Found in a 1964 Electronic Design this circuit compares two signals by providing the inverse of the algebraic sum of their frequencies. The circuit can be made with modern equivalent transistors.
This 2004 circuit is based on the ionization effect that occurs in old incandescent lamps with...
This bidirectional current sensing circuit was found in a 2005 Linear Technology application manual....
This circuit can be used in decoration or to draw attention, in a “fake” assembly for example. What he...