Headphone amplifier solution for serious hearing loss

With respect to the item on serious hearing loss on page 101 of the February 2007 issue, I too have a serious hearing loss problem with, effectively, one ear useless and the other cutting off quite sharply at around 5kHz. Combined with severe tinnitus, this leaves me straining to hear dialog from the TV, particularly female voices.

Some moons ago I purchased a Super Ear kit ("Electronics Australia", May 1998) from Jaycar (Cat KA-1809). This has proved to be a boon which provides more than adequate audio HF boost, enabling me to enjoy TV programs with satisfactory resolution of all AF frequencies within the normal speech band. I would recommend this kit to your reader, W. B.

Ernie Blankley,
Brisbane, Qld.

Help with
B&W picture tubes

I just could not help but smile when I read the introduction to the Servicemen’s Column in December 2006: "Imagine watching a TV that’s now 50 years old". I was doing that very thing some two hours earlier on my AWA 21-inch 204T (with the deluxe chassis). So I don’t find it unusual. Mine gets a work out at least once a week with either DVDs, tapes or my younger kids who watch ABC cartoons.

The reason I am writing is the intriguing mention of Stephen Appleby and the replacement Thomas picture tube. I was led to believe that Thomas Picture Tubes in Riverwood, Sydney closed down in the late 1980s and the remaining stock of monochrome picture tubes went to the tip.

I have a few pre-1960 television sets which I work at restoring. They take an excessive amount of time and mostly are nearly impossible to get 100% perfect. Unfortunately, my only source of replacement picture tubes and certain other bits is from council clean ups and the problem is that scroungers hunting around for scrap metal rip the backs off these old sets, smash the neck off the picture tube and take the copper deflection yoke.

My question is: can anyone help? Are there any SILICON CHIP readers who have an ancient TV covered in junk in their garage or rotting under their house which is destined to become council clean-up landfill in the Sydney area or surrounds? I don’t seem to be able to beat the scrap guys and would love to get to it first.

I’ve almost got enough 21-inch 90° and 70° tubes (though extras would be welcome) but really need a couple of 17-inch 70° or even 90° types. These have longish necks of about 37mm in diameter with a large multi-pin Bakelite plug. These are physically quite different to the more common shorter 110° types used from around 1959 until the end of black and white TV. If anyone could help I would be most appreciative.

Thanks for all the Vintage Radio columns and the recent historical articles. Please keep them coming.

Owen Kemp,
Phone (02) 9524 0746
ake90071@bigpond.net.au

Comment: there must be quite a few old colour sets which are about to be disposed of, as well. Anyone wanting to restore old colour sets would be wise to act now and collect as many as possible before they all go to council clean-ups.

Ultrasonic Eavesdropper
and ANABAT

I got to the end of the Ultrasonic Eavesdropper article in the August 2006 issue to find that you only talked about it being used as a direct listening device.

Why not connect it to a computer running ANABAT software? This would make the project more useful and of wider practical value. ANABAT displays the call patterns of bats and identifies them and was apparently designed for bat census taking.

To find out more, got to www.titley.com.au/tanabat.htm

Pete Hutton,
Glen Waverley, Vic.

Comment: thanks for your reference to the ANABAT system. We had not heard of it. However, we doubt that our Eavesdropper circuit would be compatible with ANABAT software because their system uses different frequency division ratios and uses a zero crossing method to derive a digital version of the signal for software analysis.

Microwave oven transformer
can be rewound

I like your magazine in most cases, however the recent article on what to throw away from a microwave oven (SILICON CHIP, December 2006) really got me. You said to chuck the transformer!

That’s the most useful part of the whole thing. You cut out the high voltage secondary and rewind it with thicker wire and you have the basis for heavy-duty battery charger. Any low voltage can be obtained, depending on the number of secondary turns.

I know you don’t like telling dummies to play mains games but this is an exception, surely!

Lester Hendershot,
via email.

