This circuit for frequencies of 20 to 2 kHz was obtained in English documentation from 1966. The transistor can be any general purpose and powered by batteries.
This circuit was found in an American publication from 1965. The circuit uses components from that...
This circuit prevents damage by accidentally reversing the power supply polarity. The circuit is...
A square signal of about 1 kHz is produced by this astable multivibrator. Frequency is determined...