Need help.

Question

Hi all.

I need your help. I am building a thermostat that has a fan. The fan starts working when the temprature is too high as well as a red led lights. The problem is that when the red led lights the temprature increases a lot. Why that happens?

Robert Peter Oakes · Accepted Answer

what do you think you need it for ?? What i mean more generically is provide a description of the project, what are you trying to do, obviously there is a HIGH, Medium, Low temp LEDs to indicate a status, the temp sensor to read a remote temp, a fan to cool what ??, I was assuming you where using the motor to simply emulate a fan (You don't have a fan available) and the speaker to produce an audible alarm of sorts. ?

johnbeetem · Answer

It would help if we could see a schematic to see how you are driving the LED. Do you have a current-limiting resistor in series with the LED? If you don't, the transistor driving the LED can get very hot and may fail. If the transistor is inside a microcontroller, that microcontroller will get hot and may fail. Typical current-limiting resistor value is 200-1000 Ohms, depending on how bright you want your LED.

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