INTERVAL TIMER

Often, we forget to switch off some of the electrical loads/ devices in our houses/offices after their usage, especially those with short duration requirements such as bathroom/toilet exhaust fans and lights. This leads to wastage of electricity and increased bills.

- P. Balasubramanian

To overcome this problem, we present a simple interval timer circuit. When this circuit is connected between the power supply and the load, it automatically switches off power supply to the load after a preset time (in this case 15 minutes). This ensures that the devices are used only for the necessary amount of time, resulting in energy savings.

To switch on the device again, one must switch off the circuit and then switch it on to get another preset time usage. Fig. 1 shows the prototype tested in EFY lab.

Circuit and working

Fig. 2 shows the circuit diagram of interval timer. It is built around a 230V AC primary to 12V, 1A secondary transformer (X1), five 1N4007 rectifier diodes (D1 through D5), CD4541BE (IC1), 12V voltage regulator LM7812 (IC2), npn relay driver transistor 2N2219 (T1), a 12V one changeover relay (RL1), and a few other components.