Pool alarm sensor should be out of sight

I have just finished reading the article on the Pool Alarm in the September issue of SILICON CHIP.

The project revolves around a device which floats in the pool to warn if a child has fallen in or any distraction to the surgace has occurred. If you take a look at the photo on the front of the magazine, it depicts the child checking out the ball that is in the pool. However, I can almost assure you that even if the ball was not in the pool, she would certainly be equally curious about the warning device floating in the pool.

It's the old case of keeping the gate locked, the fence up to standards and anything resembling a climbing aid out of eyesight or locked down. It all boils down to the parents/guardians keeping an ever watchful eye over children of that age.

I have an idea that might be worthwhile in keeping the device out of sight. Basically it involves making the sensing part of the circuit remote (away from the rest of the control unit) and keeping it anchored nearest a pool ladder or near the edge of the pool, just enough that the device will still function.

Alex Gordon
agordon@es.co.nz

Trap in battery conversion of plugpack powered appliances

There is a trap for the unwary when converting some plugpack-powered appliances for operation on batteries, as suggested in "Battery Backup For Cordless Phones" in the October 1999 issue.

I found this out when I converted a General Electric answering machine for operation from 12V by replacing the 9VDC nominal plugpack with an external 9V regulator running from the 12V supply. This arrangement very nearly destroyed the answering machine.

You see, the designers of the answering machine had reduced the DC input voltage to the machine's internal operating voltage by simply wiring a 5.6V zener diode across the DC input - with no dropping resistor! The plugpack used had sufficiently high output impedance for this to work but my regulator circuit simply overpowered the poor zener.

Fortunately, the zener remained faithful to the bitter end. It failed as a short circuit rather than going open and allowing the 9V to damage the voltage-sensitive circuitry in the rest of the answering machine.

Equipment designed in this way may also fail if the unregulated plugpack is replaced by a regulated plugpack.

Of course, none of this would have happened if the answering machine had used a series regulator or even just a dropping resistor before the zener diode (but even this must be suitably rated for the eventuality of a low-impedence DC supply).

To solve the problem, I simply changed the external regulator to 5V. I removed the zener and did not replace it, since I did not have a replacement available at the time. However, it would have been better to replace it, to protect the machine if it is ever used again with a 9V plugpack.

Andrew Partridge, Kuranda, Qld

Health card a good idea

I would like to congratulate you on an excellent editorial, on the suggestion for a health record card, in the October 2000 issue.

Recently August 26 I entered the Alfred Hospital in Melbourne for laser ablation surgery on a 4.8cm tumour on my liver. After admission and three hours before the surgery, I told the resident doctor who came to explain the surgery all my cancer history. It had never been requested from me and I had assumed that the surgeon (whom I had never met) would have all the details on his computer. Very wrong.

I told her of my unresectable large pheochromocytoma, how it had almost blocked my Inferior Vena Cava and that I was on Warfarin to stop blood clotting. I told her about my 'moderate to severe' aortic valve stenosis and regurgitation. I told her of previous atrial fibrillations where the pheochromocytoma had released catecholamines into the blood stream and how for years I had carried ampules of Lasix with me and a syringe to inject myself if it ever happened again.

I suspect she did not believe me at first but after listening to my heart and seeing my 12-inch scar, she went to see her superiors. It turned out that the Alfred Hospital had NO access to my medical records, even though they were held on a computer at The William Buckland Institute (where I had radiation treatment twice) within the SAME grounds as the Alfred. The surgery was cancelled. It was finally done about a month later after appropriate premedication.

It is a dreadful thought that if I am ever admitted to any hospital unconscious, they will not know my significant medical history which would be vital in my case for appropriate treatment.

So yes, I fully support a smart health card. But even before that I would support the simple sharing of medical records between hospitals. It is ridiculous that my medical records at Cabrini Hospital and The William Buckland Institute were not accessible by the Alfred Hospital computers. Cabrini is only about 5km from the Alfred. Doctors at the Alfred had to ring these two hospitals and ask for the records.

But there is another, more significant problem working against a smart card which you did not mention. In Australia the patient is not legally entitled to the reports of their own medical examinations. I have found that different hospitals can and do make different interpretations of medical imaging tests. I have a CT scan where the possible lung and liver metastasis interpretation was made by one radiologist at one hospital, but was said to be an artifact and an unfilled (by the contrast medium) liver vein by another radiologist at a different hospital.

