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 circuit was found in a 1986 publication. However, it can still be easily assembled, as the...
In the figure we have an anti-ring circuit with 4093. The duration of the pulse is given by R1 and...
This circuit was originally indicated to generate audio signal for analog TV sound. The circuit is from...