A quick look through a capacitor supplier's book shows that Polycarbonate and Dipped Polypropylene have pretty flat capacitance change vs temp curves in the region you are looking at. Polycarbonate caps should vary less than 1/2% over the -5 to 20C range. Polystyrene should be similar. Avoid ceramics with dielectrics such as x7r, y5v, z5U, and all electrolytics. Some of these can vary 40% over the temperature range you specified!!!! --Lawrence Lile ----- Original Message ----- From: "Gordon Williams" To: Sent: Wednesday, December 20, 2000 12:03 PM Subject: Re: [EE]: Thermistor temperature measurement > Hi Lawrence, > > Thanks for all your input. You have some good ideas that I will have to > think about. > It is a good idea to use caps for the PIC RC and measurement that are not > affected too much by temperature. What type do you suggest. These timing > and cap errors should be removed though (in theory) by doing a calibration > cycle using a known resistance just prior to doing a temperature > measurement. Do you have a suggestion for the type of resistor that I > should use for the reference resistance? I haven't looked to see if I could > find some temperature coefficients. In my mind this is going to be more > important as the temperature accuracy is only going to be as good as the > reference. > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.