Introduction: DIY Bluetooth Audio Adapter - BluFi

About: I am an 18 years old hobbyist who finds a great drive in tinkering with electronic circuits. The reason I love electronics is that it empowers me to solve real-life issues with ease. I also enjoy making gadget…

There isn't a single audiophile or a gamer who doesn't feel the necessity of wireless headphones, speakers etc. or simply, of wireless audio transmission. I also dislike the hassle my wired headphones present while trying to watch from a distance and this led to the inception of BluFi.

This adapter, BluFi, converts any audio accessory into a wireless audio accessory. Since it has an in-built TRS female jack, therefore any audio accessory having a male TRS/TRRS jack can be easily plugged into it for Bluetooth audio reception. For instance, your wired headphones can be made wireless by simply plugging its audio jack into the adapter and then pairing the adapter with the phone.

BluFi is based on XS3868 module which is powered by a 3.7V rechargeable lithium-ion battery, therefore you won' t have to worry about exchanging the batteries. It also contains a Female USB 5V DC output socket for powering any USB speakers directly through it. The TP4056 charging module has also been integrated into it for hassle-free and quick charging through our familiar Android smartphone chargers(USB-C port).

The reason why I preferred an adapter to integrating it into audio accessories is that this way, our expensive audio accessories won't be tampered with. I also needed something to convert my car's speakers to Bluetooth without any modification to the car(because I wasn't allowed to do so) and that's how BluFi came into being. Additionally, BluFi, being an adapter, is portable and much more compact.

Step 1: Gather Around Some Stuff

The requirements for this project are very basic. The only thing you require additionally is the XS3868 module which can be purchased online.

BluFi is the combination of two circuits, namely, XS3868 circuit and MC34063A DC-DC booster circuit. Therefore, I'll be splitting the requirements into two sections for better understanding.

Concernig the microphone, if you want to provide microphone input through your earphone or TRRS jack, ignore the GND connection of microphone in schematic and connect the MIC pin of TRRS jack to the resistor and capacitor as shown in the schematic without any changes."

XS3868 Circuit Requirements:

  • XS3868 PCB.
It can't be bought. We'll have to make it ourselves. The procedure is shown from the next step.
  • XS3868 module - 1 pc.
I had bought it from Aliexpress. This is the link.
  • TRS Female Audio Jack - 1 pc.
  • Microphone - 1 pc. (Optional)
  • Lithium Ion Battery (3.7V) - 1 pc.
  • TP4056 Charging Module - 1 pc.
  • Tactile(Push) Switch - 5 pcs. (Optional)
  • Capacitors:
    • 47uF -1 pc.
    • 220uF - 1pc.
    • 0.1uF - 1pc.
    • 2.2uF - 1 pc.(Optional, for mic)
  • Resistors:
    • 2.2k - 1 pc. (Optional, for mic)
    • 10k - 1 pc.
    • 470R - 1pc.
  • LED - 1 pc.(Optional)
  • Female USB Socket
  • Female Headers.
  • Slide Switch - 1 pc. (Opitional)
The switch is missing in the picture because initially I had planned to use terminal blocks for powering up the circuit.

3.7V Booster Circuit Requirements:

  • MC34063A Booster PCB.
The procedure to make it is covered afterwards.
  • MC34063A - 1 pc.
You can buy it from Aliexpress from this link.
  • 8 Pin IC Base - 1 pc. (Optional)
  • 100uH inductor - 1 pc.
  • 1N5819 Schottky Diode - 1 pc.
  • Capacitors:
    • 100uF - 1pc.
    • 10uF - 1 pc.
    • 1nF - 1 pc.
  • Resistors:
    • 180R - 1 pc.
    • 22R - 1 pc.
    • 12k - 1 pc.
    • 3.9k - 1 pc.

That's all for the requirements. Let's move ahead and start making the PCBs.

I'm posting the schematics for reference and modification purposes.

If you're unable to gather the materials required for the 3.7V booster, then alternatively you may buy this or this instead of making it. Even I had faced a lot of difficulty in finding the 100uH inductor.

