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 |
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
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.
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!
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!
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.
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!
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.
can your bluetooth headphone transmit audio stream(as bluetooth transmitter)
The RN-52 has the ability to use a microphone but my circuit does not account for the microphone.
Is it dangerous for life? I mean bluetooth near brain?
thank you.
You are being paranoid. Try reading something like this article: http://www.robertsetiadi.net/wireless-radiation-mobile-phone-signal-vs-wifi-vs-bluetooth/
thank you , i will give it a try then ! 🙂
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.
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.
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.
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.
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.
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?
You need to study the application example circuit diagrams, the ones provided by Microchip themselves, and figure this out.
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.
I can unplug the headphone from the circuit and add a 3.5mm extension cable
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?
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).
please help, i am using RN 52 for one of my project ,it is disconnecting after connecting for 50 to 60 seconds ,i tried with Various Bluetooth compatiable devices,please can you tell how it actually worked,am really expecting answer from you
My number:9591941149
Email: samarthaggg@gmail.com
did you use microphone as a input or output?
I am working on same and wanted to use microphone as input, do you have any idea on it??
I bought a Headphone from super Market. It works very smoothly. Thats why I like it very much.
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.
Your ingenuity in creating a DIY Bluetooth headphone converter using the RN-52 module is truly commendable! The detailed breakdown of the circuit components, from the 18650 battery choice to the TPA6112A2 operational amplifier, showcases both practicality and technical prowess. The emphasis on easy replication through the datasheet/user guide is a valuable tip for aspiring makers. The blue LED low battery indicator adds a thoughtful touch to the design. Your commitment to the DIY spirit, even in the face of challenges with the first prototype, is inspiring. This project not only elevates the headphone experience but also embodies the joy of crafting personalized gadgets. Well done!