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Here Is What's Required For This Build.

Tools

• Soldering Iron
• Glue Gun
• Wire Stripper and Cutter
• Electrical Tape

Materials
• an old CPU fan
• toroidal inductor
• 2N2222 or 2N3904 or BC547 transistor
• 5v step-up module, (boought on eBay)
• germanioum diodes (5 pieces)
• a small perfboard
• an old phone battery or a 18650 cell
• and a small switch
• bike support element

The fan is going to generate an AC voltage which gets converted to DC with a Joule Thief circuit and charges a battery.

Image Source

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Now Let's Start Building

The complete instructions can be found at the Insructables page