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My first attempt at creating functional Bluetooth Headset was rather improvised and somewhat poorly planned. After it unexpectedly brought a lot of attention and with some very useful comments from other Instructables members I've decided to make an improved version of this device with some additional features.

It took me awhile to get this project finally rolling mostly due to parts availability, but it is finally here!

The old design did not have a proper charging ability, nor did it allow to use headphones in passive wired mode. It only allowed an initial installation and was too fragile for further improvement or even simple tinkering (we'll try to fix that).

My present goals are:

  • Reorganize electronic components to allow easy access for tweaking
  • Add proper (and fast) charging over mini-USB interface
  • Add support for passive mode (wired operation)
  • Add support for detachable microphone to make it a truly gaming headset
  • Add volume controls!!!

Step 1: Preparations: Gathering Tools and Materials

The list of tools and materials will be a little longer than for original build. There will be also an additional step to prepare a PCB to house the BLK-MD-SPK unit.

Parts:

  • Headphones (I'm using same old Sennheiser HD 201) ~free
  • Cellphone battery (In my case an old BL-5C,but anything that fits - works) ~free (around $3.00 new)
  • BLK-MD-SPK-B Bluetooth module ~as low as $7.50
  • Li battery charging module ~$2.50
  • 3.5mm mini-Jack x 2 (both male and female) ~$0.20-$0.30 each
  • Power switch ~$0.30
  • Small push-buttons x2 ~$0.20-$0.30

Tools:

  • Philips screwdriver (PH0, PH00)
  • Small flat head screwdriver
  • 40W Soldering Iron
  • Multimeter (just in case)
  • Scissors, tweezers, wire cutters
  • Rotary tool with cutting and grinding bits + a small drill bit for PCB holes
  • mini-USB cable
  • Cellphone charger

Misc. materials:

  • 1mm wire
  • Single-sided PCB
  • Soldering flux (preferably residue-free)
  • Solder wire
  • Solder wick
  • Electrical tape
  • Hot glue + dispenser (optional)
  • 2mm LEDs (red x 1, blue x 1) (optional)
  • Iron (III) Chloride or Sodium Persulfate
  • Acetone or acetone-based nail polish remover

Depending on which parts you already have and which distributor you get your parts from the total cost of this project may vary from as low as $10.00 to approximately $20.00 in worst case (tools not included).

PCB for this project will be made using toner-transfer technique, but any alternative(e.g. photoresist) will suffice.

Step 2: PCB

There are many ways to make a custom PCB at home. If you are an electronics enthusiast - you probably already have everything at hand. If not, you can easily purchase everything online including chemicals.

This was the first time I made a custom PCB, so I can tell from personal experience that it is very easy. The entire process takes at most 40 minutes, so if you mess something up - you can always start from square one.

I am using toner transfer method, so the list of tools and materials is composed accordingly. There are many tutorials here on instructables about making custom PCBs; I will only focus on critical moments of this process.

You can also check out my detailed tutorial on this topic:

Making custom PCB for DIY projects


TOOLS / EQUIPMENT:

  • Laser printer
  • Clothes iron
  • Soldering iron
  • Solder wick
  • Small plastic or glass container
  • Small drill or grinder

MATERIALS:

  • Single-sided PCB
  • Glossy paper (magazine page is your best option)
  • Acetone

Basically the entire process consists of the following steps:

  1. Print the PCB layout on glossy paper using BW Laser printer
  2. Attach the printout to the target space of the PCB
  3. Put a blank sheet of paper on top to prevent various residue from sticking to your iron
  4. Iron the board for a few minutes. Make sure you cover the entire surface of the print.
    Note: do not press to hard or set the temperature too high (toner melts at ~110C)! You can damage the PCB.
  5. Let it cool down for about 5 min and carefully put the board in a warm water bath
  6. Peel off the paper. In my case magazine paper fell off on its own, which was very helpful

Once you got this done you can start working on the etching process. Most of tutorials deal with Iron Chloride, because it is easy to acquire and cheap, yet in my case it was easier to acquire Sodium Persulfate for about half the price ($1.20 for 100g package). Another big plus of sodium persulfate is that it provides better edges and it is transparent (you can see exactly what's going on inside the etching bath).

