Experiment 13 - The Staircase Light Circuit

You surely known the functionality of a stairway lighting system. If no one is in the staircase, the emergency lights are on. If you press the light switch the staircase lights go on. After a while the lights go off again and the emergency lights on.

Staircase Light Circuit. (Enlarge)

Consider the circuit shown. When you connect the battery, the "emergency light" LED2 lights up. If you press the "light switch" S1, the "emergency light" goes out and the "stair case light" LED1 lights up. With a delay of several seconds the "stair case light" LED1 goes out without any external influence and the LED2 lights up again. Again you can try to influence the delay times using the capacitor C1 and resistor R2. They constitute in this experiment, the RC circuit.

Circuit diagram of a staircase light circuit.

How the circuit works in detail cannot be explained at this point. For more information have a look at the topic about multivibrators, as this circuit is a monostable multivibrator.

In the next experiment, you expand the circuit by another RC circuit and in turn obtain another well-known application.