Step 2: The XS3868 PCB


I'll be making this PCB using the toner transfer method. To make this PCB, you're going to need the following:

  • Copper Clad Board - Approx. 6.5cm * 3.5cm
  • PCB Drill
Don't have one? Here's how you can make one.
  • Zero Grade Sandpaper
  • Clothes Iron
  • Glossy Paper (The kind which is smooth in texture)
  • Etchant Solution
I'll be using Ferric Chloride.
  • Any PCB Cutting Tool
I'll be using my thermocol knife and scissors in combination.
  • A Permanent Marker
In case the toner isn't perfectly transferred, this marker will be used to cover the incomplete traces.

Making The PCB:

Since making the PCB alone is an entire instructable, I wouldn't go into detail on that topic. Here is an instructable which you can refer to for making PCBs.

On a side note, I'd like to add that sanding the copper clad board with a zero grade sandpaper before ironing gives better results.

I've attached the layout PDF file as well as the original EagleCAD board file so that you're also able to modify it yourself.

After the PCB has been successfully made. You can follow the next steps:

  1. Drill the holes.
  2. Add flux to the entire trace network and then cover the traces with solder by gently pressing the soldering iron's tip at a low angle on the traces. This step is important because the traces of this PCB are thin and adding solder strengthens them. It also eases soldering.
  3. Add the jumpers. Refer to the "Jumpers" picture above.
I have used enamel coated copper wires(salvaged from non-working earphones) for this purpose because they can be made to overlap each other without shorting and they occupy very small space as well. They look kinda neat too!

This concludes the XS3868 PCB making. By the way, the schematic on which this PCB is based is attached in the previous step. You may refer to it for checking your PCB traces effectively.

Step 3: The 3.7V Booster PCB

Making this PCB requires the same stuff and same procedure, therefore there's no need for repeating all that.

However, since the traces in this PCB aren't thin, you can ignore the soldering the traces part.

The layout PDF and Proteus project files have been attached.

Please keep in mind that the Proteus Project files and PCB layout have been modified. But they still follow the same schematic. Therefore the component placement might not be identical.

Step 4: Finishing the XS3868 PCB

The XS386 PCB, as it is now, is just like a soulless body. Let's bring it to life by soldering in all the circuit components!

There is no definite order of making this circuit, however, for illustration purposes, I'll be demonstrating things step-wise.

Soldering The XS3868 Module:

Pick up the XS3868 module and place it on the PCB solder pads such that no pads are interconnected. Holding the module in place, carefully solder the corner pads.

If you want to be extra careful about your module placement, you may use a small amount of glue to stick the module with the PCB.

Once that is done, proceed carefully with the rest of the pads. You have to be careful because the pads are easily dislodged from the module if they are heated for a long time. Therefore try to do it all in one go!

Soldering The Rest of The Components:

  1. Pick up the USB Female socket and the TRS Female Audio jack. Place them on the PCB and solder them.
  2. Grab the TP4056 charging module and stick it on the top layer using superglue. If the module's holes and the PCB's holes aren't merging with each other, don't worry, I've left sufficient place for drilling. Therefore simply drill new holes according to the new placement. Once that is done, connect the module power pads with the PCB from the top to the bottom using leftover, trimmed component legs.
  3. After that, solder the 470R resistor on the copper side as shown in the picture above. I have used a 4.7k resistor instead because I didn't want the LED to glow too brightly.
  4. Now it's time for the indicator LED. Double check the polarity and solder it as shown in the picture.
  5. Pick up the 10k resistor and place and solder it as done in the picture.
  6. Do the same with the capacitors.
  7. Now let's add the female headers.
  8. Now all that's left is the switch and the battery.The switch will be used for switching ON/OFF the circuit. The pictures for this step too have been posted as a reference.
The headers in 7th Point above can be used for adding the button controls such as Play, Pause, Next, Back, Volume Up and Volume Down. They may also be used for adding an external mic! Same goes for UART communication. The pin configuration of the sockets will be described in one of the next steps.

By the way, if you're wondering about the switch step. I didn't initially think of adding the switch because one of my batteries has an external switch attached to it.

That brings the end to the XS3868 PCB job.

