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.
B In this circuit we show how to use an electret microphone powered by a small battery (can be of...
This circuit is from a 1976l filter cookbook. The circuit has a factor Q = 3, and must be supplied...
Using transistors at the time, this circuit was found in a 1970s documentation. Transistors support...