Temperature Sensitive Audio Oscillator

This project demonstrates how Transistor collector current depends on temperature, by using the leakage current of a Transistor to control the frequency of an audio oscillator.

The 2SC Transistor is operated as a pulse-type oscillator. The bias voltage is controlled by the series circuit made up of the 22K Resistor and the resistance of the 2SA Transistor between C-E (collector-to-emitter).

This circuit is similar to the Electronic Thermometer see Transistor section. The base current and collector current of a Transistor vary with the temperature when you apply a specified base bias voltage to the Transistor.

Adjust the 50K Control so that the Speaker output is a low sound or pulses. Now warm up the 2SA Transistor by holding it between your fingers. You should hear the tone become higher as the Transistor temperature is increased.