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.
This relay circuit protects against accidental inversion of input polarity. The circuit was...
This 80's National Semiconductor circuit uses an era integrated circuit and symmetrical 5V power...
This circuit was obtained from Popular Electronics from March 1967. The transistor used is from...