We found this circuit in a French documentation from the 80's. The components used are still common and the circuit can generate signals from 10 Hz to 100 kHz.
This circuit was obtained from the CA3140 datasheet. This component consists of an operational amplifier...
In the figure we have one of the many options found in this section for an intercom using ordinary...
Found in Electronics Now from the 90s, this circuit can use any general-purpose transistor. The power...