TI SensorTag

Overview


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.

Necessary Modifications

 * 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)

$hciconfig hci0 up  $hciconfig 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
 * Retrive the BLE Address of your sensorTag. Press the side button on your sensorTag so that it enters discovery mode.

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  client.close os.remove( soc_fd ) raise except: pass
 * Modify sensortag.py with your given bluetooth_adr (see main), socket communication code, and 2's complement code.


 * Modify BoneServer.js by appending said code:

function sensorInit( socket ) {  /////////////////////////////////////////////////////////////////////////////       // Executing Python script that communicates with Sensortag /////////////////////////////////////////////////////////////////////////////       var net = require('net'); // upon connection to ballAndCube.js via 'SensorTag' message, run sensorTag python script socket.on('SensorTag', function {             // This server listens on a Unix socket at /tmp/py_soc            var unixServer = net.createServer(function(client) { // Send data as it's recieved  client.on( 'data', function(data) {                   var chunk;                    // Prints recieved data to console                    //console.log ("data: ", data.toString );                    socket.emit( 'SensorTag', data.toString );                } ); client.on('end', function {                   console.log('client disconnected');                }); });            //location of the python socket as specified in sensortag.py             unixServer.listen('/tmp/py_soc');             // EXEC python sensortag.py at given location (NOTE SPECIFIC TO YOUR LOCATION)            var exec = require('child_process').exec, child;            child = exec(  '~/ece497/exercises/realtime/sensortag.py' , function ( error, stdout, stderr) { console.log( stdout ); if (error !== null) { console.log('exec error: ' + error ); }	           } );        } );    } Upon receiving a 'SensorTag' message, the above code initializes a Unix socket server and the sensortag.py script. The SensorTag message comes from ballAndCube.js

io.sockets.on('connection', function (socket) {       ...        sensorInit(socket)        ...    }
 *  Call sensorInit  in body of

//Global Varibles added var Gx = 0, Gy = 0, Gz = 0; var Ax = 0, Ay = 0, Az = 0; var lastX = 300*0.5 - 50; var lastY = 300*0.5 - 50; var WIDTH = 800, HEIGHT = 600; var ENABLED_ACC = 1; var ENABLED_ACC_Y = 0;
 * 'Modify BallAndCube.js to include your BLE initialization and callbacks:

function connect { if(firstconnect) { ...      socket.on('SensorTag', sensorTagParse ); // SensorTagParse is my callback for any SensorTag Data socket.emit( 'SensorTag' ); ...

function animate { // note: three.js includes requestAnimationFrame shim requestAnimationFrame(animate); cube.position.y = lastY + 0.1*Ay; cube.position.x = lastX + 0.1*Ax; '''//Bind the cube to displaying within the frame if (cube.position.x > WIDTH/2 ){ cube.position.x = WIDTH/2; }       if (cube.position.x <  -1*WIDTH/2 ){ cube.position.x = -1*WIDTH/2; }       if (cube.position.y > HEIGHT/2 ){ cube.position.y = HEIGHT/2; }       if (cube.position.y < -HEIGHT/2 ){ cube.position.y = -HEIGHT/2; }       lastX = cube.position.x;        lastY = cube.position.y;        //console.log( "lastX = " + lastX ); cube.rotation.y = cube.rotation.y + 3.14159*Gy/250; cube.rotation.x = cube.rotation.x + 3.14159*Gx/250; cube.rotation.z = cube.rotation.z + 3.14159*Gz/250; renderer.render(scene, camera); }

function sensorTagParse( data ) { var gData, maximum; // check if received data is valid  if(data.value !== "null") { gdata = data.split(" ") '''// Data is in format "[ ID, X, Y, Z ] " switch( gdata[0] ) { case "G": // We want a log funct to diminish effect of extreme measurements, but still record // 11.09... is log( 2^15), so we are converting back to signed  var y_tmp = (Math.log( gdata[1] ) - 11.09035489) * 100 ; if ( Math.abs(y_tmp) < 3 ){ '''// if measurement is insignificant, set to zero (i.e. calibrating) Gy = 0; } else { if ( y_tmp < 0 ){ '''// if measurement is negative, move in the negative direction. Also cap max # of pixels moved at a time ''' Gy = Math.max( y_tmp, -1) * 1.5; } else { Gy = Math.min( y_tmp, 1) * 1.5; '''// it's positive. also cap max number of pixels moved at a time''' }                   }                // repeat the above process but for x var x_tmp = (Math.log( gdata[2] ) - 11.09035489) * 100 ; if ( Math.abs(x_tmp) < 0.8 ) { Gx = 0; } else { if ( x_tmp < 0 ){ Gx = Math.max( x_tmp, -0.5) * 3; } else { Gx = Math.min( x_tmp, 0.5) * 3; }               }                // repeat the above process but for z var z_tmp = (Math.log( gdata[3] ) - 11.09035489) * 100 ; if ( Math.abs(z_tmp) < 3 ) { Gz = 0; } else { if ( z_tmp < 0 ){ Gz = Math.max( z_tmp, -1) * 1.5; } else { Gz = Math.min( z_tmp, 1) * 1.5; }               }                  //console.log( "Gx = " + Gx + " Gy = " + Gy  + " Gz = " + Gz) ; break; case "A": if (ENABLED_ACC ){ var ax_tmp = gdata[1] if ( ax_tmp < 0 ){ Ax = Math.max(ax_tmp*1000, -40); } else { Ax = Math.min(ax_tmp*1000, 40); }                   var ay_tmp = gdata[2] - 0.109375; if ( ENABLED_ACC_Y ){ if ( Math.abs(ay_tmp) > 0.02 ){ if ( ay_tmp < 0 ) { Ay = -1* Math.max(ay_tmp*100, -40); } else { Ay = -1* Math.min(ay_tmp*100, 40); }                        } else { Ay = 0; }                    }                    Az = gdata[3]; console.log( "Ax = " + Ax + " Ay = " + Ay + " Az = " + Az) console.log( "Cposx = " + cube.position.x ) break; }           }        }        status_update("\" + "live" + "\"");    }

Communication Flow


hciconfig hci0 up
 * The program is initialized by

$ ./boneServer.js


 * As the sever initializes, point your browser to the web server on your beagle (i.e 192.168.7.2:9090)
 * Click on the ballAndCube image
 * Wait for communication scripts to initialize
 * You may need to press the side button on your sensorTag for the dongle and the sensorTag to 'discover' each other, and pair

Debug
Error: listen EADDRINUSE your socket may already be in use/binded to another instance of gattool. To resolve: $ rm /tmp/py_soc #or whatever address you've mapped your socket too
 * If you get
 * You may notice that the resolution of measurements is not too good, this is due partly in fact to the sensor refresh rate of 1Hz (1 sample/sec is transmitted). This can be resolved by changing the sensorTag firmware.