My DIY Bluetooth Headphones

I made this thing that converts ordinary headphones into Bluetooth headphones. My laptop and phone both have Bluetooth so this will work great with them.

Roving Networks released a new Bluetooth module, the RN-52, that used the A2DP audio profile and outputted audio directly, without any configuration. I thought this was pretty cool. I’d much rather build my own Bluetooth headphones instead of buying them. So I decided to design a circuit to use the RN-52.

Like I said before, this module will output audio without any configuration steps, this means no programming or microcontroller required! This makes the circuit really simple. The circuit only has 3 sections: the RN-52, a power supply, and a audio amplifier.



The power comes from a 18650 rechargable lithium polymer battery. I picked the 18650 style because the charger is common (so I don’t have to build a craddle or dock or incorporate any recharge management circuitry), and the battery holder is also easily obtainable. I decided to design the PCB to be exactly as big as the battery holder, and add holes so I can either wear it like an lanyard or zip-tie it to my headphones.

The battery is regulated down to 3.3V with a LDO voltage regulator, which saves a lot of space and cost in comparison to a DC/DC step-up converter. There’s a Schottky diode (low forward voltage drop with good continuous forward current rating) to prevent damage if I insert the battery wrong, low voltage cutoff so I can’t over-discharge the battery. The battery itself also has protection internally for the stuff that might cause damage (warning, this is because I got a good high quality battery, not all batteries have internal protection!).

The 18650 battery is a beast and will last a few days, especially the high quality ones I have. I’ve actually done discharge tests with these and their capacity is truly what they claim them to be. Unlike cheap no-name brands who advertise 6000 mAH but only actually provide 1800 mAH. These ones claim to be 3400 mAH and actually deliver all of that.

The audio amplifier is centered around the TPA6112A2 operational amplifier. The circuitry forms a basic inverting amplifier with about 2X gain, and it can drive about 150 mW. The circuit mimics the recommended circuitry that is shown in the RN-52 datasheet and user manual…

…so this part of the project was easy to design. (protip: Don’t know what you are doing? Just copy the datasheet/user guide. This tip applies to all circuits!)

Add some status and power indicator LEDs, power switch, and a headphone jack, and the project is pretty much done. For those of you who are out of project ideas, see how easy it is to make an useful everyday product at home? Now I can walk around with my headphones without being tied to my computer by the cord. I know I can buy something like this for around $10, but that’s NOT FUN. I rather enjoy and take pride in making my own gadgets.

The schematic and PCB files are in EAGLE 6 format. Download them here: rn52headphones20130626.zip

Footnotes: It’s not exactly easy to solder this circuit because the opamp chip and the RN-52 have bottom pads that can only be soldered using reflow soldering techniques (hot air, oven, skillet, infrared, etc). I also designed it to support microphones, but that part of the circuit doesn’t seem to work, so I didn’t mention it as being a feature. (I probably made a mistake, meh, no big deal)

Another footnote: This is the 2nd prototype, the first prototype had volume control buttons and fancy stuff like that. But I couldn’t get those working under Windows because of a missing driver issue that I can’t resolve, Roving Networks technical support pretty much ignored me. So this 2nd prototype do not have those features.

Protip for you guys: use a blue, BLUE, emphasis on BLUE, LED for power indicators when you use a lithium battery and 3.3V LDO V-reg setup like I did. The blue LED will act as a low battery indicator, and become dimmer and dimmer as the battery is about to die. This is because blue coloured LEDs are made with a silicon junction that has a higher forward voltage than other colours. This higher forward voltage is typically around 2.8V, which is right around when a lithium battery is about to die, and a blue LED will become dim or stop glowing at all. If you used a green or red LED, their forward voltage is around 2V or lower, so even if your battery is about to die, the LEDs will still be brightly lit.


I may have given you a PCB. First check the revision number. The very first revision has the number 201306267. As of now, this is the only revision I’ve given out.

The parts you need to get:

Sch Ref Name Value Pkg Ratings Possible Part
  audio jack 3.5mm stereo     SJ-4351X-SMT from CUI
such as SJ-43514-SMT
BATT1 battery holder for 18650 batteries     BH-18650-PC or BH-18650-PC2 from MPD
RN-52 Bluetooth module       RN-52 from Roving Networks
SW switch       EG1390 from E-Switch
U1 amplifier   MSOP-10   TPA6112A2 from Texas Instruments
IC1 voltage regulator 3.3V SOT-23-5 500mA output, 5.5V input, 0.2V drop MIC5319-3.3YD5 from Micrel
IC2 voltage supervisor 2.7V SOT-23-3   TC54VN2702ECB713 from Microchip
D1 diode, schottky   SOD-123 20V reverse voltage MBR0520-TP from Micro Commercial Co, can be substituted
LED1 LED blue highly recommended 0603   generic
LED2 LED green or red 0603   generic
C1 capacitor, tantalum 10uF 1206 6V or more generic
C3, C4 capacitor, tantalum 47uF 1206 6V or more generic
C2 capacitor, ceramic 470pF 0603 6V or more generic
C5, C6 ignore        
C7, C8, C9, C10, C11 capacitor, ceramic 1uF 0603 6V or more generic
C12 capacitor, ceramic 100nF 0603 6V or more generic
C13, C14, C15, C16 capacitor, ceramic 100u 1206 6V or more generic
R1, R2 resistor, chip 1KΩ 0603 0.1W power, 5% tol generic
R3 resistor, chip 100KΩ 0603 0.1W power, 5% tol generic
R4 ignore        
R5, R6, R9, R10 resistor, chip 47KΩ 0603 0.1W power, 5% tol generic
R7, R8, R11, R12 resistor, chip 22KΩ 0603 0.1W power, 5% tol generic

