October 29, 2022

A building-block for DIY Bluetooth audio devices

I’m a late adopter of Bluetooth, having previously tried Bluetooth in its earlier days, hearing something that sounded like my music was being fed down a drain pipe, and deciding that Bluetooth was rubbish… it wasn’t until I bought a Logitech H830 headset that I found that Bluetooth can actually sound decent… moreover when I bought the Logitech Zone Wireless, that bi-directional Bluetooth can also sound decent.

Now, the Zone Wireless is fine if I’m in the office, or out walking somewhere. It’ll fit underneath the coolie hat if I decide to wear that, otherwise it works with a cap just fine. BUT, if I’m camping or at a WICEN event, I’m often wearing a full-brim hard hat. The headband on the Zone Wireless is a problem.

I really wanted a Bluetooth device that could be put on a lanyard, and I just plug in a regular common-garden variety wired headset. The closest I can get to this is a motorcycle headset — as these have to accommodate a wide variety of helmet styles, the radio module and the headset are actually separate components, and so conceivably, I can make my own compatible adaptor to plug in. Then, it wouldn’t matter… want to wear the hard hat? No problem, I already have modded earmuffs with a headset. Want to use it on the bike? Sure, plug the helmet straight in. Or am I in the office again? No problem, normal headset.

It’d also be nice to share that wired headset with a wired audio device… prime example here is a radio transceiver. Yes, there are devices that will make those do Bluetooth… and there are radios that have Bluetooth. I had one of the latter: Yaesu VX8-DR … it’s Bluetooth was next to useless… idiosyncratic and unreliable.

I see the Sena SR-10 mentioned in a few places as a way to “Bluetooth-enable” a two-way radio… but aside from being pricey, I see three complaints being raised: unreliable/slow pairing, intermittent darlek-like distortion on transmit and a noticeable connection delay on incoming signals.

I pondered doing my own… and I’ve slowly amassed parts to do exactly that. But, the other day, I stumbled on another option: Altronics sell a CSR8635 Bluetooth module. This advertises the ability to talk to two Bluetooth devices, and wideband voice. CSR’s own datasheet seems to give some hints as to how it can be used.

One catch, is the pads on this device are a 1mm spacing — so mounting this on some perfboard is going to be a big challenge. I prefer the minimalism of a module like this over a Raspberry Pi Zero W… a lot less to go wrong, and likely much better battery life.