Temperature Sensor DIY for calculators

[Vtile]

Here is one example of using LM35 temperature sensor and I assume the AD and serial of the PIC to communicate with HP50g.

http://www.hpcalc.org/details/7306

You need basicly a four parts. A sensor, an amplifier, Analog to Digital converter, Serial link and calculator software.

I would personally use Pt100 or Pt1000 over NTC or PTC thermistors as they (PTs) are easier to handle with many magnitudes higher linearity. If LM35 style single chip devices can't handle the measurement environment (heat). The termocoubles introduces also complexity to the electronics as they need so called cold end compensation in another word they are measuring the temperature (in micro- and millivolts) differential between the cold and hot end of the thermocouble wire another thing with them is that they are far from linear.

As Platinum temperature resistors (pt100&pt1000) are almost linear by nature you might be good without even a linearisation in some cases. Pt100 is also defacto standard in industrial temperature measurement and been long enough that internet is floating with the amplifiers etc. analog circuit schematics to use. IIRC Burr-Brown (part of TI now) do have off the self pt100 bridge amplifier / transmitter chip. Pt1000 is easier as the ohms per Kelvin is bigger so you do not need as much accuracy (for amplifier) to your Wheatstone bridge or Kelvin sensing circuitry.