We found this circuit in the November 1984 Radio Electronics magazine. The base frequency is given by C1. The power supply can be between 3 and 12 V.
This circuit using an operational amplifier was found in old American documentation. It can be...
If the circuit oscillates, emitting sound, it is because the transistor is good. This simple...
Like the previous circuit, this is used in the analog part of the telephone lines. The same...