I love my Sennheiser HD-201 headphone. After years of use, it does not look like a new one but sure sounds just like a new one. Upgrading to a new headphone that supports bluetooth occasionally crossed my mind but the idea of dumping HD 201 was not convincing. A quick search pointed to two exceptionally helpful articles in Instructables (1,2) that made me confident to choose for a DIY route.
So here is my take on the steps to convert your headphone to a bluetooth headphone.
The goal of this article is to supplement the missing pieces in above mentioned articles. Please feel free to refer them.
I have tried my best to provide as much as details. Lets have fun!
Step 1: Take Your Toolkit
- Your headphone. Any make will work as long as it got at least ~ 4mm x 25mm x 20mm space in both sides. [FREE]
- Cellphone battery. I used Nokia BL-5C. The size was perfect within my headphone enclosure. [INR 250]
- Bluetooth stereo module. The one I bought was XS-3868 V3.0 [INR 375]
- Lithium Battery Charging Board [~INR 90]
- 3.5mm mini-Jack female [INR 10]
- Power switch -1 [INR 15]
- Tactile Push Button Switch 6x6x5mm, 5 nos. An example here.
- DC power jack & plug. An example here.
- 1mm wire
- A prototype PCB
- One stacking header with at least 12 pins
- Soldering flux (preferably residue-free)
- Solder wire
- Solder wick
- Electrical tape
- Hot glue + dispenser (optional, but helps to have one)
- Small screw driver set.
- Philips screwdriver (PH0, PH00)
- Soldering Iron
- Multimeter (Optional, but it always helps to have one)
- Scissors, tweezers, wire cutters
- Rotary tool with cutting and grinding bits (Optional, but it always helps to have one)
- mini-USB cable
- Cellphone charger
One more not so optional part: Patience (As much as you have).
Converting the total amount I spent to USD is less than $15.
Step 2: Get the Datasheet for XS-3868
This turned to be the first challenge. After referring to multiple sources I compiled all the needed info in to one.
Please note that this diagram contain pin info that is needed for this project. Pins without description means they are not needed or I do not know what they meant.
Step 3: (Optional) Solder the Pins to the Prototype Board to Test the Board
This instructable article suggest you to etch your own PCB. I tried this direction but it did not work out. Part of the reason is that the module that is based on is a bit outdated along with the EagleCAD and the PCB layout PDF. That design will not work for XS-3868. The pins are different. I did not have time to learn the tools to create a breakout board layout for XS-3868. I decided to hand solder the leads to the pins directly.
My first trial to solder wires was okay for some time. It helped me to try out the connections using a breadboard.
In my case, the play/pause button did not work. :(
But that solder did not last long. The final solution was to fix everything on top of a prototype board. Steps are described next.
Step 4: Soldering XS-3868
This is how I did it:
- Cut the prototype board so that it fits inside the grey outer shell.
- Use a double sided tape to fix the 3868 board to the prototype board.
- Mark the position of the 3868 board on top of the prototype board to make sure you have some extra space on the sides.
- Place it in such a way that you see the bottom of the board.
- Pullout around 12 pins from a stacking header.
- Even though there are 23 pins on 3868, we need only 12.
- Use your imagination, bend the two ends of these pins in such a way that it remotely looks like a very stretched version of english alphabet 'Z'.
- Solder one end of that bended pin to the prototype board. The goal is to spread out as much as you can. You should be able to solder the other end to one of the 3868 pins.
- Once you are in good shape, you can start connecting other components like switches to the board. Refer the diagram provided. Diagram courtesy to ClemRz who wrote this instructable.
Step 5: Connecting the Two Sides
We need to connect both sides of the headphone. I have decided to keep the battery and charging module on the left side and bluetooth module and other switches on the right side. I used an the stereo cable that came with my headphone. In effect you should have one cable for left channel and one cable for 4.7V power.
Use a double sided tape to fix it on the band.
Step 6: Fixing the Charging Module
- It is a good idea to check the board by connecting it with a 5V power source in one end and the battery on the other end.
- Once success go ahead and remove the micro USB connector. We do not need that. The connections are made directly to the board.
- There are two LEDs which are surface mounted on the charging module (TP4056). While charging, the RED one will turn on. While the battery is full, blue LED will turn on. Note that, these are really small.
- Make a note of its position and put some holes on the grey outer shell
- Use your glue gun to push glue through these holes. When correctly done, from outside these droplets will appear like the top of LEDs. And then the blue and red surface mounted LEDs are glowing, these droplets will act like lenses which adds a really cool visual effect.
- Your goal is to fix the battery and charging module within the grey outer shell. Do whatever is necessary to make it happen.
Step 7: Adding Control Switches
- Refer the connection diagram provided earlier.
- Design the alignment of the five buttons.
- Use the glue gun to fix the buttons on the grey outer shell
- Connect the power switch either on left side or on right side.
- I have connected the stereo female jack also. This is a back up option to make the headphone work without bluetooth module.
Once you have reached this far, I hope you are ready to rock.
Please share your experiences!
Here is a video of the output when the project was 99% complete.