The indicator for this circuit is a 0 to 1 mA milliammeter. The operational is from the 70s, when the circuit was published. Modern equivalent can be used.
This circuit works both as a preamplifier and activates a relay when speaking in front of the...
This simple CMOS touch switch with bistable action must not be powered by a source without a...
This circuit activates an incandescent lamp (it cannot be of another type) when it gets dark. The...