Last year I made several popular instructables on creating cheap and easy to build USB Chargers. Many people have emailed me about these and offered up many constructive ideas and comments, which lead me to reflect on ways to improve my design. So after a full year of minty smelling solar USB chargers, I submit to you my Heavy Duty Solar USB Charger (which still fits in a tin).
In my original designs I used a small 4V solar cell to charge up 2 rechargeable AAs, which in turn powered a boosting circuit which charged up your gadget. The construction difficulty was low enough that even beginners could accomplish this, and the cost was low enough that even if you did screw up, you didn't break the bank. The only weak part of the project was the 4V solar cell. While it was powerful enough to charge up the internal AA batteries, and small enough to fit into the tin, it was in no way powerful enough to directly charge a USB gadget on a sunny day. I'd also gotten quite a few emails from bikers and hikers who wanted a solar cell that they could mount on a backpack while traveling, something the 4V just wouldn't do.
To combat this, I've switched up the design and gone with a much more powerful solar cell. To combat the fact that no one likes to carry around a massive solar cell (unless you're a hiker) I've gone with a jack and plug system. Still easy to use, easy to make, and it won't break your monthly tinkering budget.
The USB Boosting Circuit in this kit works with most USB gadgets. I've tried it out on old and new iPods, iPhones, Kindles, GPS Units, and Android Phones. While I can in no way test every USB gadget on the planet, from what I have tested the circuit seems to play nice with most gadgets out there.
More or less, this is the last Solar USB Charger you're ever going to need to make.
Cool Factor: High
Ability to get you a date: Low, unless your date is an electrical engineer in which case "high"