Before you start - make sure all paths on PCB are connected. Any small flaws can be fixed with a thin black marker. Sharpie might be a bit too thick, so the best option for thin path correction is a 0.4mm marker pen, which you can get in any office supply store. Short-circuit spots can be corrected with an XActo knife, scalpel or a regular needle.

Dissolve 50g of sodium persulfate in 250ml of warm water(~40-45C). Submerse the PCB. Cook until done.

Normally the entire process takes about 20 minutes. Faster if you have a hotplate to maintain the temperature.

When etching is finished you can remove the toner with acetone and clean the PCB afterwards with a paper towel or a napkin.

Then cover the surface with soldering flux and start covering copper tracks with solder. Soldering wick is very helpful for tasks like these, because it allows to spread solder evenly, without leaving significant bumps or damaging thin copper lines with excessive heat.

You can solder a bluetooth module to PCB with either soldering iron or hot air rework station.

To make things easier I've attached EagleCAD files and PDF printout of this PCB.

Step 3: Installing Volume Control Buttons

Elecfreaks website has a nice reference on BLK-MD-SPK module itself and even has a simple diagram on how to connect buttons. That's what we are going to use in our design.

As you can see, there are several button configurations we can use. I've decided to make a simple 3 button configuration: VOL+, VOL- and MFB(multi-functional button used for play/pause/mute).

The construction itself is very simple: I've used a leftover piece of prototyping board and three 7mm pushbuttons.The only thing you need to pay attention to is that volume and playback controls are triggered from a 1.8V source(pin 24) and MFB button is connected to VBAT(pin 12).

After that we need to drill three holes to match our buttons. The control board is then installed and firmly glued to the earpiece cover. The end result is seen on the third image. Looks nice, but we are still too far from being done.

Step 4: Final Assembly

This time, in order to compensate for weight difference between left and right sides I've decided to put a battery with Li-Ion charger into the left earpiece, and the control board with bluetooth module into the right one. Pulling additional wires might be tiresome, but having your headphones constantly slide to one side during lengthy MMO session or a cool movie is much more frustrating :)

Due to the fact that this time we are also connecting 3 buttons, 2 minijack ports and a charge controller, there is gonna be a lot of things going on inside of your headset. You can see a semi-finished result on the picture above: it is going to get a lot worse! It is almost impossible to make a good pictures or video of this process, considering the size of the work area and the amount of connections we need to make, so I will include a detailed schematic with some annotations.

There will be 2 pairs of wires going from left to the right side: one for power and the other one for the left speaker. Optionally you can add another pair of wires for a microphone (if you are planning on using one).

A minijack for passive(wired) mode is connected directly to speaker wires, which means you have to disconnect it and turn the power switch off before charging (which is a normal thing for any battery-powered device).

Step 5: Evaluating and Testing

Connecting headphones to your phone or computer is quite easy: turn it on and start pairing, once you get the PIN pop-up, just enter "0000".

To demonstrate how everything works I've decided to make a short video, so enjoy!

