I had an old pair of Sennheiser headphones, and i thought i could something fun with them. At first i wanted to just make them in to a set of USB rechargeable wireless bluetooth headphones, but there was absoutely no room in them for the electronics.
So i decided to build it into an old set of hearing protection i had i my scrap-bucket, and hopefully make them a bit noise cancelling. It turned out great, and they kept a lot of their sound proofing abillity.
here is a parts list for the build:
• Donor headphones
• Hearing protection
• Li-Ion battery
• Bluetooth module
• USB Li-Ion charge controller
• 3-5v -> 5v step-up (OPTIONAL)
• SPDT switch
• Diode (pretty much any will do, NOT an LED)
This is not a particularly difficult build, but some soldering experience is definitely recomended as well as a basic understanding of electronics(it is really simple stuff, so no worries if you don't have much experience :P ).
here is a list of tools needed:
• Soldering iron and soldering tin
• Utility knife/wire stripping tool
• Hot-glue gun
This was actually really cheap to make, it cost around 15$ because i had the headphones already.
Ok then, lets go! :D
Step 1: Preparation
First thing i want to do, is disassemble the hearing protection and the headphones, so you know what you are working with. I was really lucky that the speakers from the headphones almost fit perfectly in the hearing protection, so i had minimal customizing that needed to be done here.
You want to remove all the foam padding in the hearing protection to install the electronics, you will not need all of it again, since the electronics is going to take up a lot of the space. The only thing we are going to use from the headphones is the speakers in them.
Once the headphones and the hearing protection have been disassembled, we are ready to install the electronics.
Let's go to the next step! :)
Step 2: The Electronics
Sorry for missing pictures of the installation process, i completely forgot to take any, and it only took a few minutes.
I would recommend installing the battery first, because it is the biggest part so if you install the smaller parts first, you might not be able to fit the battery. I used a 18650 Li-Ion cell, but any 3.7V Li-Ion can be used.
After installing the battery in the casing, install the rest of the electronics so you can still fairly easily access the terminals you need to solder wires to. You could also solder everything together first, but it makes it harder to install, because the space is very limited.
make two small holes in the top of both the left and right casing of the hearing protection for the wires to the speakers. Solder the wires from one of the speakers and route it though the holes. I installed my electronics in the left casing, so the wire to the right speaker is routed out through the hole i the left casing, and in through the hole in the right casing, and then resoldered to the speaker. Twist the wire round the headband so it looks tight, but not so tight that you can't adjust them.
The speakers are connected to the bluetooth module via the minijack that was already on them. (this was the easiest way to do it, since my bluetooth module already had a minijack output)
I connected the battery via an SPDT switch, so the circuit has a "play-mode" where the bluetooth module gets the power from the battery via the step-up while the charge controller is disconnected, and a "charge-mode" where you cannot play music with them, but only charge them. The "charge-mode" also works as "OFF-mode" when not connected to a charge source.
It is not really necessary to use the 3-5v -> 5v step-up, as the bluetooth module runs ok without it, but it does have a bit more noise in the music when you do not use it, and i find it extremely annoying.
I've included a wiring diagram above that should show in detail exactly how i have wired the electronics, and you will probably get much more info from looking at that, than me describing how it is done :)
Step 3: Re-assembling
Once you have connected all the electronics, test it before you close everything off! it sucks having to rip it all apart because you have a loose connection or a bad solderjoint, and it doesn't work. When you have tested it, and it works, you can close it off.
stuff the foam you took out back in the casing, but not too much because the electronics CAN overheat, although none of the units get particularly warm during use (i've tested both the charging and play mode for 3 hours each, without any major heat issues).
Mount the speakers on top of the foam, and fasten them with the hot-glue gun. Once the glue sets, put the ear-protection back on, and you are done. Make sure to make them as airtight as possible.
Enjoy your new awesome noise-cancelling bluetooth headphones! :D
If you liked it, you can vote for my instructable in the "Little Bits tech contest" :)
Step 4: Further Addons and Ideas
One thing this really needs, is a kind of battery indicator, so you don't run out of power while on the road because you forgot to charge. It could be done with something as simple as a single LED to indicate low voltage.
It could also be nice with something to indicate when the headphones are in "play-mode" so you don't forget to turn them off. This would be logical to implement along with the battery indicator.