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"Cozy" faux-leather universal USB / iPhone charger

All > Tech > Inventions > "Cozy" faux-leather universal USB / iPhone charger by natetrue

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Even in this connected world, we're not always near a source of USB power to keep our gadgets topped off. Recently during a power outage I realized the need for a way to keep my iPhone charged without mains power to keep me going - so I started researching solutions.

More recently, at the Consumer Electronics Show (where we were shooting a TON of video), my friend Andru's iPhone died every day because of how much usage it was getting.

So I looked around for simple and easy charging solutions. For a power source I decided on a lithium-ion battery pack, since they have such great energy densities. The pack I used was from an old Qualcomm phone, which I bought with charger from All Electronics, a surplus electronics shop. They don't have many Li-ion battery packs now, but sellers on eBay carry them very cheap. For example, you can get a HUGE Sony camera battery and charger for about 40 bucks, or smaller batteries for even cheaper (search for Sony camcorder battery and similar). It's better to buy pre-made batteries for products than buying bare cells, because they're often cheaper, and they include overload and overdischarge protection inside the batteries themselves.

Then comes the fun task of stepping the power down from the battery. It comes out of the pack between 8.4 volts and 6 volts, and since the iPhone can draw up to an amp from its supply, we need something heftier than a simple 7805 voltage regulator. I mean, a 7805 would work, but it would heat up like crazy and waste a bunch of your precious battery energy.

Enter the discovery of the Battery Elimination Circuit, something that is used a lot in the RC plane hobby. It's designed to efficiently step down any voltage of battery to 5 volts for control circuitry in model planes. The one I bought was based on the National Semiconductor LM2596S 5 volt switching voltage regulator.

5 volt BECs generally run about $25-$30 but their power efficiency is fantastic. You can find those on eBay too (search for 5v BEC). Try to go for the ones with only two sets of wires (battery in, 5v out). Speed controllers and such won't do us any good for this application.

So we've got the battery, and the voltage regulator. What's left? We need to trick that pesky iPhone into thinking it's plugged into its charger. Ends up there's some trickery you need to do with the USB data lines to get it to charge without doing a device enumeration first.

The trick is holding the D+ and D- lines at about 2.5 volts, weakly. I do that here by using two 100 kilohm resistors as a voltage divider, then connecting each of the data lines to the middle using a 1 kilohm resistor each.

The end result is a battery and power regulator combo that can recharge your iPhone (or other USB-chargable gadget) on the go without an AC power connection. I made it so that I could trade power sources on the go, just in case I had a solar battery down the line or something, to make it as versatile as possible.

On to the construction. This part's fairly simple:

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On the top we have the BEC, stripped of its heatshrink casing. I've removed the battery wires and in their place soldered a 2.3mm DC barrel connector. The mating connector is attached to the battery via a short length of flexible wire.

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On the back is mounted a little piece of perfboard, with wires going from the 5-volt out holes on the BEC to the USB conector. Here you can see the resistor network holding the data lines at 2.5v, plus another 1K resistor going to the little red LED that indicates power.

I salvaged the USB connector from an old broken USB 1.1 hub, which I replaced with some crazy new hubs.

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Now we've got a working product, but it's still bare electronics. They'd never let me board a plane with it looking all suspicious and improvised like that. It's got to look good, or at the very least innocuous.

Enter this faux-leather material that I bought at a local fabric store. It's expensive per yard but fortunately I didn't need much of it!

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The circuitry can be concealed within it easily.

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I just cut a couple of squares of the material and started sewing around, trying to wrap it fairly tightly. I would cut off the edges later.

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Here's the finished product, with a hole made for the power LED. Gaps in the sewing allow the USB and power ports to shine through:

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The power port kind of sticks out of the side like a sidecar sort of deal, because I really didn't have much space to put it elsewhere.

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And here's the USB port. I used pliers to flatten out the edges, as before they were flared outward. I didn't need any of that here, as it should all be soft and clothy.

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Here it is next to a bird for size comparison.

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The final solution is very pocketable and provides enough juice for about two full iPhone recharges. If I had used a Sony NP-F970 battery or similar, it could probably do more like 10 or 12 recharges. That's a lot of airtime!

Be sure to check out more iPhone stuff at cre.ations.net, and also check out iPhone Ringtone Maker, a great way to get unlimited free ringtones onto your iPhone (totally worth the money).

If you're looking into getting started with electronics stuff, also check out the kits I offer for sale.

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