The nightlight is a popular project in schools and, depending on the circuit used, suitable for a very wide student age range. Even at key stage 2, students can learn much from a basic circuit comprising a battery, switch and LED. More sophisticated automatic PIC or RC timer controlled circuits offer the scope for programming or investigation of resistor and capacitor values and can form the basis for product design at ‘A’ level. Battery powered nightlight circuits however, have the downside that they contribute to the global mountain of discarded batteries. This includes the nightlight project I describe elsewhere in ECT Education.
One day, one of my year 8 students suggested that our night light project would be better if it could be solar charged instead of relying on batteries. Since the circuit was controlled by ambient light level, it seemed logical to her that it should also be re-charged by light. On the surface this seemed like a great idea but the problem is solar cells only produce 0.5V in strong light so 8 cells would be needed in series to generate an operating voltage of 4V (to drive white LEDs) for battery charging.
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