Comment: you are correct, of course. However, we would not recommend this to anyone not experienced in rewinding mains power transformers.

Hospital electronics requires technical backup (1)

Your January 2007 Publisher’s Letter prompted me to write. It is rare that anybody notices much in a hospital other than the front line doctors and nurses. I don’t mean to detract from the great work they do, however as a Biomedical Engineer, recently retired after 30 years in a major public hospital, it is heartening to see our work being noticed (even if it is by "one of us" so to speak).

Biomedical (or clinical) engineers and technicians look after the vast array of equipment used for patient care in modern hospitals. Inventories run into many thousands of items and tens of millions of dollars in value. Most of the equipment is electronic based but many items, such as patient ventilators and dialysis machines, are mechanically complex.

The work is exacting and interesting. Much of the equipment is used for life support or making patient treatment decisions. Routine and breakdown maintenance must be carried out with great care and a clinical understanding of the purpose of the equipment is essential for troubleshooting.

The complexity of modern computer-driven equipment, particularly in the operating theatre and intensive care, often requires technical staff to support the nurses and doctors using the equipment. This may be in the form of training or troubleshooting, or working alongside the clinicians in the ICUs and theatres.

I suppose the greatest reward in the job is knowing the value of the work you are doing – contributing to patient care – and I would encourage qualified technicians and engineers to consider a career in this field. Just contact the Biomedical (or Clinical) Engineering Department of a major hospital. Good committed staff are in demand!

John Symonds,
Sydney. NSW.

Hospital electronics requires technical backup (2)

It was great to hear of Leo Simpson’s appreciation of the vast array of "biomedical" or "electromedical" equipment on his recent visit to hospital.

I am a Biomedical Engineer and look after the service, repair and mainten-ance of all the biomedical equipment you described in your article. I work with a small team of engineers that look after Eastern Health, a network of hospitals in the Eastern suburbs of Melbourne – see www.easternhealth.org.au.

The "drip machine" is known as an infusion pump. They are commonly used for the controlled delivery of fluids and drugs to patients. There are other pumps know as PCA (Patient Controlled Anaesthesia) pumps which have a hand control that allow the patient to request a "shot" of morphine or pethadine when they are in pain. All these devices have a vast array of hardware and software safeguards that prevent over delivery of drugs and protect the patient in case of failure.

The vast array of biomedical equipment that was used during Leo’s time at hospital would not work as well if it were not for the team of biomedical engineers servicing and maintaining the equipment in the background. Most biomedical equipment requires annual service to check electrical safety and calibration and to replace commonly worn parts.

Simon Cowley,
Ringwood East, Vic.

Nuclear power reactors
could be greatly improved

I enjoyed reading the "Publisher’s Letter in the February 2007 issue of SILICON CHIP. I would like to comment in the following way. I am not necessarily a promoter of nuclear energy as the best way to minimise global warming. In some cases (China) it is worth consideration. But if one is to examine its prospects, the best implementations of this technology should be considered. I refer to an article in Scientific American for December 2005: "Smarter Use of Nuclear Waste" by William H. Hannum, Gerald E. Marsh and George S. Stanford.

This article described the advanced liquid metal reactor (ALMR) cycle as in advanced fast neutron integrated reactors. This technology has been demonstrated successfully in a prototype reactor prior to 1994. The main points are:

(1) For a given equal energy output, this reactor produces less than 1% of the radioactive waste that a conventional reactor produces.

(2) The radioactive waste that this reactor produces is less radioactive in 200 years than the waste from a conventional reactor would be in 100,000 years.

(3) This reactor can be fuelled with the radioactive waste from conventional reactors and/or decommissioned nuclear weapons.

(4) Reprocessing of fuel rods takes place in the same building complex that the reactor is in.

(5) This reactor is "passive safe". While operating, its cooling system can be turned off and it will not melt down.

