Post by thread:Thermistor Questions

Hello everyone! I'm currently in the need of a PIC16F84 circuit that would analyse the temperature of an ice cube I have in my freezer. :) I was thinking of a thermistor allong with a 10 or 12 bit A/D converter. Would that make sense? The problem is, do you think I could place the thermistor in the water? Most of the time the water will be in a solid form but it could possibly turn liquid depending on the temperture conditions. So would the thermistor still work? Will it do the job? Or...? Also, where can I get more information on interfacing the '84 with an A/D? Thank you! Jean-Francois

Jean-Francois ou Alain Joly wrote: > I was thinking of a thermistor allong with a 10 or 12 bit A/D > converter. Would that make sense? Not to me. I would use the cheapest design in terms of actual hardware connections, which for me would be a PIC connected to a DS1820 temperature sensor chip. -- James Cameron (spam_OUTjames.cameronTakeThisOuTdigital.com) Digital Equipment Corporation (Australia) Pty. Ltd. A.C.N. 000 446 800

Hi, good news for you. There is the AN512 (maybe AN513) describing how to measure resistance with a PIC w/o A/D converter. Depending on speed, you can increase resolution. I tried it and it works fine! The thermistor wires you can put in a plastic thin tube after making a soldered connection, then pour some arteficial resin (I hope it can be understood; I translated it from German: "gie§ etwas kŸnsliches Harz in die Schlauche"). It should give enough protection. Imre

Epoxy potting the thermistor is good <G> (That's what the Dr. was trying to say, I think.) Leave the tip of the thermistor close to the surface of the epoxy, or even out of the epoxy... One project I was in, we ended up cutting slits into a polyurethane wire bundle (16 or 20 pairs, one slit per pair to measure temp's at different depths), fishing out the individual twisted pair of wires, and soldering a thermistor across each pair, then epoxy potting the whole mess inside of a 35mm film container to seal it. Worked pretty well! Mark, .....mwillisKILLspam@spam@nwlink.com Dr. Imre Bartfai wrote: {Quote hidden}> > Hi, > good news for you. > > There is the AN512 (maybe AN513) describing how to measure resistance with > a PIC w/o A/D converter. Depending on speed, you can increase resolution. > I tried it and it works fine! > > The thermistor wires you can put in a plastic thin tube after making a > soldered connection, then pour some arteficial resin (I hope it can be > understood; I translated it from German: "gie§ etwas kŸnsliches Harz in > die Schlauche"). It should give enough protection. > > Imre

>The thermistor wires you can put in a plastic thin tube after making a >soldered connection, then pour some arteficial resin (I hope it can be >understood; I translated it from German: "gie§ etwas kŸnsliches Harz in >die Schlauche"). It should give enough protection. Good enough translation! Basically, use a thin-walled tubing of a thermally-conductive nature, fill with a non-thermal-insulating potting compound (or ceramic). The idea is to keep the wires from breaking but also to transmit the heat. Andy ================================================================== Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA ==================================================================

Jean-Francois ou Alain Joly wrote: > Hello everyone! I'm currently in the need of a PIC16F84 circuit that > would analyse the temperature of an ice cube I have in my freezer. This is similar to the oven controllers I design. I use a thin piece of teflon heat shrink tubing to isolate the theristor from the outside world. You could probably use standard heat shrink at these low temperatures. > :) I was thinking of a thermistor allong with a 10 or 12 bit A/D > converter. Would that make sense? How much resolution do you need? I use the A/D inputs on a 16C620, only good to 4 bits, to do a whole oven controller. Other PIC parts will give you 8 bit resolution. How much range and how small an increment do you want to measure? -- Lawrence Lile "An Engineer is simply a machine for turning coffee into assembler code." Download AutoCad blocks for electrical drafting at: http://members.sockets.net/~llile/index.htm

>>The thermistor wires you can put in a plastic thin tube after making a >>soldered connection, then pour some arteficial resin (I hope it can be >>understood; I translated it from German: "gie§ etwas kŸnsliches Harz in >>die Schlauche"). It should give enough protection. > >Good enough translation! Basically, use a thin-walled tubing of a >thermally-conductive nature, fill with a non-thermal-insulating potting >compound (or ceramic). The idea is to keep the wires from breaking but >also to transmit the heat. > If you can tolerate a little more thermal inertia, use the sort of shrink tubing that has an adhesive liner. This will seal the thermistor and wires into a monolithic assembly in one easy step. Reg Neale