Thermistors for Thermostats - Bonus Blog Post

RE: Thermistors for Thermostats - Bonus Blog Post

DAB — Tue, 20 Sep 2022 20:03:30 GMT

It is always interesting when you use analog components in a digital control circuit.

Those pesky transitions seem to move around a little.

You might have better luck with a comparator circuit to reduce the hysteresis.

RE: Thermistors for Thermostats - Bonus Blog Post

scottiebabe — Tue, 20 Sep 2022 13:24:06 GMT

Using the thermistor in a bridge configuration make life easy! For some critical temperature you either look up or calculate the thermistors resistance. Then create a second voltage divider using that fixed value.

The polarity of the bridge output will switch at the critical temperature regardless of the magnitude of the supply voltage.

Then with an op-amp with a little positive feedback for hysteresis you have a solid-state thermal switch. Yay!

I'm envious of your hummingbirds having a sous-vide buffet all winter long [emoticon:c4563cd7d5574777a71c318021cbbcc8]

Great experiments!

RE: Thermistors for Thermostats - Bonus Blog Post

rsjawale24 — Tue, 20 Sep 2022 04:47:06 GMT

Hey! Great idea. I have used an opamp to realise the same circuit that you are trying to achieve. You can set the trigger point and sensitivity using a potentiometer.

I'm using a voltage divider for setting the reference voltage however the voltage divider using resistors is not a good implementation because the resistance tends to vary as the resistor heat up due to current flow and this will change the reference voltage.

Another method to set a fixed voltage reference is to use a zener diode or best possible method is to use a bandgap voltage reference. There are many ICs available for this and a bandgap voltage reference is temperature independent!