Sound Generation using 555

The task of this sound generator circuit is to give a frequency output which lies in the audible range of a human being, i.e in between 20 and 20,000Hz. Sound is generated in this circuit by using two 555 timer IC’s. The other components required in this project, along with the two ICs are few resistors and capacitors, one diode, 12 Volts DC power supply, and a speaker. The loudness of the speaker can be varied by using power amplifier at the output stage. Image below details with the internal circuitry of one such 555 IC. Can you look at the IC and tell how does the circuit works?

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Fig. 1: Circuit Diagram For 555 IC Internal Circuitry

In this sound generator circuit both the ICs are wired as astable multivibrator. Both the 555 timers operate at different frequency ranges. IC1 works at a frequency of about 20Hz as a slow astable multivibrator with duty cycle of 50%. IC2 operates at a frequency of 600Hz as a fast astable multivibrator.

When power is supplied to the circuit, output of IC1 becomes high. Then it is fed to the control pin (pin5) of IC2. With this connection, the output frequency of IC2 becomes modulated with the output frequency of IC1. The frequency of the second oscillator rises and falls with the voltage shift on pin 5.

The power supply to the sound generation circuit can range from 6V to 15V and here in this circuit power supply used is 12V DC supply. By inserting a power amplifier circuit at the output stage the loudness of output can be further increased.