With the configuration shown in the figure, we have the relay being activated when the microphone picks up a sound and shutdown when the X1 reset sensor is activated.
This is a Japanese commercial circuit found in a 1967 documentation. The transistors are from the...
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...
This control of DC motors for currents up to about 200 mA was obtained in an American publication of...