Before finding the handy Bluetooth receiver I considered repurposing old handsfree unit I had used ages ago. The exact model is Jabra BT205, maybe from ten years ago or so. I never managed to get comfortable with this type of hands-free unit so eventually I just got a car radio with built-in Bluetooth hands-free. Much much better.
Now that I thought about getting rid of wires for hearing protector I actually considered if this could be used. It naturally doesn't have the newer audio codec in it, just the original voice-only codec of original Bluetooth specification, but quality still might be tolerable for audiobook use.
Before tearing this down I tried charging it. Completely dead. Guess ten years of inactivity wasn't good for the lithium battery pack. I already had some doubts on whether this could be adapted to work with 2 AA batteries (that the hearing protector uses) but decided to go in anyway.
After some careful attempts the device came apart nicely. Electronics and battery are inside another plastic module, and connected to battery, charging port, microphone and headphone with wires.
Opening inner plastic was easy enough and I could access the PCB. Nothing surprising there, main Bluetooth chip (in middle) and assorted components elsewhere. Here earpiece wires go to left (best guess that chips near it are amplifier), microphone to up (I might have pulled wires enough to expose copper when opening it), battery down and charge port wires top right.
On the right side of the battery wires, at the bend you can see exposed (gold-colored) copper at the edges of the PCB with curious loop connecting them. This would be the 2.4GHz antenna. The copper on edge extends to both sides and bottom of PCB too; I'm somewhat curious on the process how they have managed to make this work, as cutting the shaped PCB off the larger board often destroys traces too near the cutting edges. Must be some kind of post-cut process I've never heard of.
Main chip is CSR BC215, which from basic search seems to be (unsurprisingly) made-for-the-job chip. As usual for many old chips, finding proper datasheet for this seems to be a bit difficult (I don't specifically need that data so no real effort wasn't spent on trying to find it). No proper datecode on any chips either, so I'll just settle on that earlier ten-year guess.
Now, on the bad things. While the board still works and connects to my phone easily enough (and music quality was as bad as I expected), as it is designed to work with lithium battery (i.e. about 3.6v nominal), there is no way to get it to work with just 2 AA batteries of hearing protector; when lowering the voltage it turned itself off at about 2.8 volts, way too high for 2 AAs.
So this is about as far as I got. Unless I come up with something else, there is no point going any further with this for now.
But before that I have to mention the charger too. This being fairly old device it comes with a special dock onto which HF is dropped in to be charged. On other side there is fairly standard (of that time) round power plug, albeit with less standard 6v voltage. In this picture I had already opened it so PCB is visible. The three contacts are for charging; voltage in middle, two ground pins on the sides.
Remember, this was long before (almost) everyone settled into USB charging (and back then USB connectors were huge for device like this, no microUSB yet!) so this isn't too weird.
Inside was pretty much as I expected. Well, almost, I expected to find just wires between power plug and charger pins but surprisingly there's actually a PCB in there!
And in trash it goes. The charger I mean, earpiece PCB itself might prove handy someday so that'll I keep. At least for a while.
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