MK138 Theremostat


I have the above kit, when the temp is below the setting the relay activates (shown by the led also) as the temp increases above the setting the relay deactivates and a fan is turned on using the NC contacts.

Is it possible to reverse when the relay activates, ie on when hot off when cold. problem I have is as my battery runs down, it drops so low the relay will no longer energize and it turns the fan on (draining further) regardless of the temp.

I have a low bat led circuit but the fan flattens the bat so much that circuit wont work either.

If you swap inverting (-) and non-inverting (+) op-amp inputs, it should work in the desired way.

all of them?

No, only the ones that are used as comparator to drive the relay.
(just in case: pin 12 & pin 13)

It worked, thanks :lol:

hi i really need to do this but i will be honest i don’t know what i am doing i don’t know what a comparator is so i don’t know what i have got to switch around any simplified information on this would be much appreciated. i have done so much searching and this is the only one i can find on this topic. many thanks

Just swap the pins 12 and 13.
For pin out info, please download the LM324 datasheet from the net.

Hallo folks,

I visited the site

And my questions were answered!!!

Thanks very much for your help!!!