During an unexpected blackout in particular, a simple light source can be a handy aid. With only two transistors, one photo resistor, and a few other components you can build an automatic emergency light. Here’s the circuit of my recently built, battery operated, little rescue light that lights up automatically in dark times!
Circuit Diagram
Component List
- R1: 1K
- R2: 10K
- R3: 100Ω
- T1,T2: BC547
- LDR: 5mm type (>100K @ dark)
- LED1: 3mm White (3.4V/50mA)
- S1: SPDT Slide Switch
- BAT: 6F22 9V Battery
Construction Note
As you might noticed, the circuit is extremely simple and hence can easily be wired on a very small piece of perf-board. The author, however, used the good old point-to-point wiring method to fit the whole electronics inside the shell of a defunct night lamp’s enclosure (get it done anyway you can). Following is an inside view of author’s quick prototype.
Final Touch
Since the circuit is powered from a 9V battery, it’s easy to add two white LEDs in series instead of the single one. If so try to alter the value of current limiter resistor R3 using theoretical and/or empirical methods. Similarly you may need to change the value of R1 up/down to fine-tune the detection sensitivity of the ambient light sensor wired around the photo resistor. That’s all for now, folks!
