HACKING BLUETOOTH FOR USB CHARGING
OR FOR YOUR OWN CHEAP 3.7v Li-Ion CHARGER
Found a cheap bluetooth headset but it's missing the charger? Wan't to salvage cell phone batteries or other Li-ion or Li-Poly cells but don't want to pay $20+ for a charger? Read on...
Lithium Ion batteries have been king of portable electronics since the early 2000 era. With good reason--they hold the most power per size/weight of any battery chemistry there is. But they are needly little buggers, sensitive to even 1v changes in charging or discharging. Personally, I've grown tired of spending $3 on protection boards only to break five of them building a new project.
And having to share a charger for my gazillion battery packs is annoying. But USB charging is ideal and an easy way of charging single cell li-ion.
What has both of these (circuit protection and charging circuitry)? and is cheap? Old Bluetooth headsets!
Here's the Motorala HS850
The important part here is the circuit circled in red. I've found this in multiple Bluetooth headsets and was at least standard for some time. It's marked "AZN" usually and through some miracle of Googling I found out it's a BQ24010
by Texas Instruments!
Very simple circuit that you can plug any 5v source into to charge li-ion batteries. Here's the schem info from the above PDF:
USB 5v in to pin 1....yep, it's that easy. Now you can use this cheap $5 headset as a 3.7v li-ion charger. :) or connect a USB plug to any Bluetooth you have with this chip.
and just in case your Bluetooth doesn't turn on and you want to fix it, look out for those protection chips circled in the pic above. Also standard packages used in multiple headsets. Usually the protection/monitor circuitry is a separate board on the battery itself, which makes sense since it is designed to break in case of a battery fault. You can trace the power output from the MOSFET and tie a new battery to there if yours is damaged.
Applications? Other than the obvious, it's great to throw this board in any portable enclosure with a cell phone battery for a great portable power setup. See the mic preamp project above for an example. This could also be useful for portable mixers, distribution amplifiers, headphone amplifiers, LED projects, and anything else you can think of!