Bluetooth

Bluetooth implementation on the micro:bit

Overview

The micro:bit processor has an on-board Bluetooth transceiver. This is combined with a PCB trace aerial and other minor components alongside a software stack that gives the micro:bit a certified and credible Bluetooth capability.

Bluetooth software stack

V1 Nordic Semiconductor Soft Device S110 V2 Nordic Semiconductor Soft Device S113

Using Bluetooth, you can connect to other devices and send and receive data from and to the micro:bit.

Bluetooth is distinct from the micro:bit to micro:bit radio feature,which is a proprietary protocol from Nordic and Lancaster University.

BBC micro:bit Bluetooth Profile

The micro:bit supports Bluetooth via a single, custom-developed, BBC micro:bit profile. This profile allows it to communicate with other BLE capable devices.

CODAL

A pre-compiled hex file is available to download for V2 that enables all Bluetooth services.

Bluetooth all services CODAL

The source for this can be found in the [microbit-v2-samples]https://github.com/lancaster-university/microbit-v2-samples/tree/master/source/samples repository.

DAL

The BBC micro:bit V1 Bluetooth profile is defined in the DAL

You can flash one of two pre-compiled Hex files to the micro:bit V1 that enable bluetooth services. As Bluetooth is memory intensive, these are supplied as either ‘without Magnetometer Service’ or ‘without DFU Service’:

Without magnetometer

Without DFU

The DAL contains the C++ source for the BLE service files

There are also some example programs in the microbit-samples repository:

The micro:bit has a V2Bluetooth 5.0/V1Bluetooth 4.1 stack with Bluetooth Low Energy (BLE) and supports the V1GAP Peripheral Role and V2 GAP Peripheral and Central device roles.

It operates in the ISM (Industrial Scientific Medical) band, as per all Bluetooth devices. This starts at 2.4GHz and ends at 2.41GHz. BLE divides the frequency band into 50 x 2MHz bands of which 40 are used. These are called channels and numbered 0 to 39. Channels 37, 38 and 39 are used for “advertising”.

When devices are connected, they use the other channels in a particular sequence controlled by a feature called adaptive frequency hopping. This helps reduce the impact of congestion from other radio users.

Data transfer rates will only be a few hundred Kilobytes per second at best, and throughput depends on how your application uses the Bluetooth features. Throughput depends on the proportion of system protocol overheads to application data. Lots of small packets containing - for example - temperature data would have a lower data transfer rate than using the UART service.

There are some useful advanced configuration options in the micro:bit runtime code

Challenge

It would be possible for anyone with the appropriate knowledge to define and implement other Bluetooth profiles.

We are seeking collaborators to help us define the new profile elements that expose some of the V2 features.

Further information

Bluetooth and the micro:bit software

The DAL/C++ reference documentation lists the adopted and custom features available within the profile. MakeCode contains a set of blocks to make use of the various micro:bit services.

The processor also has several non-bluetooth, proprietary modes of operation upon which the micro:bit radio protocol is based. This protocol works only between micro:bits and is defined as ‘Micro:bit Radio’ in the DAL and ‘radio’ in MakeCode, MicroPython, and Mbed C++.

Apps