This instructable goes over how to create a generator to power lights, charge a battery or capacitor, etc. with kinetic energy.
Stepper Motor (with 4 cables)
a load to charge or power
Step 1: Create a bridge rectifier using 8 diodes in a diamond formation
Step 2: Bridge Rectifier Breadboard
Step 3: Another view of the breadboard with everything plugged in
Here is a project that I created using this circuit:
Circuit Board (A board that lights up using the kinetic energy of the spinning wheel)