First, I'm not an engineer, electrical or otherwise. And basic circuitry in undergrad physics years ago is the extent of my formal training in this area. Please be kind :)
I want to experiment with using a Type K thermocouple connected directly to GPIO pin(s) of a Raspberry Pi, using an RC(resistor-capacitor) charging circuit as outlined in this article: https://learn.adafruit.com/basic-resistor-sensor-reading-on-raspberry-pi?view=all
Instead of a photoresistor, I would use a thermocouple, of course. And I realize, too, as the article points out, that this is not as accurate as using an intermediary ADC (like MCP3008). But I'm curious to see just how (in)accurate such a simplified circuit would be.
I haven't put the circuit together yet, but I don't anticipate any problems with data acquisition. But the RC time equation (obviously) involves the relationship of resistance, capacitance and time. Not voltage. And the reference charts I've found for Type K thermocouple temperature conversion compare the temp to Volts, not Ohms.
And I'm not convinced the old standby V = IR would help here, because I don't think that I (current) is constant thru this circuit. If I'm wrong, I'd be happy to hear it - because then, whatever the current is, voltage and resistance would be proportional to one another. Then I could use an ice water bath for a 0 Celsius / 0 voltage reference point, and I could plot any other points based on the proportional rise. At worst, I'd probably need to take another reference reading (e.g. inside a pre-heated oven). But I'd like a simpler mathematical solution (i.e. convert voltage to resistance) which would allow me to use the existing charts, if I could.