Wednesday, January 18, 2017

Jim’s Temperature Controller

The purpose of this device is to regulate some item like a fan or a heater by temperature accurately. The Digital Thermostat circuit board is available from Marlin P. Jones ( for about $5. (Part #32184-MP) They would also have the wall-wart power supply with an output of anywhere between 14.5 to 27vdc.

In this circuit I used a 20 amp relay that was re-used from an old hot tub controller. The standard outlet is modified by breaking the hot connection between the two outlets so that the one outlet is hot all the time for the wall-wart and the other outlet is hot when the circuit board commands.

This Digital Thermostat circuit board should be extremely accurate. One can purchase either the Centigrade or Fahrenheit model. There is a probe that comes with the board which is attached to about a foot length of wire. The board has an accuracy of 0.1 degree Centigrade and can control with just a 0.1 degree of change. It can be configure to energize the relay if it either gets too cold or too hot. The board has memory even after power is removed so that one does not need to reset after power is reapplied.

Completed project
Relay on right side

Digital Thermostat board

Power on 

Temperature probe