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 solid-state relay (SSR) or shield was found in a 1995 Electronics Now. The transistor can be...
The components used in this National Semiconductor circuit are not common today, but the...
The circuit presented in the figure is an amplifier for stereo sources with the Maxim MAX9723...