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 is the traditional configuration of na Astable Multivibrator using two NPN ttransistor....
This treble and bass control drains some milliamperes from a 12 V supply and can be used with any...
This is a very simple configuration with a power transistor to control a DC motor from 3 to 12 V...