This circuit appeared in Radio Elecronics magazine in 1968. The operating circuit is a general-purpose type at the time and the power supply must be symmetrical.
With the configuration shown in the figure, we have the relay being activated when the microphone picks...
We found this circuit in a 1992 Poptronics. What it does is to activate LEDs sequentially,...
In the figure we have an application of a voltage comparator in a circuit that fires with the...