The comparator In electronics, a comparator is a device which compares two voltage (less current) and returns a digital signal indicating which one is bigger. Elements of this type are often used in electronics, for example, to check if the input signal has a certain value. If input, the signal from the sensor a value of the comparator can act as a control system element. When you connect to one of the inputs of the comparator the signal from termoopornika, and the other reference voltage to obtain a simple thermostat. It is sufficient that the output plug control relay heater.