<p>Hello,</p><p>first of all thanks a lot for this very usefull tutorial !</p><p>I would like to know if you had success with the microphone. I tried, but could not get it working... I used a microphone from an old phone soldered to MIC and Ground.</p><p>I found there (http://www.eevblog.com/forum/beginners/noiseinterference-on-bluetooth-audio-module-(blk-md-spk-b-)/ ) that &quot;the microphone is just not enabled for this version&quot;, which if true would be really bad to have a pin named MIC and not mention in the description that the mic is not enabled...</p><p>What are your experiences ?</p><p>Again, excellent tutorial :)</p><p>PE</p>
<p>I had the same problem. This is what I found. Hope this will help. :-)</p><p></p>
<p>Hello !</p><p>Thanks for your answer. Unfortunatly, I can't find any link or image in it... So what did you found ?</p><p>During my research for solving this problem I first found that : <a href="http://openrcforums.com/forum/viewtopic.php?t=3803" rel="nofollow">http://openrcforums.com/forum/viewtopic.php?t=3803<br></a></p><p>where I understood that the chip is not in a &quot;freehand mode&quot; and that we could set it to such a mode using the serial communication, but may be too complicated for me :(</p><p>So one may connect a computer to the serial port and send the order &quot;Unmute the mic&quot; from </p><p><a href="http://www.electrodragon.com/w/images/4/4b/BLK-MD-SPK-B_AT_Commands_OVC3860_List.pdf" rel="nofollow">http://www.electrodragon.com/w/images/4/4b/BLK-MD-...</a></p><p>which will turn it to a freehand instead of a headset in android point of view.</p><p>I'm not sure of what I say !</p><p>see :</p><br><p><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/4nbzP_m0iQ4" width="500"></iframe></p><p>for how to send message to the chip...</p><p></p>
<p>Sorry AroshaD I did not see your message...</p><p>I will try to build the circuit. Have you tried it yet ?</p><p>I am surprised because the module appear in android to be only a headset. Maybe after I connect the pins according to the diagram it will transform into a freehand.</p>
<p>For information about the microphone connection, see here.</p><p>https://www.instructables.com/id/XS3868-OVC3860-Bluetooth-Module-Microphone-Circuit</p>
<p>Hello.</p><p>you got some success with the microphone?</p>
<p></p>
<p>Hi! Your bluetooth headphones are epicly awesome!</p><p>Do you have any ideas how to detect current battery charge? Do headphones just turn off when battery reached 3.4v? Thanks</p>
<p>It shuts down when the battery reaches its low-point. But with larger speakers you'll notice lower volume and slight distortion about 30 minutes before battery dies.</p><p>It also has a built-in charging circuitry, but I am a bit sceptical to whether it will work as efficiently as a dedicated charge controller for batteries over 650mAh. Another reason for this decision is that I'm going to upgrade my power source to 2200mAh soon.</p>
<p>Thanks for answers! Two more little questions:</p><p>Did you tried to solder mic to bluetooth module? </p><p>Is it possible to charge battery and listen music in the same without wired (passive) mode?</p>
<p>MIC: I did solder wires and got a nice detachable microphone, but I can't find a non-PCB mountable minijack in any(!) store around. Going to Kiev tomorrow just to get one.</p><p>Here's the picture of what I'm going to use. I'll post the video of microphone test as soon as it is finished.</p><p>CHARGING: it is possible, but definitely not recommended. Just like with any rechargeable equipment you should never use it while charging. Li-Ion batteries have a strict charging cycle and charge controller makes decisions about the amount of voltage and current based on the battery status. While module is powered on it affects the state of the entire circuit and messes with controller feedback (e.g. controller only knows that there is only a battery hooked up).</p>
<p>Did you get mic working? Did you just connect directly? or used some extra components?</p>
<p></p>
<p>Did you get mic working? Did you just connect directly? or used some extra components?</p>
<p>Thanks for answers! Good luck with this and your future projects</p>
<p></p>
<p>Can i use extra Ampfilter ? Or how, because this module have his own ampfilter but not so strong for speakers :(</p>
<p>I'm sorry, I'm a little confused. I'm still ordering parts to build this headset and I am wondering if i need capacitors? I wasn't planning on using an amplifier... Do you think I will still get that little buzzing noise? I don't need them to be very loud, I'm still trying to choose a set of speakers to use.</p><p>So far I've got the battery, wires, switches, buttons, Bluetooth module and charging circuit. </p>
Also my headphones can fit certain sized 500mah batteries
Also my headphones can fit certain sized 500mah batteries
I found out I'm gonna have to shrink my materials. The li ion batteries I have barely fits and I've changed the pcb pattern and I might have to do it again. Is the pcb necessary?
