As soon as we here at Revolt Lab heard that the Occupy Wall Street movement had come to our city of Boston, we immediately thought of how to put our maker skills in the hands of the revolution. Our first attempt has produced our Solar USB Box or SUBcomandante.
It consists of an array of solar panels mounted on a sturdy military surplus case, a 5 volt regulator, some capacitors, a switch, and a USB hub. The great thing about USB-charged devices and most cell phones is that they all take 5 volts! With this simple project, you can make yourself an emergency charger for phones, mp3 players, digital cameras, and other tools crucial to the revolution. Best of all, the simplicity of the design means beginners can understand how it works and learn to make their own!
I started with a case purchased from the army surplus store. This case was apparently used by Dutch forces to test air for poison gas and signal when it was safe to remove one’s gas mask. I found this instructional video of it in action:
The SUB circuit is very very simple. The 7805 reguator needs between 7 and 12 volts to put out a steady stream of 5 volts. Make sure that the voltages of your solar panels add up to between 7 and 12! When you have the proper amount of panels, wire them in series (positive to negative) until you have just one positive and one negative wire remaining. These wires will be your main power and ground wires.
On a piece of perfboard, place your regulator and capacitors according to the electrical diagram. Connect the capacitors to the regulator. Be sure to point the striped or negative side of the capacitors toward the middle pin of the regulator.
Use the diode (any 1n00x will do; I chose a 1n007) to connect the positive end of the solar array to a switch. Connect the other end of that switch to the left most terminal of the regulator. Make sure the stripe on the diode is closer to the regulator and farther from the solar array. This stripe indicates the ground or negative side of the diode. If you connect it backwards, no power will reach your device!
Connect the solar array ground wire with any remaining loose grounds on the board including capacitors and the middle pin of the regulator.
Finally, strip your usb hub or female usb cable and locate the red and black wires. Connect the red wire to the rightmost pin of the voltage regulator. Connect the black wire to ground.
You will notice that there are two regulators on my board. One is a 7808 8-volt regulator I had planned to use for recharging 4 AA batteries. Turned out all three regulators I had were duds! I did however get a chance to try out my new awesome desoldering pump graciously donated to the cause by the good folks over at Farnell (they run the element 14 site).
This tool would have saved me hours making the plantduino control board. It wisps away solder like magic, doesn’t burn or melt, and I can operate it with one hand! If you don’t have some kind of desoldering tool, get one. It is totally worth it.
When you have finished the wiring, wait for the sun to come out and check that everything is working!
I found that this set up will only charge my smart phone when it is off. As that is the state of my phone when I most need to charge it, I was happy that it could work in emergency situations. Try different panels and regulators (ALWAYS FIVE VOLTS!) to see what results you can get!
I used 5 minute epoxy to secure my solar panels, perfboard, and USB hub. Hot glue would work in a pinch.
To prevent my electronic devices form bouncing around, I attached a zipper pocket from an old pair of pants to the inside of the case.
Please leave any feedback you may have on how to improve the design or if you want to know more about building your own!
Get out there and MAKE REVOLUTION