Our 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.
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! And when you do be sure to send us an email with your custom mod.
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