Feb 3, 2013

Simple Key-Hole Lighting Device

When opening the door of your room in the dark, you may have to spend a few minutes searching for the key-hole. Here is the circuit of a lighting device that makes it easy for you to open the door in the dark. An ultra-bright red LED in this circuit flashes rather than lighting continuously.

This simple circuit is an extracted circuit board from a discarded quartz timepiece. Most hobbyists might be having one such unit in their junk box. First, disconnect the coil and its fittings, noting the pads that it is connected to. The other components can then be connected across the pads as shown in the circuit diagrams. There are two circuits: manual (shown in Fig. 1) and automatic (shown in Fig. 2).
Fig. 1: Simple key-hole lighting device (manual)
Fig. 2: Circuit for key-hole lighting device (automatic)
The circuit (Fig. 1) is powered from a couple of AA cells. Whenever the door is closed, a piece of magnet mounted in the door frame comes close to the reed switch and powers the circuit. When the circuit is powered, LED1 flashes every two seconds. An on/off switch is provided to switch off the unit when it is not required.
Fig. 3: Door assembly
 As shown in Fig. 2, photo-transistor L14F1 (T1) is added to refrain LED1 from flashing during day time (when there is sufficient light). An on/off switch is provided to switch off the unit when  it is not required. This circuit design, if properly mounted, will decorate your door at an amazing low assembling cost. After proper fabrication, fix the complete gadget above your door lock as shown in Fig. 3.

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