We found this circuit in the October 1994 issue of Electronics Now magazine. The circuit uses a now-uncommon 4046 PLL and the gates of a CMOS 4001.
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...