Beg Borrow or Steal a copy of the YSI catalog--all you ever wanted to know is in there--including a way to use two thermistors (e.g. 6K and 30K) to get very linear outputs. Really does work--we have an old signal conditioner product designed around this. Called "Thermlinear" by YSI. They even sell matched pairs with three leads. I think I've still got a few of the boards floating around--would be willing to sell, along with the schematics, for some nominal price each. Boards are about 2x3 inches and designed to plug into a passive back-plane or ribbon cable via a pair of 10-pin male headers. I'd have to go look, but I recall each card had two circuits on it. Really a neat system once you understand how it works, and figure out how to calculate the resistor values needed in the conditioner circuit. Designed for accuracies of 0.1% to .005% depending on the linear range selected. Only real draw-back is setting up the resistors--you need to be able to measure resistance to at least 0.05%--.01% or better is preferred, and have a wide enough selection to pull values off the shelf for each conditioner--otherwise its calculate, order, wait, measure, order, wait, etc. Boards are through-hole, and use standard 1/4 watt metal film resistors--usually read illy available. In our case, we needed a linear output around 39.5 DegC +/- 3 degrees, and ended up with a signal of 1 volt per degC, and were effectively measuring .001 degree resolution with a target 0.05% accuracy.. The system could be simplified quite a bit if lower accuracies are needed. Remember, most off the shelf thermistors are around 1% or worse anyway. Kelly At 12:55 PM 12/2/99 -0500, you wrote: >Not thaaaat simple. Resultant voltage in a resistor divider is not >thaaaat linear. >I made a computer program to search for the best *pseudo-linear* piece >of curve for a particular temperature range you need, based on a >resistor division combination. I will dig it and email to you directly. >Wagner > >> Ercan Duran wrote: >> >> Hello. >> >> I'm trying to use a NTC thermistor with a 16F877 device. >> It's a 10K thermistor B Constant 25/50 C(K) = 4100. >> If I read resistant of the NTC, how can I calculate temperature in >> Celcius degree.? >> >> Thanks in advance. >> >> Ercan DURAN > > William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems & San Diego, California, USA