This ingenious circuit was found in a 1990s Popular Electronics. The oscillator is a 555 and the keyer uses an optocoupler in the configuration shown.
We found this variable regulator circuit in a Radio Electronics issue from July 1984. It is one of...
The MC4741 consists of a quadruple 741. The power supply must be symmetrical, and the resistors must be...
Suggested by Sprague in the 1980s documentation, this circuit can control three-phase AC motors....