(6) Because of the high efficiency of this reactor, known uranium ore reserves would serve our energy needs for many thousands of years.

G. Calhoun,
via email.

Comment: AMLR sounds very attractive but it may be many years before commercial designs exist. This is especially the case since research into the prototype IFR (Integral Fast Reactor) which incorporated the AMLR concept, was discontinued by the US government in 1994, only three years before completion. This was a seriously misguided decision, similar to the US move to kill off their electric car industry just a few years ago.

Plugpack mayhem

The Mailbag letters by Ross Herbert and Graeme Dennes in the October and December 2006 issues of SILICON CHIP respectively raised issues with plugpacks. It seems that the plugpack situation is very untidy if not bordering on mayhem. Perhaps one could stand back and take a broader view.

Our houses are supplied with alternating current. AC power is approp-riate for efficient transfer of bulk electrical power over long distances and for meeting the needs of high power domestic devices such as electric ovens, toasters, air conditioners, etc but not so appropriate for modern domestic electronics.

In the last 30 years or so, domestic and office electronic equipment has trended towards lower power and internal DC voltages, as witnessed by the variety of voltages output by plugpacks. Laptop computers are a special case that require from 15-18V DC at up to 8A!

A solution to managing this changed load type could be to install properly engineered DC distribution systems in homes and businesses. This DC system would not replace the current 240VAC system but be installed in addition. Appropriately designed electronic equipment would simply use a cable to plug in to the DC system with no plugpack or internal AC section required! An appropriate distribution voltage might be 24V DC (or a combination of 12V and 24V) to match current battery technology.

In simple form, the DC distribution system could be fed directly from the AC system through rectifiers. However, real benefits accrue if the DC system is coupled with a system containing substantial energy storage (most likely a lead/acid battery bank under current technology). The battery bank would act as a power supply buffer and AC system power spikes and brownouts would not be such a hazard to sensitive equipment.

There are further gains if the energy is derived from a non-polluting source such as a solar array. Solar systems would match a DC distribution system beautifully and are now well developed. A typical domestic solar system providing 13kWh/day out of a total daily load of 25kWh/day has been reported in the media.

Advances are being made in areas such as solar cells efficiency and high-
intensity LED lighting. Once the DC distribution system became established, it is likely more loads would switch to DC; eg, house lighting. Mass production would tend to lower installation costs with time and development of such systems would be directly transferable to developing countries where AC supplies are problematic.

Implementing a DC distribution system would not require particularly novel or new technology but would require development of standards and hardware. Additionally, manufacturers would need to be encouraged to modify their designs to accommodate standard voltages.

So maybe there is a solution to plugpack mayhem, which may also provide significant greenhouse gas savings, but implementing such a concept is more of a political challenge than it is a technical issue.

Bruce Fischer,
Giralang, ACT.

Information on
Geiger counters

In the February 2007 issue of SILICON CHIP, I saw the request from B. B. for information about a Ratec brand Geiger Counter. I can help!

As a geophysicist working in min-eral exploration, I’m familiar with the now outdated Geiger counters (also known as ratemeters) once used for uranium exploration. I don’t actually have a circuit for the Ratec instrument mentioned but I do have several old geophysics texts (1940-50s) that describe the technology and provide circuits for battery-valve instruments. These show that the Geiger tube needs about 400V DC for operation.

Also, the well-known book "Fortunes in Minerals" by Ion Idriess (1951) (available from most antiquarian book dealers) gives a detailed description on using the Geiger counter and provides the circuit for the instrument built by the Australian Bureau of Mineral Resources.

