Often streetlights remain on till late in the morning and are not switched on as soon as it gets dark. This circuit will automatically turn off a streetlight at dawn every morning and switch it on again at dusk each evening. The author’s prototype is shown in Fig. 1 while its circuit diagram is shown in Fig. 2.
The circuit has a step-down transformer (X1), a bridge rectifier (BR1), 12V voltage regulator 7812 (IC1), op-amp LM741(IC2), a 12V single-changeover relay (RL1), and a few other components. Capacitor C1 connected across the supply terminals minimises ripples and any other noise signals.
The circuit works on 12V DC, which is obtained from the 230V AC primary to 15V, 500mA step-down transformer X1. The 230V AC mains is connected to the primary of X1 via CON1 in the circuit. The transformer’s 15V AC secondary is connected to bridge rectifier BR1 for rectification of the voltage, which is filtered by capacitor C1. The rectified and filtered voltage goes to IC LM7812 to get regulated 12V DC voltage for the circuit.