It uses a negative temperature coefficient thermistor for temperature sensing element Rt. By the resistor Ri, Rs, , potentiometer RP and thermistor R. Composition temperature bridge; by the transistor VTi, VT2 constituting the differential amplifier; by the transistor and diode
VD composition VTs output circuit; by the transistor VT4, VTs and capacitor C etc. audio oscillator. Adjustment potentiometer RP, can change the temperature setting.