In particular, one other I have –
"Prospecting and Mining for Uranium in Australia – Notes for the Guidance of Prospectors", published in September 1954 by the Australian Atomic Energy Commission and Department of Nat-ional Development, gives quite detailed instructions for building 2-valve and 3-valve portable instruments. Again, 400V seems to be the voltage needed for the Geiger tube. In addition, it lists all the commercially built instruments available in Australia in April 1954 and the Ratec instrument is mentioned (with the approximate purchase price of 70.00 pounds) from Medical Equipment Services Pty Ltd, 79 Collins St, Melbourne. A search of the internet shows that this company still exists in Melbourne as a supplier of medical electronics:

http://www.mesaustralia.com.au/

Maybe B. B. could contact them directly for information about his Raytec 115F Geiger-Muller counter.

For further information, I would recommend that B. B. visit the library of his State Mines Department and look for other (Australian or State) government publications of that era concerning uranium exploration, as they too are likely to have further information about these instruments, and may even describe the Ratec instrument. In particular, try the library at Geoscience Australia (previously Bureau o f Mineral Resources until 1990, then called Australian Geological Survey Organisation – AGSO, now Geoscience Australia) in Canberra – the biggest earth science library in Australia.

Stephen Mudge,
Nedlands, WA.

Comment: thanks for that information. We liked your mention of Ion Idriess. He was a great Australian writer whose works have long disappeared from library shelves.

Bike Computer
Ampere Hour Meter

I was very interested to see Stan Swan’s article about using cheap bike computer plus a PICAXE micro as a DC ampere-hour meter (SILICON CHIP, February 2007) as I had been wanting such a device for my electric power-assisted bicycle.

Generally, I ride for exercise but have a number of large hills near my home and these are difficult at my age. My solution was to purchase an electric conversion kit for my 26-inch bike. It is a 200W hub motor mounted in the front wheel with a 24V NiMh battery and speed controller. My problem is knowing if I have enough battery capacity left to get up my hill at home after a long ride.

I was able to use Stan’s circuit but with a 0.01W resistor in place of the 1W resistor in the battery negative line to measure the current. The resistor was made from about 35mm of heavy nichrome wire from my junk box and carries a maximum current of 20A. The low value of resistor was chosen to minimise voltage drop to the motor.

I found I needed to set the bike computer for a 500mm diameter wheel to get a high enough pulse rate to measure low currents. Only one line of the program had to be modified for calibration. By trial and error w2=2500/w1 came out right compared to a digital multimeter.

The bike computer speedo indicates amps and the distance then shows ampere-hours directly. This was my first venture using a PICAXE which I found easy to use and understand.

Bevan Walls,
Saratoga, NSW.

 

Excellence in Education Technology Awards

May I express my appreciation to Leo Simpson and the team who produce this excellent magazine every month. The articles are varied and I think there is a good balance between general interest, cutting edge, practical projects and vintage radio. I know there has been some negative comment about valves but I really marvel at what the radio engineers achieved with them before the semiconductor revolution. That’s one reason why I appreciate the Vintage Radio section.

My introduction to radio and electronics goes back to 1954, when I built a one-valve set, a "Radio & Hobbies" project of that year. While I have taken a big detour into agriculture for about 30 years, I have come back to really enjoy this hobby in "retirement" and am back again building SILICON CHIP projects and vintage radio restoration. Hopefully, I can encourage some young person to take up similar or more challenging projects.

I was particularly pleased to see the article on Page 57 of the February 2007 issue, concerning the "Excellence in Education Technology Awards" to two HSC students, Matt McDonald and Lauren Capel. The choice of these two winners shows the learning value of widely differing electronics projects chosen by these two young people and the encouragement in this field by Leo Simpson and the SILICON CHIP staff. Congratulations!

Richard Wood,
Loxton, SA.

Radio broadcasts for the blind at sporting events

Recently, I was listening to the cricket on ABC radio when an idea came to me. They were interviewing a fellow who (I think) is the boss of Blind and Visually Impaired Cricket in Australia. He’s blind himself and was talking about his love of going to regular cricket matches but he lamented that it’s rare for a match to be broadcast on the radio. His point was that while he gets the atmosphere from being at the game, it’s the ABC radio commentary that takes a blind person to the game.

