Make’s latest Weekend Project combines two projects into one to create a piece of wearable fashion technology, the Solar Joule Bracelet! A joule (pronounced like “jewel”) is a unit of energy – in this project we’ll be sourcing that energy from the sun with the aid of PIN photodiodes wired in series, which along with a supercapacitor and Schottky diode will function as a solar battery (we built a similar project previously, the Solar USB Charger). This energy will then be stolen by the “joule thief” circuit, consisting of a choke (inductor coil), transistor, capacitor, and resistor all wired together. Oscillations through this circuit will eventually exceed the adjoined LED’s forward voltage rating, causing the LED to shine like a jewel! These oscillations occur in bursts, but once fully charged the oscillations will happen so fast the LED will glow continuously.
Together a solar battery (left) and a “joule thief” (right) power this Weekend Project!
The solid wire loops that connect the PIN photodiodes make perfect eyelets for sewing through, so we mounted ours on a cuff made from salvaged neoprene. Feel free to modify the design and install the circuit where and how you wish, for example on felt, onto a hat, or on your backpack – wherever you want a solar-powered LED!