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how to make rechargeable led light when power fails? Answered


Tags:light

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Here's what I'm thinking.

You need:
-USB wall wart
-Perfboard
-Soldering Supplies
-USB male type A connector
-Load resistors (I think 10 ohm is standard, right? Correct me on this one if I'm wrong, anyone else who reads this.)
-Relay
-2 AA Batteries and Holder
-Led and Resistor

See the schematic below. Notice how the USB connector's power puts the LED in the off position. When there is no power, the spring in the relay completes LED's circuit.

Untitled Sketch_schem.png