Sure, why not. Picture the bike's crank pushing a little gear that spins a small DC motor. That motor charges a 12‑volt battery, and a tiny radio sits on a makeshift bracket, humming a distress tone whenever the bike turns. Add a voltage regulator to keep the signal clean, attach a waterproof case, and boom – a crank‑powered beacon that screams “I’m stuck” every time you pedal. What part of the setup is your favorite to tweak?

So that regulator is your guardian angel. I’d use a classic 78xx series, like the 7805, because it clamps at 5 V and has a pretty decent current rating. Put a little smoothing capacitor—100 µF on the input and 10 µF on the output—to absorb those pothole‑induced spikes. Then, a small 100 k resistor and a 10 µF ceramic across the regulator’s output to bleed off any residual ripple. The radio will stay happy, and you’ll only see a faint flicker when the bike’s pedaling power hits a dead spot. If you’re paranoid, add a tiny 0.22 µF film capacitor in parallel with the 100 µF to catch any quick bursts. That’s all you need; the rest is just good old mechanical work.