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T.A. Babu

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In areas like staircase or porch of your own home, lighting is required just for a short time frame at night. We regularly forget to switch off these lights, which leads to considerable wastage of electricity. Here is an easy circuit that switches off the lights automatically after a predetermined time. The circuit consumes no power when inactive.

Circuit and dealing
Fig. 1 shows the circuit of staircase light controller. It consists of opto-isolator MOC3041 (IC1), popular timer NE555 (IC2), triac BT136 (TRIAC1) and a few discrete components. Timer IC2 is configured in monostable mode. Momentarily pushing switch S1 triggers the timer (IC2), which keeps the triac conducting and the sunshine bulb (B1) ‘onuntil the timer times out.

Producing a small DC voltage from AC mains to run an electronic control requires a step-down transformer or a voltage-dropping capacitor circuit. Here a tough and straightforward solution is adopted. Bulb B1 gets power via the diode of bridge rectifier BR1 and zener diode ZD1. The voltage drop across zener diode ZD1 is filtered by capacitor C1. This voltage is sufficient to run the remainder of the circuitry.

Working of the circuit is easy. Press switch S1 momentarily to turn bulb B1 ‘on.The bulb remains ‘onfor around 20 seconds after which turns off automatically. This duration is long enough for you to search out your way up or down the staircase at midnight. It might probably, however, be varied by changing the values of timing components R2 and C2.

Fig. 1: Circuit of staircase light controller

Construction and testing
An actual-size, single-side PCB for the staircase light controller is shown in Fig. 2 and its component layout in Fig. 3. Assemble the circuit on a PCB to minimise time and assembly errors. Carefully assemble the components and double-check for any overlooked error.

Fig. 2: An actual-size, single-side PCB for staircase light controller

Fig. 3: Component layout for the PCB

Switch S1 should have current rating corresponding to the load. Multiple switches will be installed in parallel to switch S1 to turn on the bulb from different places, say, from top and bottom of the steps. The circuit runs directly from mains power. So take utmost care while assembling.


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