This is aquiz bell/alarm circuit. This circuit indicate “fastest finger first”. This circuit has one bulb for Quiz master and one for each contestant. The bulb will illuminate when a button is pressed. the cathode of the 9v1 zener sees approx mid-rail voltage. The Quiz Master bulb is also illuminated. Here is the circuit:
There is no other bulbs can be lit until the circuit is reset because The zener comes out of conduction and no voltage appears across the 120R resistor. The reset switch must be a normally closed push button, to disconnect the power supply when it’s being pressed.