The problem of wrong diagnosis of medical tests I see as the real impediment to having medical records put in digital black and white on a smart car. Fortunately, in my case I have read up fully on my conditions and I have had sympathetic doctors who have given me all the reports. I do not want to blame anyone for misinterpretations. I recognize that the same glass can be half full or half empty, with both interpretations correct. What was an unfilled vein 1cm in diameter in December 1996 was interpreted as a possible benign tumor 2.5cm diameter in September 1999 but in July 2000 this was a 4.8cm tumor requiring immediate attention. What doctor wants to have his name electronically signed on a diagnosis subsequently found to be in error?

In fact, America is way ahead of Australia in this regard which I think is why the USA will develop the health card first. This year, franchised medical testing clinics are opening where anyone can go in and pay for any medical tests they want, with NO doctor's referral needed. If you think you want a particular test you just go and have it. A CT scan is about $US730. The patient gets back a full report. Then they can take that report to a doctor if needed. The high cost of medical treatment and medication in the USA means that there is much more financial incentive there for a smart health card development and use. Like most (all?) technology today, Australia will only get it as a spin-off from the USA.

Finally, let me say that the virtually free health system in Australia is about the best in the world, the above problems notwithstanding. (The baby-boomers like us will be kept alive from diseases which only 20 years ago would have killed us.)

I confidently expect to be running kitsrus.com for many years to come.

Peter Crowcroft PhD,
DIY Electronics (HK) Ltd,
Hong Kong.

Solar power bogged in bureaucracy

Of late, concerns have been expressed in several publications about the intrusion of the bureaucracy into every part of our lives. Now it appears that its clammy hand is touching those who have a hobby that is actually productive to society as well as being enjoyable; the electronic fiddlers! Although I have a degree in electronic and electrical engineering I take the title "fiddler" as honourable as the "rats of Tobruk" took theirs. Also, we know how hard it is to play a fiddle.

Being one of the first members of Greenpeace, I have seen with disgust how the bureaucracy has pulled the whole issue to the edge of imbecility with all the unrealistic and counterproductive rules. I live in the country and I see the effect on the farmers scratching a living. Putting my deeds where my words are, I designed and installed a solar/wind system 11 years ago, even though connection to the electricity grid would have been cheaper at the time.

Designed to, among other things, run a 100W computer it now runs two 350W+ computers (I also do programming as a hobby). Although the battery capacity is quite sufficient I wouldn't mind having another few solar panels. Thus I enquired about the solar rebate program that the Victorian State Government has in place at the moment.

However, the convoluted process of obtaining the rebate, together with the invasion of privacy, is worse than that to obtain a shooter's licence. And this last one is very obviously designed to keep you from having shooting as your chosen sport. Of course the bureaucrats expect you to use "SEIA (Aust) Accredited Renewal Energy Installers" and dare I mention it, the electricians also suitably stamped by the bureaucracy as experts. One look at the enclosed system planner will have you in stitches at first, but then you sadly ask yourself if this will ever be the clever country as long as this clammy hand tries to smother any free thought or enterprise.

In the "typical power" of the planner, a computer uses between 8W and 120W (most monitors has a 150-200W power supply but never mind), toasters 600W (slow toaster), etc. Every bathroom with a woman worth her hair has a hairdryer taking around 1000W but that is left out altogether.

Then, at the bottom of the page, is the biggest spark of brightness: "allowance for system losses: 50%", yes, fifty. If that doesn't put even the greenest conservationist off, I'll eat my hat. Maybe I am unbelievably clever that I have the most efficient system in the world but somehow by friends and I dismiss this possibility out of hand.

Needless to say, I am going to spend $2000 of my own money and not have bureaucrat-stamped experts snooping around my premises. Any electrician would be horrified to find that all the wiring is single conductor, 500mm apart, so low capacitance and low fire hazard. And how can no-earth be much safer than earths all over the place? No, I don't want the poor fellow spinning on his head.

It is a pity that the fiddlers have to go underground. Lucky fiddlers like Bell, Ericsson, Marconi and their likes lived in a different time, otherwise it would be a very dark and quiet world.

Politically incorrects will be tried on dark day, so please withhold my name if you publish this letter. Till that dark day I hope to continue enjoying SILICON CHIP.