Dec 282020

So, a while back I tore apart an old Logitech wireless headset with the intention of using its bits to make a wireless USB audio interface. I was undecided whether the headset circuitry would “live” in a new headset, or whether it’d be a separate unit to which I could attach any headset.

I ended up doing the latter. I found through Mouser a suitable enclosure for the original circuitry and have fitted it with cable glands and sockets for the charger input (which now sports a standard barrel jack) and a DIN-5 connector for the earpiece/microphone connections.

The first thing to do was to get rid of that proprietary power connector. The two outer contacts are the +6V and 0V pins, shown here in orange and white/orange coloured cable respectively. I used a blob of heat-melt glue to secure it so I didn’t rip pads off.

Replacing the power connector. +6V is orange, 0V is orange/white.

The socket is “illuminated” by a LED on the PCB. Maybe I’ll look at some sort of light-pipe arrangement to bring that outside, we’ll see.

The other end, just got wired to a plain barrel jack. Future improvement might be to put a 6V DC-DC converter, allowing me to plug in any old 12V source, but for now, this’ll do. I just have to remember to watch what lead I grab. Whilst I was there, I also put in a cable gland for the audio interface connection.

Power socket and audio connections mounted in case.

One challenge with the board design is that there is not one antenna, but two, plus some rather lumpy tantalum capacitors near the second antenna. I suspect the two antennas are for handling polarisation, which will shift as you move your head and as the signal propagates. Either way, they meant the PCB wouldn’t sit “flat”. No problem, I had some old cardboard boxes which provided the solution:

PCB spacer, with cut-out for high-clearance parts.

The cardboard is a good option since it’s readily available and won’t attenuate the 2.4GHz signal much. It was also easy to work with.

I haven’t exposed the three push-buttons on that side of the PCB at this stage. I suppose drilling a hole and making a small “poker” to hit the buttons isn’t out of the question. This isn’t much different to what Logitech’s original case did. I’ll tackle that later. I need a similar solution for the slide-switch used for power.

One issue I faced was wrangling the now over-length FFC that linked the two sides. Previously, this spanned the headband, but now it only needed to reach a few centimetres at most. Eyeballing the original cable, I found this short replacement. I’ll have to figure out how to mount that floating PCB somehow, but at least it’s a clean solution.

Replacement FFC.

At this point, it was a case of finish wiring everything up. I haven’t tried any audio as yet, that will come in time. It still powers up, sees the transceiver, so there’s still “life” in this.

Powering up post-surgery.

I plugged it into its charger and let it run for a while just to top the LiPo cell.

Charging for the first time since mounting.

One thing I’m not happy with is the angle the battery is sitting at, since it’s just a bit wider than the space between the mounting posts. I might try shaving some material off the posts to see if I can get the battery to sit “flat”. I only need about 1mm, which should still allow enough clearance for the screwdriver and screw to pass the cell safely.

The polarity of the speakers is a guess on my part. Neither end seemed to be grounded, hopefully the drivers don’t mind being “common-ed”, otherwise I might need to cram some small isolation transformers in there.