per-el@obelix.liu.se (Per Elmdahl) (02/03/88)
Hello, world!\n A friend of mine wanted some advice, so I decided to ask the Net! My friend is attending a course where he is going to make an electronic construction. 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 :-) ) If you have any ideas about making such a device, please let me know via e-mail or on the net. -- / Per Elmdahl SM5OCI ( enea!liuida!obelix!per-el , per-el@obelix.liu.se )
larry@kitty.UUCP (Larry Lippman) (02/04/88)
In article <1434@obelix.liu.se>, per-el@obelix.liu.se (Per Elmdahl) writes: > My friend is attending a course where he is going to make an > electronic construction. 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. And y'all thought that tunnel diodes were dead... Consider using an FM transmitter operating in the 88-108 MHz region which is built around a tunnel diode (like a GE 1N3712 or equivalent). The power supply need be only a single 1.3 volt mercury hearing aid battery. With some clever design, the tunnel diode need be the only active component; a thermistor can be used to frequency modulate the transmitter signal. The resultant temperature-frequency function will be highly non-linear, but this is certainly no problem in this age of computer data reduction. Under the circumstances (snake in a captive environment), RF power in the hundreds of microwatts range is quite satisfactory - the tunnel diode will do this job nicely. There are a number of other circuit design possiblities, including those of totally passive devices - but the tunnel diode approach is the simplest to implement for this application. Incidently, during the latter 1950's when the tunnel diode was thought to revolutionize the semiconductor world, tunnel diodes were used in transmitter "medicine capsules" that medical researchers had people swallow to study human digestion in vivo. There were quite a few press releases about this application at the time. The transmitters primarily measured pressure or picked up digestive sounds; the latter application is subject to some amusing speculation... :-) <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
bill@sigma.UUCP (William Swan) (02/05/88)
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 :-)
max@trinity.uucp (Max Hauser) (02/05/88)
In article <2388@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: > ... >an FM transmitter operating in the 88-108 MHz region which is built around >a tunnel diode (like a GE 1N3712 or equivalent). The power supply need be >only a single 1.3 volt mercury hearing aid battery. I agree; I've built these, they're not difficult. The battery is the largest part. Use eighth-watt or smaller resistors if you use a voltage divider to bias the diode into its neg-R region. The neatest thing about the project, of course, if it's a snake of moderate size, will be tracking the transmitter visually from the outside ...
zahid@neptune.AMD.COM (Zahid Ahsanullah) (02/09/88)
In article <1434@obelix.liu.se> per-el@obelix.liu.se (Per Elmdahl) writes: > >Hello, world!\n > >A friend of mine wanted some advice, so I decided to ask the Net! > >My friend is attending a course where he is going to make an >electronic construction. 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 >-- > / Per Elmdahl SM5OCI ( enea!liuida!obelix!per-el , per-el@obelix.liu.se ) I don't know if this is going to be tiny enough but if he builds a bridge circuit with one of the arms of the bridge being a 1mm dia glass thermistor caliberated over the desired temperature range. He can then run the output through a voltage to frequency convertor which feeds a single transister (pnp) rf oscillator using the following specs on the tank circuit. 1000 Pf capitor in parallel with a coil made up of 30 turns of 25 SWG wire center tapped at 15 turns. This would give him a short range transmitter of maybe 100 ft if powered with 4.5 volts, transmitting at top band range. The transister used can be any low power oscillator (AF117 is a good one). The receiver should be capable of converting frequency to temperature. Circuits similar to the one I've described can be found in any electronics circuits manual type books. Have him look under microphone transmitters. Hope this helps him somewhat. regards Zahid
newsuser@LU.Se (Lund Institute of Technology news server) (02/12/88)
All this talk about small transmitters are interesting. Could anyone (L.Lippman?) give an example of a transmitter using tunnel diode? (Especially with some sort of modulation) (Or is that violating any laws to publish such a beast? :-) ============================================================================== Joergen Haegg jh@efd.lu.se EFD Lund Institute of Technology Sweden ==============================================================================