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.
With the values of the components indicated, this timer controls intervals from a few seconds to a...
This 80's circuit uses a light-sensitive SCR or LASCR and a one-sided silicon switch SUS, uncommon...
This circuit, found in ancient US documentation, allows you to switch the antenna from the...