This circuit uses an LDR as a sensor to trigger an LED indicator at a preset lighting level. The power supply does not have to be symmetrical.
This small commercial radio for the MW band with germanium transistors was found in Japanese...
This alarm has a trip system with an LED on a keyring. The sensor is hidden by the glass or...
This circuit turns off when switch S1 is opened. The circuit is from the 1989 Radio Electronics...