Step 5: Finishing the 3.7V Booster Circuit

This circuit will be used to boost the 3.7V input from the Lithium-ion batteries to 5V DC which may be later on used for powering up our USB speakers.

To complete this PCB, refer to the PCB component placement guide posted above and solder everything in place correctly. I'd like to remind again that due to layout modifications, my PCB's pictures might differ from the layout. Therefore give the component placement guide higher priority.

I have posted my PCBs pictures as well.

There's a lack of pictures and procedure directions in the Booster PCB because I forgot to take the pictures. I'll be posting a separate instructable on it in much more detail. Till then, please manage with the schematic and PCB project files.

Step 6: Testing the XS3868 Circuit

Now's the time when we get to taste the fruits of our efforts for the first time because this is the testing phase.

Then test the circuit, follow these steps:

  1. Connect any audio accessory to the circuit by plugging in its jack into the TRS Female jack.
  2. Power on the circuit by sliding the switch. You should hear a jingle from your audio accessories. If you don't then, re-check the previous steps.
  3. Pair up your phone with the XS3868 module and start playing some music. If you're successfully getting audio through your audio accessories, then you may proceed to the next step.
The XS3868 module, by default, shows up as POR1007BT when searched-for by any device.

Step 7: Integrating the Booster Circuit With the XS3868 Circuit

We have finished most of the work now, all that's left now to finish BluFi, is to integrate the power booster circuit with the XS3868 circuit.

This can be done by connecting the Power Out pads of Booster PCB to the USB Female socket. There are holes for this purpose below the USB socket. After that, connect we need to give something to the Booster to boost, that is, 3.7V in. This can be done by connecting the input terminals to the switched terminals of the Lithium-ion battery.

You may refer to the above picture for more aid.

After that's done, try to hook up any USB powered gadget to it and it should power up. I have powered up my Arduino UNO(programmed with blink sketch) with it.

Step 8: The Headers

You have finished making BluFi but you still don't know it's capabilities and upgrades. Therefore this step will be completely dedicated to female headers on the XS3868 PCB which may be used for quite a lot of things!

The Button Controls Header:

BluFi supports a maximum of 5 button controls, namely Volume Up, Volume Down, Next Track, Previous Track, Pause/Play. To be able to use these controls, you'll have to connect Tactile Switches from any one socket of the Button Controls header to the COM socket present at the end of the same header. This may be done for all the controls.

I have posted a picture of my button controls extension above. You may refer to them making yourself one. The yellow wire(the shorter one) has been intentionally made short so that it looks different from the others because it is the COM pin which has to be inserted at the end of the female header.

The MIC Header:

If you're intending to use a mic as well with BluFi, you can do so. To do this simply make a small circuit based on the MIC schematic posted above. After that, connect the MIC circuit wires to the headers accordingly.

The UART Header:

The XS3868 module is, in fact, capable of communicating through the UART protocol. This enables the user to configure the chip according to his needs. The basic uses of this header include changing the name, pin, tones and other settings of the adapter. I have covered all these operations in another instructable here. You may also use this header for integrating the adapter with I/O devices or with Arduino by making them work in tandem through the commands provided in the OVC3860 datasheet. Refer to Step:5 and wiring of the above-linked instructable to see how AT commands are sent. I have attached the PDF containing details about the AT commands below. The Rx and Tx sockets have been marked in the above pictures.

Step 9: Congratulations!

That's it! You have now finished making BluFi and may use it according to your needs.

Since I'm not very good at packing things up, I'll leave the enclosing part of BluFi up to you. Please post pictures of how you enclosed it through "I Made It". The one which I'll find good will be posted up in this step with the uploader's name mentioned as well.

Anyways, now you have your own Bluetooth adapter and are now able to listen to audio wirelessly. And the best part is, you made it yourself!

Wireless Headphones?

If you want to use it with your headphones, simply tie up your headphone's cables to shorten them and connect them to the adapter. Place the adapter on the headphones top using Velcro or anything, and voila! you headphones are now wireless.

That's it for this instructable.

I'd appreciate it if you support me on Patreon.


Utkarsh Verma

Thanks to Ashish Choudhary for lending his camera.

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