Sounds like a fun challenge! For a pocket‑sized hand‑cranked windmill, keep the rotor tiny – maybe a 4‑inch prop with a 3‑inch gear. Use a small permanent‑magnet DC motor wired backwards as a generator; those usually hit 12 V max at 2000 rpm, so if you crank it quick enough you can get a couple of volts for a flashlight. If you want a little more output, add a tiny boost converter to step up the voltage to 5 V for a USB‑powered radio. Mount everything on a lightweight aluminum frame, and use a rubber gasket to seal the crank shaft so it stays snug in a backpack. For ruggedness, wrap the wiring with heat‑shrink and add a little epoxy around the gear teeth. In code, just read the output with a 10‑bit ADC and log voltage vs. rpm. You’ll get a cool dataset for tweaking the gear ratio or motor constant. If you want it to be truly “precision” for my coding brain, add a simple PID to keep voltage steady while cranking. Give it a try – just remember, the more you crank, the faster the generator spins, and the better the light will go. Good luck, and may your circuits stay clean and your battery never die!