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What's the best place to apply heat (or cold) to a bimetallic strip for the greatest effect?

Erm... ok...

I’m wondering, theoretically, if you use NTC thermistors and have them cooled down, wouldn’t the resistance increase? Since the resistance reduces when heated up, I think it makes sense...

Shr3D wrote:Erm... ok...

I’m wondering, theoretically, if you use NTC thermistors and have them cooled down, wouldn’t the resistance increase? Since the resistance reduces when heated up, I think it makes sense...

That does make sense because it is correct. There are a number of ways you could use an increase in resistance to trigger another task.

CookiePie1 wrote:

Shr3D wrote:Erm... ok...

I’m wondering, theoretically, if you use NTC thermistors and have them cooled down, wouldn’t the resistance increase? Since the resistance reduces when heated up, I think it makes sense...

That does make sense because it is correct. There are a number of ways you could use an increase in resistance to trigger another task.

One way I didn't realize until this morning is an NC relay. Once the resistance goes over a certain level, the current should drop, meaning the electromagnet inside the relay would switch on, and you could then do a thing. (that thing being the next task of course.)

PM2017 wrote:

CookiePie1 wrote:

Shr3D wrote:Erm... ok...

I’m wondering, theoretically, if you use NTC thermistors and have them cooled down, wouldn’t the resistance increase? Since the resistance reduces when heated up, I think it makes sense...

That does make sense because it is correct. There are a number of ways you could use an increase in resistance to trigger another task.

One way I didn't realize until this morning is an NC relay. Once the resistance goes over a certain level, the current should drop, meaning the electromagnet inside the relay would switch on, and you could then do a thing. (that thing being the next task of course.)

Hmm ok... but are NC relays non-programmable? And could you attach a link to one?

I am waiting on the last part in the mail, but am just curious (so I know if I really need to adjust anything while I wait a week for shipping), how long does this action usually take?
I plan on using a peltier cooler and a thermistor.

C8H10N4O2! wrote:I am waiting on the last part in the mail, but am just curious (so I know if I really need to adjust anything while I wait a week for shipping), how long does this action usually take?
I plan on using a peltier cooler and a thermistor.

There is not set amount of time, it depends on the difference in resistance between your thermistor and whatever other source of resistance you have in your circuit, be it a fixed resistor or potentiometer. If the difference was greater, it would take more time, and vice versa. As we have it set up, it takes about half a second.

We're trying to use a peltier cooler and thermistor in a circuit like the one attached, but we're having problems with calibrating the switching temperature. Is anyone else using something similar and have you had problems with re-calibrating at competition?

ftf841 wrote:We're trying to use a peltier cooler and thermistor in a circuit like the one attached, but we're having problems with calibrating the switching temperature. Is anyone else using something similar and have you had problems with re-calibrating at competition?

Two things:

1. Instead of your 50k bias resistor, consider using a thermistor (identical to your 100k thermistor) as the bias resistor so that you don’t have to recalibrate for room temperature.

2. Keep in mind that an LM393 can only sink 1mA per the datasheet — consider having a higher value resistor for the LED to avoid reaching this limit. Alternatively, amplify the output with a PNP transistor.

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