Quick update on an early prototype of the "Portable Energy Scavenging Kit", after a intense hackathon this weekend with Ben Garmari:
This first version of the kit is able to charge phones that require 5 Volts, 500 mA, and it can also power a small LED light (suitable for lighting a small space, or usable as a flashlight). It uses a rechargeable battery (the amount of energy the battery can store is 6600 mAh -- a typical smart phone battery capacity is about 1500 mAh) which can be charged either by house current (via an adapter), or via a small solar panel (3.4 Watts, 6 Volts). We haven't yet tested how long it takes to charge fully a battery of this size; but the panel typically outputs 500 mA in bright sunlight, so acquiring 1500 mAh (one smart phone battery's worth) should take around 3-4 hours.
More photos here: https://www.flickr.com/photos/80184146@N06/sets/72157632268859995/
Ingredients: * 3.4 Watt 6 Volt Solar Panel ($30, voltaicsystems.com) * Solar / DC / LiPo charger ($25, adafruit.com) * MintyBoost v3 kit ($20, adafruit.com) * A 6600 mAh LiPo battery ($40, adafruit.com) * Buck Puck DC Power ($20, superbrighleds.com) * A 1 Watt LED ($3, adafruit.com) * Piece of PVC junction ($.49 at hardware store) * USB Mini-B, USB Micro cables ($1 ea on Ebay) * Altoids-like tin (< $2)
Next steps: * Design a custom PCB. The next version will simply combine the MintyBoost, Solar Lipo, and Buck Puck charger circuitry in order to reduce costs. And hopefully subsequent version will use an Arduino-like chip to allow for charging other battery chemistries and for optional output of, e.g., the 700 mA that a Raspberry Pi prefers. * Design a case for the battery and electronics