Hi, my headphones have the jack insert on both sides (Monster DNA On Ear.)<br>Is there a way to keep those on and still make this project work on my DNAs?<br>I know I have to find a powerful small battery and my Uncle is giving me his broken Beats for testing.<br>Thanks in advance.
<p>Hi, I'm wondering if the volume control actually controls the device's volume?<br>Thanks!</p>
<p>Do you have a recommendation for a 4.0 module? </p>
<p>Hi, thanks for posting this instruction. Your steps best suits my need. I have a question on the schematics in pdf file. It looks little smaller to me. Is that a true size or need to enlarge it for the size match? PLease confirm. </p>
<p>That's the exact size for a standard Letter page. I've added 2 boards on a single print just in case one gets messed up, but if you are not sure about the size, or you only want to print a single board, you can print a PCB layout directly from Eagle CAD using attached schematic.</p>
<p>Thanks for your reply. I did took the print out and you are right. It matched good.</p>
<p>Hi,</p><p>I noticed that on the xs3868 chip there are two pins which I haven't been able to figure out the use for. One marked as vcc or charge and in one example USB, the other marked as led charge or led det. </p><p>These are different from the led status which is the bluetooth status led. </p><p>I'm wondering if this module has a lipo charger on there already. It would be a weird thing to combo but perhaps not really if they expect the device to be powered by a lipo all the time. </p><p>Is there anyone that knows for sure what these pins are for.</p><p>For reference I'm talking about pin 7,8 if you count from looking at the front top left, working your way down and around.</p><p>Thanks</p>
VCC[or CHG] pin is for built-in LiPo charger. It is slow, but works if you want to save a dollar and a bit of space. No one knows how powerful it is exactly, but there are speculations about 120-150mA. This chip was definitely designed for various types of small wireless headsets (e.g. earbuds). If you are using small low-power speakers and something like 450mAh battery, you can definitely use it. <br><br>My little monsters are powered by 1200mAh battery and I use them on a daily basis for 7+ hours at a time, so there was no way I could've gotten by with a built-in charge controller and smaller battery.<br><br>Then there are also 2 LED pins on the module: first one is a power indicator(RLED),and second one is Bluetooth connection(BLED). I've only used blue LED for connectivity status, since my LiPo charger already has power/charge status LED.<br><br>MIC and VMIC are microphone connectors. I guess there is a complete built-in circuitry to support the functionality, but (even though I wanted to do it since last year) I still had no chance to try it. Even have a modular mic with mini-jack connector laying around...
<p>Thanks for the quick reply and clearing up that for me ;).</p><p>If you don't mind how did you find that information? I did spend some time searching for data sheet and looking at other diagrams but didn't find any thing helpful in english at least.</p><p>One more question. I have hooked one of these up to an external amplifier, I am getting not quiet but not real loud buzzing (in addition to normal operation). I'd really like to fix it as it's loud enough to be annoying.</p><p>Seems unrelated to my audio source as when I turn the volume up the buzzing remains consistent. It's not real loud compared to max volume. </p><p>One other characteristic is that when music isn't playing there is no buzzing, I can only assume this is because the bluetooth module is disabling the output pin when there is no signal.</p><p>I have wondered if it's my power supply but I'm pretty sure that is ok as I have a 47uf and a 10uf cap both electrolytic on the input to the chip, and am using a 3.3v regulator (using LM1117T-3.3, as this is running on a 12v power supply). I did have the thought that electrolytic might not be right but to be honest I'm kinda a noob on this topic, a cap is a cap to me. </p>
<p>In order to get rid of the noise you need to add coupling capacitors for both speakers. My first module worked fine, but the one I got after had the same problem - really loud buzzing after BT connection. All I had to do is to add three 100uF ceramic capacitors in series and the noise was gone. Also improved sound quality and battery life.</p>
<p>Wow great! </p><p>Just so I have this clear (I didn't know you could put capacitors in series) you just have the caps hooked up to each other + to -.</p><p>Then put one end on the + output of the speakers and the - on the speaker ground. </p>
<p>I just looked up coupling capacitors. I didn't know they worked like that. Learn something new everyday. Thanks for your help mate I'll give it a go tomorrow morning but I think the largest ceramic caps I have on hand are .47uF. </p>
<p>You can try electrolytic caps instead: &quot;+&quot; goes to audio output, &quot;-&quot; to speaker.</p>
