Well, I didn’t really write a blog post in a long time now… after dangerous prototypes and HACKADAY featured my blog I was kind of stoked with all the great responses! Thanks a lot for that! While that time I was also on a semester abroad in Malaysia doing some multi core embedded systems courses with focus on reliability. There I was digging a lot deeper into 8052 and ARM Core structures as well as more exotic ones like the XMOS cores. But now finally I am back – relocated to Munich for my master thesis – finding more time doing some nice electronics projects and writing about it.
Here it starts
I own a paar of Bose QC25 headphones for about a year now and it was a tough decision to make if you are a maximizer as I am. The main factors I considered were
- Sound quality
- Noise canceling
- Bluetooth support (aptX if possible)
- Play/Pause/Vol+-/Next/Prev Buttons
Long story short. The Sennheiser MM 550X’s sound quality was just ridiculous for the price, the audio technica M50X had really great audio quality not only for the small price but had a lack of all the other features and the AKG K550’s sounded reasonable but couldn’t hold up against all the features and quality of the Bose QC25.
So the QC25 (Quiet Comfort) feature good sound with and without batteries and do a perfect job with canceling any background noise. But… and thats the point of this blog… they do not have Bluetooth support. And I am about the change that.
Cheep BLE modules with all kinds of functionality are so cheep nowadays ready to get prototyped right form all these chines Web shops. I ordered 2 different modules to check them out without having the full plan on how everything should fit together. As I knew I needed some parts for sure, my first shopping cart looked like this:
I built the prototype by connecting one of the LiPo cells up to the charger and connected that then to the Bluetooth module which worked first go. The range was quite good and even stuffed inside my headphones with the metal shielding they work great. I had some issues with additional noise but I could have fixed these by decoupling. However I didn’t because the power consumption of this Bluetooth 2.0 module was with using about 56 mA just to high. So I had to switch to a BLE (Bluetooth Low Energy) module, to do what it says – use lower energy -.
In fact it did just that so that the battery should theoretically last far more then 15h which should be alright with a typical use. But I experienced some major problems with an ultra low range of just under 50cm without interruptions. that means with my phone in my pocket and the headphones on a simple move of my hand to my head will interrupt the playback and will ruin the experience… My plans for that is to try using different antennas maybe one which was designed for the ESP8266 Wifi module as it should also be trimmed for the 2,4GHz band or moving the module further away from the metal shielding inside the headphones. But… this is the point where I am right now.
Some inside views of the QC25
My plans with this project should not stop there. What I actually want to do is bringing this to the next level. I am planing on using a MSP430 ultra low power microcontroller to add some touch gesture recognition on the surface of the headphones to control the volume, play/pause, next/prev and possibly some more features. Also I want to add a microphone as the one built in the stock cable will not be used after the modification (as well as the buttons there). It sounds like fun to me and maybe you own a paar of those headphones too and join me on the mod.