Thermistor circuit with protection possible?

[PeterB]

When using an external thermistor, its possible it gets broken or unplugged. The standard voltage divider will result in the A0 pin rising to 3v3, which will blow the ESP8266.

Is it possible to make a circuit which will protect the ESP8266 in both the case of shorted and disconnected themistor?

[Jean-Marc Delaplace]

Yes, you insert between the center point of the divider and the A0 input a protection circuit.

Specifically:

Between the center point of the divider and the A0 input insert a 10 k resistor.

Between the center point of the divider and the +3.3V insert a schottky diode with the cathode connected to the +3.3V.

An example of such a diode is 1N5711.

The 10k resistor might cause a slight error in the measurement, but probably negligible.

[PeterB]

Thank you. I was trying to draw out the circuit you describe, then checking the board I see it already has a 220k and 100k bridge, so 'A0' can safely take 3v3.