Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!nrl-cmf!cmcl2!husc6!mit-eddie!uw-beaver!tikal!sigma!bill
From: bill@sigma.UUCP (William Swan)
Newsgroups: sci.electronics
Subject: Re: Extremely small transmitter - help!
Message-ID: <1473@sigma.UUCP>
Date: 4 Feb 88 17:18:58 GMT
References: <1434@obelix.liu.se>
Reply-To: bill@sigma.UUCP (William Swan)
Organization: Summation Inc, Kirkland WA
Lines: 30

In article <1434@obelix.liu.se> per-el@obelix.liu.se (Per Elmdahl) writes:
>His project consists of constructing 
>and building a tiny transmitter for measuring the temperature
>in the stomach of a snake! (Can you believe it?). Now he is 
>wondering about how to make such a small tranmitter, how to
>power it, and how to make an antenna. (Please no jokes about
>half-wave snakes :-) )

About 20 years ago (sometime from January 1967 to May 1968) Scientific
American had a construction article (in a regular column called, I think,
The Amateur Scientist?) for just such a beastie. Memory says it was nothing
more than a small one-germanium-transistor RF oscillator operating in the
AM broadcast radio band (540-1600 KHz). 

I don't recall exactly how temperature measurement was performed - but I
think that the transmitting frequency was a function of temperature. The
author calibrated his device before feeding it to his dog, and used it to
measure the temperature through the canine's tract - until one day he quit 
receiving signals from it. I think I hardly need say why (nor how and where
he finally found the device! :-)

I built a couple of these devices, but as a poverty-stricken teenager had
to use parts on hand. Still, they ended up being about half the size of your
thumb, battery included, so I know they could be made much smaller. They had
a useful range, with my insensitive two-transistor radio, of a couple feet.
(And no, Bosco and Mani were never fed one.)


-- 
William Swan  {ihnp4,decvax,allegra,...}!uw-beaver!tikal!sigma!bill
-The Society for the Preservation of the 1979 Book of Common Prayer  :-)