23 thoughts on “My DIY Bluetooth Headphones

  1. Ricardo Chavarria

    Hi Frank,

    I was wondering if you could give me some info on what the chip/circuit for the headphones has in the middle? I can’t quite get it.

    I’m trying to do something similar to you and I’m having problems with radio/RF noise on the headphones coming from the module.

    Thanks!
    – Rick

    Reply
    1. Admin Post author

      Are you talking about the amplifier or the BT module? I’ve posted the entire BOM already and both of them are listed. RN-52 and TPA6112A2. All the circuitry is provided, and also the circuitry is based off RN-52’s application example schematic.

      Reply
      1. Ricardo Chavarria

        I was talking about the amplifier, I just didn’t see the label on the schematic, so I was wondering, but just did notice the TI part. Thanks!

        Reply
  2. Ricardo Chavarria

    Hi Frank,

    Sorry for bothering again, I was just wondering if you experienced any noise coming from the Bluetooth radio transmission into the headphones. I’m getting a lot of noise right now, but I haven’t added the amplifier and I’m wondering if this will increase or suppress the noise.

    Thanks!

    Reply
    1. Admin Post author

      The amplifier circuitry is more than just plain amplification. There is also appropriate filtering involved. The RN-52 probably should not be driving any sound output directly without an amplifier.

      It is impossible for RF noise to affect the audio quality of a digital audio stream, such as Bluetooth. This is because digital radios employ error checking techniques.

      I have never encountered noise in this project.

      Reply
      1. Ricardo Chavarria

        Thanks for the info. I assumed some of the extra circuits in the schematic were for filtering, but really didn’t know.

        RF noise is what I hear, not disturbance of the audio quality.

        Thanks!

        Reply
        1. Admin Post author

          You think you are hearing RF noise, but it is not. The noise is somewhere between the DAC and headphones, or the audio source and ADC of the input. The noise cannot manifest in the digital radio data.

          Reply
  3. arjun

    Great project. Eager to build it.
    I suppose sound quality depends on the headphone speakers. How good is yours? And what do you suggest to get some real crisp and full sound.

    Thanks.

    Reply
    1. Admin Post author

      I just use some cheap $10 headset, I am not an expert on sound quality, sorry. I suggest you try out headphones at the store before buying them.

      Reply
  4. Juhani

    Do you know how I could get the mic section working? Or do you know why it is not working? It would be a shame if I had wireless headphones but wire-mic.

    Reply
    1. Admin Post author

      I think there are two standards for 3.5mm jacks and I just designed for the wrong standard, maybe swapping the MIC and GND signals on the TRRS connector will solve the problem. Not 100% sure though.

      Reply
      1. Ghild

        Hi Frank,

        Did you test your microphone circuit ? I have problem with microphone input circuit, with refrence circuit I get static high pitch noise, but with your circuit, it’s clean but too clean, cannot pick any sound.

        Reply
  5. Gregor

    Hi, im from ARGENTINA, i liked your job , i want to do a similar project to recieve bluetooth signal to a big amplifier, to move some 2.1 speakers, what part of your PCB i need to look and take away the part of the power supply and amplifier that arre external?

    Reply
    1. Admin Post author

      You need to study the application example circuit diagrams, the ones provided by Microchip themselves, and figure this out.

      Reply
  6. arjun

    Hi
    Does your setup also allow to play audio from a 3.5mm jack, if bluetooth is not available in the source?
    Otherwise, what modifications would you advice.

    Thanks.

    Reply
  7. m88

    Hi! I just wanted to ask if you ever have any issues with hackers?
    My last blog (wordpress) was hacked and I ended up losing a few
    months of hard work due to no back up. Do you have any methods to
    stop hackers?

    Reply
    1. Admin Post author

      One of my domain’s email account got hijacked once and started to send spam to people, but my web host detected it and reset the password for that account, which stopped the problem.

      I don’t have any methods of my own. I am reliant on frequently updating to the latest patches and using good security practices (also weekly backups).

      Reply

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