ANALOG TIMING LIGHT PROJECT CIRCUIT DIAGRAM
Analog Timing Light Project
This analog timing light project uses RC circuit as a delay OFF timer to control the duration an incandescent light turns ON. When the accuracy of a timer is not critical, the use of RC circuit is a good choice as it is more cost effective and simple.
Once the normally open switch SW is pressed, the light will turn ON for a duration of 10 - 20 seconds before it turns OFF. The duration of the turn ON time can be varied by varying the values of R1, R2 and E1.
The schematic of the project is as shown below.
Once SW is released, E1 will discharged through resistor R2 and the base of the transistor. After some time, When the voltage across E1 drops to approximately 0.5V, the transistor will turn OFF. This in turn will cause the relay to turn OFF and the incandescent light will turn OFF. The timing of the turn OFF can be changed by changing the values of E1, R1 and R2.