temperature displays

I have a 7805 circuit built already to power the displays. it also has the caps to smooth out spikes. Done as provided by the fine people here. :)

So I already have that I can tap into, It will be powering both temp displays, and could probably power this new circuit I need to build.

I could not for the life of me ever figure out what parts I need to do what I want here, but if you guys know the parts needed I can buy'em and build it.

this is really low voltage too, 0.030v for 0*C, and around 0.017v for 24*c

When the voltage on pin 2 goes below the voltage on pin 3, the relay will energize.  I did not go back and see how your probe reacts to temp, nor did I go back and see if it is to trigger a fan at a high temp or a heater at low temp.  If it is backwards this way, simply reverse pins 2 and 3 of the diagram. 

The non positive wire of the probe should be already connected to ground inside the Temp Display.    Check that for me.  V1 is 12 volts to supply power to the circuit and power the relay.  Do not run 12 volts back into the display.  If I remember correctly, that is what this thread was started by. 

You have to leave the probe connected to the display.  Simply attach the wire from this circuit along with the probe wire.

You can use your present regulators.  There is minimal current draw from this circuit. 

No need to check the probe.  If the voltage is changing when referenced to actual ground.  This is what we need.

I changed the value of the resistor that connects to the 7805.  With the 1K resistor the control would be from 0 to (.)49 volts.  With the 10K resistor you will have much better control.