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Ridiculously bright keychain rechargeable flashlight / flash drive

All > Tech > Inventions > Ridiculously bright keychain rechargeable flashlight / flash drive by natetrue

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Being a lover of putting super-bright lights in things, I wanted to make a compact keychain flashlight that was rechargeable. Obviously USB is the standard for powering small devices now so a USB connector was an easy choice.

I happened to have a spare tiny USB flash drive around, so how better to get USB power than to also be a flash drive? That way it has a double use on the keychain.

I decided to go with the MAX1555 lithium-ion charging IC (same one from the binary watch project), and an 80 mAh lithium-polymer battery from All-battery. The battery has about the same size as the rectangular USB connector and so works well for this project. It also includes a protection PCB pre-connected to it (if you choose that option when you buy it) so that if I make any crazy mistakes it won't explode the battery. Convenient, eh?

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Here's the flash drive extracted from its plastic enclosure. It's easy to remove and the ceramic inner module is small enough to fit into a metal USB connector casing that I salvaged from elsewhere. You can see I have soldered the MAX1555 chip directly to the power pads on the flash drive. If you're doing this yourself, remember that in such small things as the flash drive and MAX1555 chip, heating for too long with a soldering iron can destroy them. Best to solder it as quick as you can, and make sure your soldering iron has a nice sharp tip to get good precision.

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Here's the battery attached to the drive and charger chip.

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The light module is made of 8 ultra-high-brightness 17,000mcd white 3mm LEDs (also from the watch project) wired all in parallel. Their forward voltage is about 3.58 volts. That's perfect for the Li-poly battery, which ranges between 4.2 and 3.6 volts over its charge life.

I used a 10 ohm resistor in series with the light module to limit the current to about 80 mA, which is the maximum peak discharge current rated for the battery. Since it's activated by a momentary pushbutton we don't have to worry about the rated 16mA continuous discharge current limit.

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Here are all the electronics assembled together in roughly the shape they will be in the final product. Note strategically placed electrical and double-sided tape to insulate the parts from each other and to hold things in place.

Also note that the flash drive fits almost completely in the metal USB connector and so doesn't take much extra room. The charger chip is also in the metal part and is protected with electrical tape as well.

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I put on a structural layer of epoxy putty to make the whole thing rigid, so it won't change shape during the more-pressure-required full enclosure phase. Time was allowed for the epoxy to stiffen up.

I decided to go with a full-epoxy casing because it's easy to make and sculpt, and because it will rigidly hold all the parts exactly in place, firming up any possible loose connections and filling gaps to keep wires from touching what they shouldn't.

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Adding more epoxy putty covers all the electronics and gives it an organic, amorphous yet functional and compact shape. A wet finger is used to smooth the epoxy. Note in the above picture that the device is upside down, so the button is on the bottom and not shown.

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A view of the epoxy around the button. Later I built up that area more to avoid accidental presses while in a pocket.

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I took the rectangular part of the keychain side from an old Sandisk Crossfire drive that holds the USB connector securely to a keychain but allows it to be removed too. A simple strip of brass is soldered to it to attach a keyring (in the photo it's held up by a stack of magnets).

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And here's the final product after painting. I put a simple design on the front to distract you from its blobby form a little.

The battery should give a little over an hour of light and the Li-poly chemistry has a very low self-discharge rate so it should never have to be intentionally recharged if used regularly as a flash drive (it takes about an hour to recharge from USB if fully discharged first).

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