This is a traditional 741 configuration with gain close to 100. We found it in the December 1972 Radio Electronics magazine. The power source must be dual.
With the configuration shown in the figure, we have the relay being activated when the microphone picks...
This Star Trek red alert circuit was found in the July 1990 issue of Radio Electronics magazine. The...
Found in a 90s American documentation, this circuit uses an integrated from the time that is...