I have a hate-love relationship with Bluetooth. I would like to like it, but it always turns out to be frustrating. The idea of having a short-range wireless standard which allows coupling devices to each other is great. And on humble days I find it amazing that it works to the extent that it does.
Bluetooth has long been what USB is becoming, namely an opaque mess of incompatible devices where a layperson cannot determine whether they will be compatible beforehand. The box will only say “Bluetooth”, perhaps something like “Bluetooth 4.2”, but what does this really mean?
My latest frustrating example is with my bluetooth keyboard and my TV. My TV has already successfully paired with my headphones, and my phone can pair with the headphones and the keyboard. But the TV cannot pair with the keyboard. In order to see whether they had a theoretical chance to work with each other, I looked up the Bluetooth versions:
|Laptop||Lenovo ThinkPad X220||3.0|
|Phone||Xiaomi Mi A1||4.2, A2DP, LE|
|Tablet||Samsung Google Nexus 10||3.0, A2DP|
|Tower PC||Mpow Bluetooth||5.0|
From this table I see that the TV and the phone have the same bluetooth version, so why does the keyboard work with the smartphone but doesn't work with TV?
I installed an app on the phone to get a bit more information about the Bluetooth support. The TV has type Dual Mode – BR/EDR/LE. A Reddit post really helped me here. There are two completely parallel Bluetooth standards, the Classic and Low Energy modes. The latter is this LE, whereas the former is BR and EDR, which stand for Basic Rate and Enhanced Data Rate. The TV apparently has a dual radio built in. And then it also supports the Advanced Audio Distribution Profile (A2DP) in both directions as well as Audio/Video Remote Control Profile (AVRCP). The keyboard has just a Classic radio with BR/EDR. It only supports the Human Interface Device (HID) profile.
The TV doesn't explictly list HID, but as a mere client, it likely doesn't list that. And the TV explicitly has a system settings menu to couple keyboard and mice, so it is definitely intended to use it.
My laptop, which supports the keyboard, has just a Classic BR/EDR radio and suuports A2DP in both directions, and the Headset Profile (HSP). There is no HID profile either, so it apparently isn't needed to use the keyboard.
At this point, I am totally at loss why the TV doesn't recognize the keyboard. If I'd contact the support of either company, their first level support would just give me some random answer effectively stating that the other manufacturer's product just doesn't implement Bluetooth the right way. We are already at the same state that we have with USB-C: Plug it in, and if it doesn't work, it might be on either end of the cable, or actually the cable itself. You have little chance to reliably see whether it works beforehand.