Origin of idea and summary of work
Years ago, my friend gave me "Beats" solo headphone which his friend "acquired". It didn't work so he asked me to hack with it. I found out that it was a demo unit and the batteries for active noise cancellation were not connected to the main cable leading to the analog board.
Some months ago I decided to give Dr Dre another shot. My plan was to put a rechargeable battery in the headphone with an added bonus of bluetooth connectivity.
You'll find a BOM in all of the zip's along with EagleCad files.
The output of the bluetooth is balanced but the input of the headphones is not.Word of caution, you can't connect the negative outputs directly to ground, they are being driven. I did, and it caused the module to shut itself off after a buzzing got too loud. After a whole lot of trial and error I finally decided to forego Dr Dre's noise canceling and gut the whole board out of there. That way I can connect directly to the cones and drive differential signal without rectifying anything. I also resized the lipo to fit onto the opposite side of the PCB. You'll notice that I took full advantage of the RN-52's buttons, as well as a toggling on/off button. It was meant to only turn on after 1 second of being held down but it seems like its more sensitive that that; oh well. The charging resistor is set for 100mA charging which takes the the 400mAh battery only 4 hours to charge. Charging is a simple micro USB cable, the Orange LED is on when charging, and Green LED when charging is complete. The whole board, while driving the cones at max volume, takes about 32mA which gives the whole thing a 10-12 hours battery life.
Some months ago I decided to give Dr Dre another shot. My plan was to put a rechargeable battery in the headphone with an added bonus of bluetooth connectivity.
You'll find a BOM in all of the zip's along with EagleCad files.
The output of the bluetooth is balanced but the input of the headphones is not.Word of caution, you can't connect the negative outputs directly to ground, they are being driven. I did, and it caused the module to shut itself off after a buzzing got too loud. After a whole lot of trial and error I finally decided to forego Dr Dre's noise canceling and gut the whole board out of there. That way I can connect directly to the cones and drive differential signal without rectifying anything. I also resized the lipo to fit onto the opposite side of the PCB. You'll notice that I took full advantage of the RN-52's buttons, as well as a toggling on/off button. It was meant to only turn on after 1 second of being held down but it seems like its more sensitive that that; oh well. The charging resistor is set for 100mA charging which takes the the 400mAh battery only 4 hours to charge. Charging is a simple micro USB cable, the Orange LED is on when charging, and Green LED when charging is complete. The whole board, while driving the cones at max volume, takes about 32mA which gives the whole thing a 10-12 hours battery life.
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Two boards, One Headphone
My first idea was to have a lipo charger/battery board on one ear and a bluetooth module on the other ear. Here are the parts broken up in two sections as I did them, before I had the common sense to put em on one board.
Charger
The charger board was based very much on the sparkfun Lipo Charger/Booster (PRT-11231). As you can see, the schematic is very much the same. When I wired it up tho, I could hear the switching regulator switching (or some harmonic of it.) So I desoldered that and dead-bugged an LDO on there for a clean 3V power rail.
Bluetooth |
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I decided on the cheapo bluetooth module "blk-md-spk-b-" which is strewn across the internet. You'll find all sorts of commands, guides, and instructions on how to interface with this thing. Mine turned on and everything, I could even see it on my phone, but it was always "unable to connect to bluetooth device". With everything I tried it was like that. I finally gave up and bought a non-random, non-chinese module form sparkfun (RN-52).
I got a lot of reference material from this guy's guide.
I got a lot of reference material from this guy's guide.
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