Temperature sensing

I intend to place a few temperature sensors around my circuits to try to make calibration easier.

I've already bought an LM75AD that I intended to use for the VCO, that's an I2C device and can easily be put on the I2C bus I have on the Teensy.

For the filter modules I don't really want to put anything digital alongside the analog circuitry, so today I found a passive option - the MCP9700/9701, of which the MPC9700 is the cheaper and good enough. It's a simple device that outputs a voltage depending on the temperature and is built specifically for use with 8 or 12 bit ADCs.

The absolute accuracy is rather poor, but relative accuracy and hopefully repeatability is within 1degree C. As I don't need to know exactly what temperature we're at - I only need to store a lookup table for a few measured temperatures and interpolate between them, this should be good enough.

I will have three filters on the analog board, so being able to multiplex the voltage output to a single pin on the Teensy is a good idea. I was thinking that I could even combine it with the calibration input that is multiplexed from elsewhere in the analog circuit.

Here is a short example for how to connect it to an arduino:

https://startingelectronics.org/beginners/arduino-tutorial-for-beginners/measure-temperature-with-arduino-and-mcp9700/

And a note about how to increase the accuracy, though this is too complex to use I think

http://ww1.microchip.com/downloads/en/Appnotes/00001001C.pdf

Exponential converter heater

Just something I seem to search for over and over: An oven/heater circuit for keeping the exponential converter transistor pair at a constant temperature level to prevent detuning when temperature changes:

The minibrute. Uses ca3083, the microbrute uses lm3046 combined with ca3083 in a different combination as it also has a different expo converter. Expo pair is part of u10 (first two transistors).