on. Its condition was not too good. However, with such a significant heritage, it was a challenge too good to miss and in due course it was delivered to the workshop of our museum in Hawthorn.

Countless hours were put into replacing uniselector banks, relay contacts and wiring, re-adjusting relays and generally upgrading the electrical safety and operation of the machine. Paramount in the criteria of the undertaking was that the original appearance of the machine had to be retained, both externally and the mechanics as visible through its glass front panel.

After 11 months and about 300 hours work, the machine was ready to go again. In late 2003 it was placed into service in its own little alcove at Scienceworks Museum in Spotswood. Since that time, it has played over 100,000 games and is still going strong.

Its logical sequence of operation is similar to the one that Brian Healy built back in the 1960s, except that this one does allow the player to win – occasionally.

Bob Muir, Vice President,

Victorian Telecommunications

Museum.

How to dispose of used etchant

I would like to make a couple of notes on the article entitled "A UV Light Box For Making PC Boards" in the November 2007 issue.

First, the etching needs to be done in a well-ventilated area or in a fume cupboard for safety reasons. Second, given relevant State requirements, in sufficiently dilute concentrations the used etchant may be poured down the sink. However, the outlet pipes must not be made of copper.

Unfortunately, one educational institution learnt that too late. Otherwise there are organisations that collect dangerous chemicals for disposal.

Joe Zanatta,
Werribee, Vic.

Good results with PC board transparencies

I have been using Kinsten PC boards for some years now, with great results. Up until recently, the transparencies were laser-copied by one of the commercial copy shops. The last couple of prints were less than fully opaque and it was necessary to double up a pair of copies to obtain full opacity.

In desperation, I tried using some inkjet transparencies I had on hand. These had formerly yielded similar semi-transparent prints. Finally I ran the print through the printer (HP 2355) four times. The registration was perfect and opacity almost 100%. The resulting PC board finished spot on.

The image was originally scanned from a SILICON CHIP speaker protector design and cleaned up using Adobe Photo Deluxe.

Robert Field,
Croydon Vic.

Window glass is not desirable for UV transmission

With reference to the Light Box article in the November 2007 issue, many years ago when I built my first light box it was pointed out to me that ordinary window glass is poor at transmitting UV light and that quartz glass should be used.

To quote from Wikipedia: "ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths while silica or quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350nm but blocks over 90% of the light below 300nm".

Because the operating lifetime of the UV tubes is very short (less than one year for normal UV output), it could be cost-effective to replace the normal window glass mentioned in the project with UV-transmissive glass, thereby reducing the exposure times by a significant amount and thus extending the useful life of the tubes.

Tony King,
Lilydale, Vic.

Comment: your remarks about window glass are correct and are in fact, covered in the article. Since actinic tubes radiate mainly at around 965nm, we don’t see a real problem as far as transmission losses are concerned, particularly as the tube operating times are quite short.

 

Current limiting desirable for Oscar

When I saw the "Oscar" project in the October 2007 issue, my first reaction was "Oh no, too late!" as I had intended to develop a PIC-based noughts and crosses project for submission to SILICON CHIP, quite soon. Oh well, these things happen!

But when I looked at the design, I wondered, "where are the current limiting resistors?" Clearly, the approach taken in the Oscar design, of connecting LEDs directly across the PIC’s pins, does work. You can get away with it but it’s not recommended.

What’s happening is that at least 4.5V is being applied directly across each lit LED. That would normally fry most LEDs but the current is being limited by the output drivers on the PIC’s pins. That would be OK if the outputs were designed to be current limited but they are not.

According to the PIC16F84 data sheet, under "Absolute Maximum Ratings", each pin is rated to source up to 20mA (with further restrictions on port totals), with the following warning:

"Notice: stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at those or any other conditions above those indicated in the operation listings of this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability".

In other words, using the device this way – relying on the output drivers to limit current to a maximum – is "at your own risk". Adding a 100W resistor in series with each output pin would be a lot kinder to the poor old PIC.

David Meiklejohn,
Macquarie Fields, NSW.

Comment: you are correct – the maximum current sourced by an output pin should be 20mA and the LEDs are not current limited by a resistor.

Looking at the specifications of current versus output, at 20mA a high output is typically 3.25V and a low output is 0.7V when running from a 5V supply. So the available voltage for the LED when driven by a high output for the anode and a low output for the cathode is 3.25V - 0.7V, or 2.55V.

We measured a red/green LED at 20mA and found that the forward voltage for the green LED was 2.25V and 2.2V for the red. So the current is therefore more likely to be about 22mA instead of 20mA.

Probably the PIC will survive this extra current. However as you say, 100W limiting resistors at pin 1 and pin 18 would be better.

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