This circuit was found in a Popular Electronics from the 90s. The power source must be symmetrical and the operational amplifiers can be 741.
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...