This got me thinking that there must be hundreds of thousands of visually impaired people around Australia who would love to attend sporting and other events but need more than the normal PA system to tell them what’s happening. They need the information they aren’t able to read, can’t see and which most of us take for granted.

I wonder how hard it would be to set up a national system of local broadcasting for visually impaired people (and anyone else who would appreciate it). I guess it could be AM or FM but FM is probably as good as any because of the capture effect. If possible, find a standard, single frequency in the broadcast band so that anyone, anywhere in the country would know where to listen.

The "broadcasts" would be done by volunteers. It would have to be coordinated so you don’t have a double up at any one event but this should be easy to do via a central body (website). The gear would be relatively inexpensive to produce and I guess the ERP could be limited to legal levels.

Once such a service takes off, there’s no reason why it couldn’t be extended to places such as shopping malls, tourist attractions and so on.

Paul Zucker,
via email.

 

Microcontroller projects not lightweight

I note that in the February 2007 Mailbag pages of SILICON CHIP, Ian Farquar lists the Programmable Christmas Star as an example of the sort of "lightweight" project that he would prefer to see less of. More than 100 constructors would perhaps disagree, several of whom have provided very positive feedback.

I don’t claim that the Christmas Star was in the class of those complex projects of yore that Ian praised. But what’s not apparent is that the PIC assembler source code ran to more than 1000 lines – a very far cry from the 20 lines of PICaxe code that Ian mentioned. And it took months to write (albeit part-time).

And that ties in with the point I was making my letter that you also printed in February. Much of the true complexity of microcontroller-based electronics is hidden in the (quite extensive) firmware. You rightly give the Digital Volume Control as a counter-example of a project requiring a lot of development. Yet it looks deceptively simple – "essentially a 2-chip solution", as the project description puts it. Again, a low parts count does not necessarily imply a lack of developmental complexity.

I say keep up the good work!

David Meiklejohn,
via email.

Comment: you make a very good point about microcontroller projects. For example, the software for the Programmable Ignition project currently featured in SILICON CHIP is the most complex we have developed to date. The final assembler line tally totals some 6020 lines required to perform all the functions and features required of the programmable ignition. It took many months to write and debug and represents a substantial investment in R&D.

 

Car Speedos can be wrong
while odometer is correct

I read with interest Jack Chomley’s letter in the February 2007 issue regarding his speedo experience. In 1995 I purchased a 1991 Volvo 240 wagon, which comes fitted with a VDO speedo with electronic pickup, a stepper motor odometer and a 270° needle analog speedo display.

I soon realised there was a cal-ibration problem, even though I have all standard equipment and tyres.
I made many tests; using speedometer check zones, advisory radar install-ations and lots of kilometre peg and stopwatch observations during long distance cruising trips in places like the North-ern Territory.

What is amazing is that when I read Jack’s article, I felt like he had stolen my data, as my results were identical to his! My odometer is correct to within 100m over 10km, while my speedo indicates 108-109km/h for an actual road speed of 100km/h. An indicated 100km/h gives an actual road speed of 92km/h.

My (less than ideal) solution was to fit a VDO Speed Alert unit calibrated to the correct reading and rely on it rather than the speedo when cruising. However, it is still inconvenient having to mentally convert every time I look down at the speedo.

I also noted Jack’s mention of the relaxing of the accuracy requirements
of the Australian Design Rules. Meanwhile, our technically illiterate legislators and law interpreters keep trying to reduce the allowable tolerances for radar speed checks to less than the tolerance of the equipment fitted to our cars.

Dave Heap,
Armidale, NSW.

Comment: we suspect that this big discrepancy between odometer and speedometer has been present in cars for a very long time. After all, there is a specific requirement about odometer accuracy yet car reviewers have been complaining about optimistic speedos for decades. It will probably require the successful challenging of speed fines because of inaccurate speedos before the situation changes.