Power from a hand crank: the front end of an SOS wearable

Miners working in remote regions can't count on a charged battery when something goes wrong. The question behind this project was whether the motion of their own hands — the ordinary, repetitive motion of the work itself — could keep an emergency SOS wearable alive. My part, under my professor, was the electrical front end: the bridge that turns a piezoelectric element's messy output into something a device can actually use.

A piezo element under hand excitation doesn't give you power. It gives you brief, high-voltage, low-current bursts at whatever frequency the hand happens to move — and it stops the moment the hand does.

Fig. 01 — Open-circuit voltage of the piezo element under a single hand-crank excitation. Illustrative sketch; measured plots follow publication of the paper.

So the real design problem is harvesting: rectify the burst, boost it, and bank it — without spending more energy on the conversion than the hand supplied. That constraint shaped every choice in the A2D bridge and booster stage, and it's where I stopped thinking like a programmer with a soldering iron and started thinking like a circuit designer.

The full design is in our paper, currently under review. Title and status only until it's accepted — this entry stays at the level of what the problem taught me.