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.
The timing steps of this circuit are indicated by a 7-segment display. The circuit was found in...
We found this circuit in a 90s Radio Electronics. The secondary current of the 110 or 220 V...
We found this circuit in a book on espionage from the 90s. The circuit has a counterphase...