Found in a Popular Electronics from the 9s, this circuit has output for RS-232 interfaces and current input. The power supply must be symmetrical.
This encoded lock circuit with alarm for use in homes was found in a publication from the 90s. The...
This old circuit, from a 1992 documentation, was used with tape recorders acting as playback. The...
This circuit was found in a 1968 Motorola documentation. The circuit can be implemented with...