How to switch off the need to pair your micro:bit when using Bluetooth

Pairing is the bedrock of all Bluetooth security. If you pair your micro:bit with your phone, for example, from that point on, only you can connect to and interact with your micro:bit. Imagine you were using your phone with my micro:bit Blue application to drive a  micro:bit controlled Kitronik buggy. You wouldn't want someone else connecting to it and driving it away, would you?

But not all applications need security. And pairing definitely impacts user experience. Furthermore, currently, whenever you flash a new hex file to your micro:bit, the pairing data gets wiped off your micro:bit so you have to 'forget' the pairing details on your phone and go through the entire pairing process again. Not great when you're performing develop/test cycles frequently.

Note: some changes are planned in this area. USB firmware is to be changed so that data on micro:bit, including pairing keys, will persist when new hex files are flashed. I'm also aiming to have a Block in Microsoft's PXT that lets you choose whether you want pairing or not and if you do, whether it should be based on the passkey system or Bluetooth's "Just Works" method. Watch this space for updates on both these developments.

If you're a micro:bit C/C++ developer, you can get under the hood in ways in which users of other tools often cannot. And this includes the ability to create a hex file which will result in your micro:bit not needing to be paired. Here's how.

In your project folder's root, you should have a file called config.json. All you need to do is ensure there's a property of the bluetooth json object called 'open' which has a value of 1. open=1 means 'no security'. Here's the first part of my config.json file:

{
    "microbit-dal": {
        "bluetooth": {
            "enabled": 1,
            "pairing_mode": 1,
            "open": 0,
            "dfu_service": 0,
            "event_service": 0,
            "device_info_service": 1
        },
        "gatt_table_size": "0x700"
    }
}

And that's it! Run 'yt clean' followed by 'yt build' and the resultant hex file will remove the need for your microbit to be paired when using Bluetooth.

Even with applications that need security, this is useful. You can do development and test cycles with pairing switched off, and enable it when you come to do your final testing and release build. The best of both worlds.

Use responsibly! :-)

Code it. Connect it. Bitty Software.