This audio frequency generator is a triggered signal generator. When a positive pulse of about 6 volts (minimum) is fed to the circuits input , a modulated audio signal comes out of the output. The signal pattern is similar to a bird’s chirp. The pulse width of the trigger signal must be a minimum of 2.5 miliseconds. The voltage supply is between 9 volts and 20 volts.
The circuit consumes about 2 mA or less. If the circuit is apllied as a morse code signal generator, replace C1 with a 0.1 μF capacitor.
Audio frequency generator circuit diagram
Audio generator PCB layout