BLE Log Service

Extension for Bluetooth retrieval and modification of the micro:bit v2 data logger's log.

Enabling the service

blelog.startBLELogService(passphrase?: string) : void

Start the BLE Log service (with optional passphrase). This should be included in the start blocks.

If a passphrase is empty, no passphrase is required for other devices to retrieve data. If a passphrase is provided, devices must provide the passphrase to retrieve the data over Bluetooth. (The passphrase does not impact access to the data log file on the micro:bit). If a passphrase is longer than 20 characters, only the first 20 characters are used.

Example

blelog.startBLELogService()

Retrieving Data

Currently data can be retrieved by a browser based client (currently Chrome and Edge only): https://bsiever.github.io/microbit-webblelog/.

A JavaScript library is available to develop User Interfaces, etc.: https://github.com/bsiever/microbit-webblelog

Students at Michigan Tech developed a Web App to Collect and Graph Data! Live Site! (code)

Bluetooth Service Overview

Service UUID

accb4ce4-8a4b-11ed-a1eb-0242ac120002

Characteristics

Security

Read/notify will indicate a true (0xFF) if the interactions are authorized and false (0x00) otherwise. (Automatically sends value when notifies are enabled)

If false, a correct passphrase is required to enable access to other data.

Passphrase

Characteristic to write passphrase (if needed). If a passphrase is required and the correct one is provided, other characteristics will be available. Access will be granted until disconnection.

The passphrase that is required can be provided in the blelog.startBLELogService() block. By default (empty passphrase) a passphrase will not be required. Passphrases are no more than 20 characters.

Data Length

The length of the data in bytes (uint32_t).

Data

Notifiations will be 0-20 bytes. An empty (length 0) indicates the end of transmitted data. If non-empty, the first 4 bytes are the index into the message and the remaining bytes are the data starting at that index (up to 16 bytes of data).

Data Request

Two uint32_ts:

• A uint32_t indicating the index into the log to retrieve.
• A uint32_t indicating the length (in bytes) to retrieve.

Data is sent via the Data characteristic notifications (accb53ba-8a4b-11ed-a1eb-0242ac120002)

Erase

Write the full word "ERASE" to erase the log file. (It only erases if authorized)

Usage

10 times the percentage of log currently in use (uint16_t from [0-1000], where 1000=100.0).

Time

The current micro:bit clock (milliseconds) as a uint64_t.

Acknowledgements

Icon based on Font icon 0xF147 SVG.