Build It: DIY Juice Pouch

Today's messenger bag has become the urban pickup truck. Crammed with gadgets, gizmos, and paperwork; just open up the flap and toss in more electronic ephemera. Now it's time for your message bag to pay back for its wanton stuff gluttony and recharge your stashed goodies as you lug your battery-powered electronics around town.

Get your messenger bag up to speed and equip it with a photovoltaic-powered charging circuit. Not just any photovoltaic panel will do, however. It needs to be lightweight, flexible, weatherproof, and powerful. Likewise, the connector for this solar-powered recharging system needs to simple, foolproof, and compatible with the largest number of your electronic gadgets. The thin film plastic solar modules from PowerFilm (formerly Iowa Thin Film Technologies) coupled with a USB female connector are the perfect combination for transforming your overloaded dolt messenger bag into a messenger bag loaded with volts.

2 hoursCost: $45.03Very Easy

Parts List

• A Messenger Bag (FREE)
• Iowa Thin Film Technologies PowerFilm WeatherPro Series P7.2-75 (Jameco #228161; $39.89)
• USB 6' Cable w/Female Connector (Jameco #222068; $1.65)
• 78M05 Voltage Regulator (Jameco #192233; .19)
• 0.47mF 50V Electrolytic Capacitor (Jameco #330464; .04; substitutes are OK)
• 0.1mF 50V Tantalum Capacitor (Jameco #545570; .31)
• Salvaged Plastic Project Box (FREE)
• Clear Vinyl Sheet (craft store; .50)
• Large Eyelet Kit (craft store; $2.45)
• Alligator Clips
• Wire

NOTE: There are four distinct subassemblies which constitute our Juice Pouch: (1) modified messenger bag, (2) photovoltaic panel, (3) voltage regulator, and (4) USB connector.

Depending upon the style of your messenger bag, you may or may not have to perform any or all of these modifications. Generally, the outside flap of the messenger bag should be equipped with a clear pocket for holding the photovoltaic panel. You can make your own clear pocket from vinyl sheet. Likewise, you will need several grommets or eyelets for routing your cables through the messenger bag. Add as many eyelets as necessary for connecting your charging "dock" with the voltage regulator and the photovoltaic panel.

Preparing the photovoltaic panel has been simplified by the manufacturer-attached solder tabs. These tabs are pre-wired as positive (+) and negative (-) terminals. Either solder directly to these tabs or use removable clips for greater flexibility in moving the panel in and out of the bag.

Determine the positive and negative terminals on the photovoltaic panel with a multimeter. Mark the positive terminal for easy identification.

Mount the 78M05 voltage regulator inside your salvaged plastic project box.

The two capacitors must be soldered to the 78M05 voltage regulator. The positive lead of the 0.47mF electrolytic capacitor is soldered directly to the input lead of the 78M05 voltage regulator. Conversely, the positive lead of the 0.1mF Tantalum capacitor is soldered to the voltage regulator's output lead. Finally, the negative leads of both capacitors are soldered to the ground (GND) lead of the 78M05 voltage regulator.

Snip off and discard the male connector from the USB cable. Open this newly exposed cable end and separate the four wires: red, black, green, and white. The green and white wires are USB data lines and they are not used. The red wire is connected to the output lead of the 78M05 voltage regulator. The black wire is connected to the voltage regulator's ground lead.

Connect the photovoltaic panel's positive terminal to the input lead of the 78M05 voltage regulator and the panel's negative terminal to the voltage regulator's ground lead.

Place the photovoltaic panel in direct sunlight and test the voltage readings with a multimeter at these four points: photovoltaic panel terminals (you did this test in Step 2), voltage regulator input, voltage regulator output, and USB pin 1 + 4. The readings at the first two points should both be approximately 7 - 8 volts. The readings at the last two points should be exactly 5.15 Volts. If you obtain valid voltage readings, try connecting one of your USB-chargeable devices to the Juice Pouch's output USB female connector. During testing we found that iPod nano (first generation) and Sony PSP charged reliably with this setup. Unfortunately, we were not able to charge a Motorola RAZR V3 phone or an iPod shuffle (first generation).

If everything checks out, assemble the photovoltaic panel, voltage regulator, and wiring inside your messenger bag, hook up a suitable device and charge out there.