This is just an example of what I am doing else.

This cheap dynamo flashlight was modified to include a USB port to charge electronic devices. The circuit is not hard to make, you need a 7085 regulator, a USB female plug, some wires, a soldering iron and hot glue. It is useful when you need electricity for a long trip.

This is not my first electronic device to be modified, I already modified a keyboard to control electric motors using a computer too. If you like it I will probably show other things I made.