Jim Jackson  wrote:
> The setup you describe provides a variable analog voltage output. Non of
> the raspberry pi have the capability to directly read an analog voltage,
> you need an add-on Analog-to-Digital-Converter (ADC) either as a "hat",
> breakout board, or chip in a breadboard.

You don't need an ADC, you can do it via timing a capacitor.

Wire up something like this:

GPIO0 -=thermistor=-----+---||----- GND
            R           |    C
                      GPIO1

Set GPIO0 low, wait a while.
Now set GPIO0 high and start timing
When GPIO1 goes from 0 to 1, stop the clock

If you know the time, capacitance C, the GPIO output high voltage, and the
low-to-high threshold voltage for GPIO inputs, you can solve the capacitor
charging equation to find R.

Putting the midpoint into a comparator with a more precise threshold would
help with accuracy over using GPIO1 directly.  Using its reference voltage
as GPIO0 divided exactly in half via a potential divider would make the
system independent of I/O voltage variations.

Theo

--- SoupGate-Win32 v1.05