temperature control circuit

Thread Starter


Joined Dec 21, 2005
Hi there

I currently have a temperature control circuit http://www.quasarelectronics.com/1048.htm which has a temperature range of +20 to 70 degrees, however I am looking at adapting it so that the relay can switch when the temperature gets in a range of around 2-8 degrees.
Is it just a case of changing the potentiometer, i currently have replaced it with a 4k7 which seemed to do something but i couldnt quite get the relay to switch correctly.

I would appreciate any help.
Many thanks


Joined Jan 10, 2006
Your link doesn't contain a circuit diagram, just some sales/product blurb.
Without seeing how the circuit works it's hard to say.
If its Microprocessor based, then it would probably mean reprogramming the micro (if it has a digital display then this will be the case).

If its "Comparator" based..(my guess from the picture), then you may find that the Potentiometer is part of a divider, and probably has a resistor from one end of the pot going to earth, and from the other going to a voltage reference, with the wiper going to one of the comparator inputs.
The sensor would be part of another divider or reference that would be applied to the other input of the comparator
In this case, to change the range you would alter the values of the resistors around the pot while trying to keep the total resistance of the divider close to the original... effectively changing the pots posistion in the divider.
The exact details can't be known without a circuit diagram and more info.

Of course it might still be digital even without a digital display, in which case the sensor goes to an input of the micro, the pot goes to another, and a program runs which compares the values and takes the appropriate actions. Not much you can do about that without rewriting the program and reprogramming another microcontroller.