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From: "Peter Nolan"
Subject: Book on Medical Electronics.
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Wed, 11 Dec 2002 12:38:20 -0000
NNTP-Posting-Date: Wed, 11 Dec 2002 12:37:40 GMT
Can you recommend a book on Medical Electronics? I have been in touch by
email with "It'shardtogetone" and he tells me he has basic
electronics(Re:Wanted:A device to meaure our brain activities). I hope you
don't mind if I ramble on a little because I too would be interested in
getting a book covering Medical Electronics. I'm sure I could find out this
for myself but if you happen to know of such a book I would like to hear
Over 20 years ago I built a sensitive thermometer as a Biofeedback monitor.
I used a 10k Thermistor in series with another 10k resistor and fed the
voltage across the resistor into the non-inverting input of a 353 op-amp
whose inverting input was biased in a way to maximise the sensitivity of the
circuit. The body's core temperature is 98.4 Fahrenheit(36.8 Centrigrade).
Doctors use the rectum to get a precise reading of this quantity. I'm sure
you have heard of rectal thermometers. Jay Leno(we get CNBC here) cracked a
joke about one not so long ago. To maximise the sensitivity of the device I
figured that the output from the 353 would start to go above 0V at say 25
degrees C and then swing up to the rail voltage(5V) at say just above core
body temperature. The reading on the four digit seven segment display for
the range would vary between zero and "9999". In this way I figured the
thermometer would be sensitive to .001 of a degree Centrigrade or
thereabouts and the reading while the thermistor was in a 1 litre beaker of
water was stable to within plus or minus one. Not bad.
The output from the 353 was fed into a 4046 PLL configured as as VCO and
frequency output was connected to a ZN1040E a Universal Counter/ Display
Circuit. I used a ZN1034E(no longer available) as a clock standard. The
counter counts for about a second when the count after that time is stored
and the counter reset. To do this a transistor(ZTX109) is used to introduce
a 10microsecond delay. I marvel at this ingenuity. There is a "Transfer
Input" output from the ZN1034E to the ZN1040E that is used to generate the
"Clear Input" so that the count over about a second can begin again. I'm
still impressed by this cleverness. I doubt if what I've just described well
but it's just the timing system to control the counter to act as a frequency
meter. The bit that excites me is the way a transistor was used to introduce
the delay needed.
I sold two units having built 10. Not a commercial success. Biofeedback
technology has moved on I suppose where the PC is being used as a data
acquisition system. I showed my device to the doctor running the Biofeedback
clinic in St. Vincent's Hospital(a general hospital) here in Dublin but
because the reading wasn't calibrated in degrees Fahrenheit or Centigrade he
wouldn't consider using the device so that was that.
I lifted the circuit for the VCO from a magazine I used to get on a monthly
basis called Elecronics Today International(ETI). I still have a stack of
them and built a drum machine and fuzz box using circuits from the same
magazine. The drum machine and fuzz box still work.
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