RPi Bluetooth LE

From eLinux.org
Revision as of 13:05, 4 July 2017 by IanH (talk | contribs) (Add blescan and sensortag program guide)
Jump to: navigation, search

Bluetooth LE on the Raspberry Pi

The Raspberry Pi 3 has built-in support for Bluetooth Low Energy (BLE). BLE is the technology behind many fitness trackers and smartwatches, and allows small, low-power devices to transmit and receive information from a central computer or smartphone.

This tutorial gets you started with Bluetooth Low Energy using a Texas Instruments SensorTag - these are small, robust, relatively cheap and do interesting things out of the box. You can buy one directly from TI, or in the UK they are available from RS and Farnell.

Pre-requisites

Compatible Hardware

This page was written assuming the following hardware:

  • Raspberry Pi 3 Model B
  • Raspbian Jessie (April 2017), although later versions will probably work.
  • TI CC2650 SensorTag, firmware 1.30 (May 2016) or later

We'll also assume you are familiar with the basics of typing Bash commands using the command line.

Older models of the Pi should work with an external USB adapter. The author has used these two successfully:


Basic installation checks

The Pi 3's built-in Bluetooth adapter is called hci0. You can check it is operating correctly with the command:

hciconfig

This should show something like this:

hci0:	Type: BR/EDR  Bus: UART
	BD Address: B8:27:EB:23:E2:A4  ACL MTU: 1021:8  SCO MTU: 64:1
	UP RUNNING 
	RX bytes:1987 acl:0 sco:0 events:91 errors:0
	TX bytes:1647 acl:0 sco:0 commands:57 errors:0
 

If for some reason it is shown as DOWN you can re-enable it with:

sudo hciconfig hci0 up

Using the SensorTag

Scanning using hcitool

SensorTag with outer case removed

If you've not already done so, take a look at TI's Getting Started Guide which explains how to set up the SensorTag.

To wake it up, press the button on the left-hand side (see illustration) and the green LED should flash, once per second.

On the Pi, enter the command:

 sudo hcitool lescan

This will start a scan for any Bluetooth LE devices in range which are currently 'advertising'. You should shortly see something like this:

 pi@raspberrypi:~ $ sudo hcitool lescan 
 LE Scan ...
 B0:B4:48:ED:44:C3 (unknown)
 B0:B4:48:ED:44:C3 CC2650 SensorTag

Type Control-C to stop lescan. The 12 hexadecimal digits (B0:B4:48:ED:44:C3 in the example) are your tag's MAC address. You will need to know this when making Bluetooth LE connections to it.

Connecting with gatttool

The gatttool utility can make connections to Bluetooth LE devices. To try this, make sure the SensorTag's LED is flashing then run:

 gatttool -I -b MAC-address

where MAC-address is the value reported by hcitool (see above). gatttool will give you a prompt, ending [LE]>. Type connect to make a connection to the SensorTag. This is shown below:

 pi@raspberrypi:~ $ gatttool -I -b B0:B4:48:ED:44:C3
 [B0:B4:48:ED:44:C3][LE]> connect
 Attempting to connect to B0:B4:48:ED:44:C3
 Connection successful
 [B0:B4:48:ED:44:C3][LE]>

You can then type a number of commands. The primary command lists the available 'Services', which are groups containing 'Characteristics' - these are data items which can be read or written to the device. So, to read the device name you could use the char-read-uuid command, giving it the ID of the Bluetooth Device Name characteristic:

 [B0:B4:48:ED:44:C3][LE]> char-read-uuid 00002a00-0000-1000-8000-00805f9b34fb
 handle: 0x0003 	 value: 53 65 6e 73 6f 72 54 61 67 20 32 2e 30 

(These are the ASCII values for SensorTag 2.0.

The Sensortag User Guide at http://processors.wiki.ti.com/index.php/CC2650_SensorTag_User's_Guide lists all the available services and characteristics. For example, to turn on the optical sensor, we need to discover the 'handle' for the configuration characteristic (with ID f000aa72-0451-4000-b000-000000000000), then write an 0x01 byte to it:

 [B0:B4:48:ED:44:C3][LE]> characteristics 1 ffff f000aa72-0451-4000-b000-000000000000
 handle: 0x0046, char properties: 0x0a, char value handle: 0x0047, uuid: f000aa72-0451-4000-b000-000000000000
 [B0:B4:48:ED:44:C3][LE]> char-write-req 47 01
 Characteristic value was written successfully

In the example above the handle value was 0x47 (it may change with firmware versions). One the sensor is enabled, the light level can then be read from characteristic f000aa71-0451-4000-b000-000000000000:

 [B0:B4:48:BF:C9:83][LE]> char-read-uuid f000aa71-0451-4000-b000-000000000000
 handle: 0x0044 	 value: bc 0a 

In this example the light level bytes are bc 0a, and will change with the amount of light falling on the CC2650 device.


Using Bluetooth LE with Python

Installing bluepy

Using gatttool is very laborious for doing any useful work, so it's a good idea to use a programming language. The bluepy package is one way to use Bluetooth LE commands from Python - it can be installed from https://pypi.python.org/pypi using the pip command. If you don't already have pip, on the Pi or other Debian systems it is easily installed with:

 sudo apt-get install python-pip

Before installing bluepy you will also need some support libraries:

 sudo apt-get install libglib2.0-dev

Then you can run:

 sudo pip install bluepy

If successful, it will show a message such as this:

     Installing blescan script to /usr/local/bin
     Installing sensortag script to /usr/local/bin
 Successfully installed bluepy
 Cleaning up...

bluepy command-line programs

The blescan program performs a similar function to "hcitool lescan" but produces more information. You will need root privileges (using e.g. sudo) to run it. Typical output looks like this:

 pi@raspberrypi:~ $ sudo blescan 
 Scanning for devices...
     Device (new): b0:b4:48:ed:44:c3 (public), -68 dBm 
 	  Flags: <05>
 	  Incomplete 16b Services: <80aa>
 	  Complete Local Name: 'CC2650 SensorTag'
 	  Tx Power: <00>
 	  0x12: <08002003>
 	  Manufacturer: <0d00030000>

You can alter its behaviour with various command-line options; blescan -h gives help text.

The sensortag program connects to various versions of SensorTag, and reads their sensors. sensortag -h gives a full list of options; a typical run looks like this:

 pi@raspberrypi:~ $ sensortag -T -B B0:B4:48:ED:44:C3
 Connecting to B0:B4:48:ED:44:C3
 ('Temp: ', (26.84375, 21.3125))
 ('Barometer: ', (27.15, 1017.46))
 ('Temp: ', (26.875, 21.5625))
 ('Barometer: ', (27.15, 1017.48))
 ...

Use Ctrl-C to stop the program.

Using Bluetooth LE with Go (Golang)

Gatt is a Go package, which provides developers to create BLE applications for Linux and OS X.

Developers install Go language on the host machine, and cross-compile the applications for RPi.

The package accesses HCI devices directly via HCI sockets provided by BlueZ core (kernel space), so it doesn't require the BlueZ userland package.

To test the example programs (sample GATT server and clients):

Cross-compile the server example for an ARMv6 target device.

 GOARCH=arm GOARM=6 GOOS=linux go build examples/server.go
 cp server <target device>

Start the server on the target device

 sudo ./server

Cross-compile the client example (discoverer) for an ARMv6 target device.

 GOARCH=arm GOARM=6 GOOS=linux go build examples/discoverer.go
 cp discoverer <target device>

Run the discoverer to scan surrounding peripheral devices.

 sudo ./discoverer

Links: other Bluetooth Low Energy resources