Often, we forget to switch off some of the electrical devices in our houses and offices after their usage, especially those with short-duration requirements such as bathroom exhaust fans and lights. This leads to a waste of electricity and increased bills.
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 the 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.
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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 the EFY lab.
Interval Timer Circuit and Working
Fig. 2 shows the circuit diagram of the 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.