I recently got myself a nice headset. It had awesome audio quality and even noise cancelling which is perfect when studying. It was just one are it fell short - while using it I felt anchored by the pesky audio wire.
Now I really wanted a wireless headset, but those can be really expensive! This is the problem we are solving today. I'm showing you how to make your very own bluetooth adapter you can use on any headset you want!
There exist some finished adapter you can buy and I have tested a few of them. They often lack buttons for media playback, come with small batteries and short streaming time, and most importantly: a lot of them have really poor audio quality. I tested a few different pre made devices before finally taking the matter into my own hands!
The solution to this was to find cheap bluetooth earbuds with decent audio quality. And modify this to suit my music streaming needs.
That's what I'm showing you today. Let's get started!
Step 1: Parts and Tools
Step 2: The Road to Success
The plan is to rewire the audio cables so they no longer go to the earbuds. Instead they'll go to a female audio jack, so I can stream music to any headset and audio equipment I want!
An audio source sends alternating electrical signals to a speaker, through a wire. The electrical current drives small electro-magnets that will vibrate air. This is how the audible sound is generated. The only role of the wire in this scenario is to transmit the electrical signals. Nothing fancy is going on here. If we wanted we could cut the wire and connect it together again, longer or shorter, and the audio would still transmit just fine. This is the essence of what we're doing now. We're cutting the wire, but we're not directly reconnecting them to the speakers again. Instead we just use a male and female audio jack to reconnect the wires. This gives us exactly the same connection between audio source and speakers as before.
Step 3: Open the Old Earbuds
To get a look at what I was working with I cracked open the case on the old earbuds. Here I used pliers to apply pressure on the seam of the case until the glue failed and everything popped open. Now I cut the audio wires going to the earbuds. And trust me, cut these wires longer than you think you need. It's always nice to have some safety margin to work with.
After the wires are cut I peeled off the black insulation around the audio wires. While doing this I was careful to keep my thumb on the solder joints between the wires and the PCB. This was to keep the wires from being ripped off along with the plastic insulation.
Step 4: Wiring Diagram
I tested the PCB to find the positive and negative leads for the audio channels. This was done by streaming music to the bluetooth board and using a multimeter to probe the audio connections. I attached a couple of pictures to explain the wiring, so you wont have to test on your own.
Both negative leads go the ground pin on the female audio jack. In essence this means you only need to connect one of the negative audio wires to the jack.
Step 5: Audio Soldering
Thin audio wires comes with an insulation lacquer on the outside. I simply burned this off with a lighter, so they would accept the solder. To solder such thin wires I started by giving the wires and solder pads a small amount of solder paste, before tinning them with my soldering iron.
The solder connection is then made by holding the wires onto the solder pads and just lightly touching them with the soldering iron. The solder connection happens almost instantly!
Step 6: Button and Battery Soldering
While the original buttons worked great in the old case I needed another solution. I switched these out with tactile push buttons. The metal foil buttons can be carefully peeled off with a pair of tweezers. This will expose the button connections underneath and they just so happens to align perfectly with the buttons I got.
I snipped the leads on the push buttons much shorter on one side, and completely off on the other side. This makes them sit much more snugly onto the PCB. The solder connection is made in pretty much the same way as the small wires. First I tinned both connections before holding them together and lightly touching with the soldering iron.
I also wanted some extra playback time while rocking out to my tunes! So i switched out the battery to one that's more than twice as big. This gives a streaming time of 10 hours, instead of the standard four hours from the old battery.
Step 7: Testing Testing!
Now I've done a lot of modifications to the bluetooth board and I wanted to make sure everything still worked. I did this using an USB oscilloscope! I connected this to both audio channels. After pairing the bluetooth PCB with my computer I played a 20kHz sine way. This was transferred over bluetooth and out of the audio channels and visualized on my USB scope!
You can of course test this either with a multimeter or simply by connecting a headset to the PCB and playing some music. I just look for any excuse I have for pulling out my scope in the electronics projects I'm working on!
Step 8: Design Iteration
Making something as small as possible is always a challenge because of the tiny margins of error. This meant I had to go through several design iterations before I landed on the final design. I've attached the .stl files so you can 3D print the same case and everything will fit together. Guaranteed!
I used a pair of digital calipers along with Fusion 360, free 3D software for hobbyists! I've also attached the .f3d files so you can open this design in Fusion 360 and make your own design changes to suit your needs!
Step 9: 3D Printing
The parts are printed at the finest resolution of my printer, 0.1mm in PLA and with 0% infill as well as three perimeter lines. If you don't have your own 3D printer look into borrowing one at a makerspace, college, or library. Or you can use an online service like 3dhubs.com or shapeways.com.
While printing I flipped the lid 180 degrees and enabled support material. This was simply because my printer makes the top layer much much smoother than the bottom layer.
Step 10: Bringing It All Together!
Finally it's time to bring all of our hard work together in one tiny package! Most parts press fit inside the case. In the lid I started by laying down the PCB with the buttons sticking out of their holes. The microphone was pushed inside small hole that held it tightly in place. I gave the audio jack a small dab of hot glue before pushing it into the lid with the jack input sticking out.
Small magnets were glued on the inside of the bottom of the case. I also taped magnets in the corresponding locations on my headset. This makes it so easy to remove and fasten the bluetooth adapter on the headset!
When everything was in its rightful spot on the inside of the case, I pushed both halves together while adding a tiny seam of hot glue. If you're certain you wont have to open the case you can use super glue. I just like to have my electronics projects easily repairable if something were to happen!
Step 11: Finished!
That's it! Connect the bluetooth adapter to whatever audio jack you have, pair it to your phone or computer. Now you can finally rock out to your favorite tunes without feeling constrained by a pesky wire.
All in all I'm really satisfied with how this came out! The adapter works well with a decent range and long long playback time thanks to the battery upgrade. This DIY bluetooth adapter turned out to be a cheap solution for getting an awesome wireless headset!
Runner Up in the
Audio Contest 2017