Toilet Lamp Controller

Many people forget to switch off lights, especially the toilet light at night. This results in wastage of electric power. Toilet Lamp Controller is specially designed to overcome this problem. After switching on the toilet lights, Toilet Lamp Controller automatically turns off the lights after a few minutes, which can be preset to individual requirements. You can set timing from 20 sec to 5 min.
About the Circuit :
Toilet Lamp Controller is built around the popular timer IC, used in monostable mode. For triggering in this mode, the IC requires a negative pulse, which brings the trigger input below 1/3Vcc. The normally low output then goes high for a period determined by the RC network comprising VR1, R1, and R2. The output pulse length is 1.1RC seconds approximately.
The tolerance of timing components makes it impossible to get highly accurate timing. This is overcome by the inclusion of potentiometer P1. The threshold voltage, which is 2/3Vcc can be raised or lowered to get accurate timing by P1.