This circuit will control a heat source such as a heating mat or a high wattage bulb for an incubator or seed propagator.
The heat source should be central to the incubator or environment it is heating, and the sensor near the edge.
The temperature can be controlled by VR1 on the Comparator Switch.
There are 2 versions of the circuit shown below.
Circuit Voltage: 6 to 9 volts
Heater Voltage: as required
Adjust VR1 with a screwdriver to the centre position.
If the temperature you require is outside the range of VR1 on the Comparator Switch, then adjust VR1 on the Heat Sensor.
The Schmitt setting should be selected by moving the jumper to the right, creating hysterisis in the switching.