<p>Hi Again,</p><p>Tried some stuff this morning to no avail. </p><p>I tried 3 electrolytic caps in series 100uf. </p><p>Then tried 3 .47uf ceramic caps in series.</p><p>Then tried 8 electrolytic 10uf caps.</p><p>I have attached a scope read out of the noise (zero volume with music playing). My scope is kinda not the best... The min max of this is about 44mv and 10uS per divider. </p><p>Do I have a different problem perhaps? Or should I just get the correct capacitors?</p><p>Thanks mate</p>
<p>Show me how you connected caps to speakers or post a schematic. </p><p>In Step 3 image #1 there is a diagram for speaker connections. This schematic is taken from Elecfreaks documentation on this module and this is how I connected mine. Each capacitor is connected directly to speakers to block DC component of the audio signal. </p>
<p>Hey mate, I hooked them up like this. </p><p>The rest of the chip is hooked up the same as you have yours except that in this case I'm connecting to an amplifier so I can run some larger speakers. </p><p>Hang on a minute. I think I figured out the problem. </p><p>Do you need to put a cap on the gnd side in series also?</p>
<p>You only need one 100uF cap on each wire (AL, AR and AGND) for the amplifier.</p>
<p>Hello, sorry for the language because I am Brazilian.</p><p>I intend to do the same in my headphones as I found the idea brilliant.</p><p>I got doubt in capacitors used. It must be used for speakers of 32 Ohms right? Also like to know the voltage of these capacitors. Thank you.</p>
<p>Yup the more reading I did I realized my mistake. </p><p>Thanks for the patience!</p><p>I'll try it out tonight.</p><p>Thanks again!</p>
<p>Hi Again,</p><p>So I have rewired everything and hooked up the caps correctly. I still have the noise issue. I am wondering if the amplifier is at fault. I notice that the ground for the audio output is pretty much ignored on the amplifier. It's just using ground from the 12v supply. Which is the same ground as the xs3868, as the regulator I'm using is just a pass through ground. </p><p>So it seems I might need to have a separate circuit completely for this to work correctly. Or perhaps I'm just a boob and missed something else :). </p><p>Do you have any ideas?</p><p>Btw still using electrolytic caps.</p><p>Thanks for your help thus far <br></p>
<p>Yep. That's most likely the problem. I did this once on a broken module without the external amp(AGND pin got damaged). The noise is even louder that way. </p><p>Which amp are you using?</p>
<p>I have this one. </p><p><a href="http://www.parts-express.com/yuan-jing-tda7850-4-x-50w-audio-amplifier-board--320-6516" rel="nofollow">http://www.parts-express.com/yuan-jing-tda7850-4-x...</a></p><p>Hard to tell from the pictures, but I'm pretty sure it's a shared ground. </p><p>Mostly because it makes no difference if I have the ground connected or not. </p>
<p>Just verified continuity with a multi-meter. The audio ground is connected to the 12v supply. </p>
<p><a href="http://www.st.com/web/en/resource/technical/document/datasheet/CD00145702.pdf" rel="nofollow">http://www.st.com/web/en/resource/technical/docume...</a></p><p>Ok some more research. Looks like one of these guys. </p><p>So if I have this correct looks like SGND (pin 13) should be the ground. </p><p> Perhaps I can just cut the connections on circuit board and solder a wire from the audio ground to pin 13 on that chip? </p>
<p>It looks like it. </p><p>There's another thing - the amplifier has much higher impedance than speakers, so you can replace 100uF caps with something smaller: like 1uF, or 0.1uF (per datasheet).</p>
<p>Not sure if I'm reading the block diagram correctly for the tda7850, looks like internally the pwrgnd is connected to the s-gnd. I guess this means cutting the lines on the circuit board won't do anything? Or does the block diagram mean that it's not internally connected?</p><p>I can try putting smaller caps on the inputs but it seems like putting them on the audio out gnd (from the xs3868) is useless at this point?</p><p>Thanks mate let you know when I can try out smaller caps.</p>
<p>No, it is the external connection for basic reference circuit. You need to find an S-GND pin and disconnect it from PCB (de-solder and probably pull it out of the hole) and connect AGND to it. Alternatively you can try and run AGND signal through the third and fourth channel of the amplifier and make something akin to differential amplifier. But then you'll have to rewire outputs too.</p>
<p>Ok I'll de-solder it that seems like a better option then what I was originally thinking (cutting the traces and trying to make everything else work correctly). </p>
<p>I desoldered pin 13 and connected AGND to it now there is no audio at all. If I press the connection back together there is the same audio as before so haven't damaged anything permanently but the fix didn't work. </p>

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