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 circuit shown is suggested by National Semiconductor in its 1994 Linear Applications Handbook. We...
The ZN416E integrated circuit is uncommon today. It consists of a complete radio, like the one...
In the figure we show how to implement a voltage reference with the ON Semiconductor rail-to-rail...