CoreBluetooth

March 13, 2018

In last post I wrote about bluetooth tracker app, that I have tried to create. The idea was to develop battery widget for iOS today’s screen, similar to standard one, just with one difference: it should show not only currently connected devices, but also keep track of previously synchronised.
I use AirPods every day, it’s very handy to always have a headphones in your pocket without need to unravel wires. They can play 3-4 hours by themselves, and charged then by case several times. The problem is that phone shows the battery level of case only when you open it and keep at least one ear piece inside, which in regular usage happened never. There is a LED inside, but with my poor eyesight I constantly got mixed up green with red on such small dot. Goal was to show last known battery status to all connected and previously connected devices, especially AirPods and their case. Work with Bluetooth in iOS is relatively simple and in detail described here. The Bluetooth framework called CoreBluetooth and to get battery level of surrounding devices you need to implement these steps:

• check for the state of CBCentralManager. It should be .poweredOn
• start scan for peripherals. For each found peripheral, CB evoke callback with RSSI number and array of advertisement data. This data usually contain device id, name, connected state and kCBAdvDataIsConnectable. I really hoped, that it is possible to get some information about battery at this point, but, actually, this is the last point, where I have got something from AirPods. Problem was, that they are stated as not connectable and next steps returned no results. And AirPods case doesn’t have any bluetooth at all, I hopped, that it served some host role between ear pieces.
• However, once scan is finished (it can be gone infinitely, but it drains battery very quick), it is possible to try to connect for founded devices.
• Connection failed? Get appropriate callback.
• If connection is successful, then successful callback is called and it is possible to try discover services, that this device is providing. Each bluetooth devices provide some list of services, each of them can be (in theory) found on bluetooth specifications.
• Last callback is called, when some services are found and it retrieves list of them. Each service contain UUID, i.e., battery service is 0x180F, and by using it it is possible to find actual value of battery on device.

Unfortunately, as I said, AirPods does not provide ability to connect them directly. May be I’m just missing some obvious point, but I have spend several hours trying to connect them, when in the end I decided to search in AppStore applications, that will find bluetooth devices nearby. None of them were able to provide more information, that I have found during debugging. I still think, that it should be possible somehow - AirPods can be connected to Android, after all, but after several wasted evenings I gave up. I have some more interesting ideas in mind.