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.
We found this circuit in a Radio Electronics. The circuit can be seen elsewhere on this site. The...
Found in old American documentation, this filter has a 8 dB per octave attenuation. The formulas for...
The circuit presented is from the Linear Applications Handbook of the National Semiconductor of...