This circuit was found in a Popular Electronics from the 90s. The circuit uses common components today. The waveform of the generated signal is shown next to the diagram.
With the configuration shown in the figure, we have the relay being activated when the microphone picks...
This TTL generator that can function as a control shield or external clock for microcontrollers was found in...
The OP07 operational amplifier is not common today, as the circuit is from an old European manual....