Here is a reliable, low power, versatile and simple to wire automatic bathroom light off timer. It is built around NE555 timer which will turn off the light after a preset time. Main advantages of this circuit are-
1. When there is no one in the bathroom it will automatically off the light after preset time, thus saving electricity.
2. Once timer switches off it will not reset automatically until we supply power.
3. Consume no current in standby mode therefore longer battery life.
4. Provide facility to set time according to the requirement.
5. Easy to mount because of less components used in circuit.
Fig. 1: Prototype Of Bathroom Light Off Timer Circuit On Breadboard
In this circuit 555 timer is wired as one shot timer whose timer period can be easily calculated by-
Where T is in seconds, R is in ohms and C is in farads.
When anybody wants to use the bathroom, it will press the switch momentarily. As soon as switch is pressed, relay connected to pin 3 of IC1 gets energized and switches “on” the light connected to the relay. After the pre set time, the output of timer will go low and de energizes the relay, thus switching “off” the load connected to the relay. In this circuit you can adjust the time with the help of VR1 and calculate the time period from the above formula.
One must take care of specification of relay before mounting like how much load current it will support. It is always suggested to keep the relay coil current within 200mA. If you want to exceed the coil current one must use driver transistor to drive the relay.