TI SensorTag

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BBB interfaceing with Adafruit's BLE Module

The TI BLE SensorTag is a portable low-power module that uses Blueooth Low Energy (BLE, Bluetooth 4.0) and various sensors to communicate data to any BLE reciever.

TI Sensortag Wiki

The python scripts that interface with the BeagleBone Black were gently modified from msaunby's Raspberry Pi Scripts.

System Outline

  • The Beaglebone Black runs BoneServer.js which creates a webserver on port 9090.
  • The user selects the ballAndCube picture, which launches ballAndCube.html, ballAndCube.js, and the sensortag.py locally on the server (i.e. the BLE dongle is connected to the server not the client).
  • The sensortag.py python script outputs data, which is handled as an event streamer by node.js, to stream the data to ballAndCube.js which renders object, and interprets the Gyroscope/Accelerometer Data.
  • Since the python script, which uses gattool, runs in its own process, the data that it receives is streamed without buffering to the client's ballAndCube.js script.

Before You Start

  • Retrieve the original python BLE scripts from this github repo.
  • Execute the sensortag.py script to determine if it executes properly (i.e. your linux distribution comes with pexpect); if not, retrieve pexpect online (I used v3.2)
  • Retrive the BLE Address of your sensortag
  $hciconfig hci0 up
  hci0: ...
        UP RUNNING
  $hcitool lescan
  LE Scan ...
  90:59:AF:0B:84:57 (unknown)
  90:59:AF:0B:84:57 SensorTag
  ^^^ Is the BLE address of your sensorTag
  • Modify sensortag.py with your given bluetooth_adr (see main), socket communication code, and 2's complement code.
   import socket
   import os, os.path
   # 2's complement as per StackOverflow post
   def twos_comp(val, bits):
        """compute the 2's compliment of int value val"""
        if( (val&(1<<(bits-1))) != 0 ):
            val = val - (1<<bits)
        return val
   # In accelerometer function
   # User "client.send( )" instead of print, to send data to your node.js server
   client.send( "A " + str(xyz[0]) + " " + str(xyz[1]) + " " + str(xyz[2]) )
   # the "A", serves as a tag to distinguish between each of the sensors
   # In gyroscope function
   # join two bytes to form 16 bit number, make unsigned.
   dx = twos_comp(  (  (v[1]<<8) + v[0] ) , 16 ) + 65536 
   dy =  twos_comp(  (  (v[3]<<8) + v[2]  ), 16 ) + 65536
   dz =  twos_comp( (  (v[5]<<8) + v[4]  ), 16 ) + 65536
   client.send( "G " + str( dx )+ " " + str( dy ) + " " + str(dz)  )
   # In main():
   global client
   soc_fd = "/tmp/py_soc" 
   # ^^ Unix socket file that python makes, modify as necessary
   client = socket.socket( socket.AF_UNIX, socket.SOCK_STREAM )
   client.connect( soc_fd )
   # ^^ sets up a Unix stream socket @ soc_fd (see socket man pages)
   # comment out any sensor init code for sensors you don't wish to use
   except (KeyboardInterrupt, SystemExit):
        # cleanup code 
       os.remove( soc_fd )

Communication Flow


Sample C Code

#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <poll.h>
#include <signal.h>
#include <unistd.h>