Found in an American 1980s documentation, this circuit compares signals from two TTL sources, providing an output that depends on the frequency difference. The circuit can be used as a shield.
This 1995 circuit uses an audio amplifier that is no longer common today. However, other...
The tone produced by this circuit attract fishes. The circuit is installed into a small can and...
This circuit is from Mullard 1969 documentation. The circuit operates at a relatively high supply...