Teensy 3.2 with Thermocouple or RTD

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frabulus

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Has anyone used the Teensy 3.2 for temperature measurement directly with either a thermocouple or RTD?

I could use break out boards, but the 3.2 has a very nice programmable gain ADC and I would like to put it to use.

There are two options for slightly different purposes:
1) Thermocouples have the advantage of a very small sensor and no self heating. https://www.ti.com/lit/sbaa274 is a good guide to thermocouples measurement and the circuit on page 17 seems the simplest. Any suggestions on the resistor values for bias and ADC input? I would also have to measure the temperature at the Teensy. I'm shooting for +/- 2°C accuracy.

2) An RTD (aka pt100) is more accurate but larger. Self heating is an issue but it is connected to a large copper block. After reading omega.com, the plan is to put 1 mA though the RTD with a stable resistor in series. E.g. a 1 k resistor in series and connect to AREF. Can the AREF provide 1 mA and still be stable? The voltage at the RTD would be 100/(1k + 100) * AREF = 0.1 V. Should be possible to measure the voltage accurate enough to give a few tenths of a degree accuracy.

My work (solar cells) is DC with sample times of seconds so I can do a lot of averaging. The RC time constant of the ADC is ~10 ns so irrelevant for my application.

I use DS1820 for temperature but TC and RTDs have certain advantages.

I realise using the Teensy ADC is kinda nuts when compared to add on boards. Is it slightly nuts or totally nuts?
 
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