example for I2C sensor reading about crossbar-examples HOT 5 CLOSED

switch(command){
  case 0x01: // LED Blink Command
    if(argc < 3) break;
    byte blink_pin;
    byte blink_count;
    blink_pin = argv[0];
    blink_count = argv[1];
    delayTime = argv[2] * 100;
  argv[1] = 22;
    pinMode(blink_pin, OUTPUT);
    byte i;
    for(i = 0; i < blink_count; i++){
      digitalWrite(blink_pin, true);
      delay(delayTime);
      digitalWrite(blink_pin, false);
      delay(delayTime);
    }
    Firmata.sendSysex(command, argc, argv); // callback
    break;

arduino.sysex(0x01, [22, 6, 6], function(r2) { 
    arduino.on('sysex', function(e){
    console.log("Data 2: ", e.command);
    console.log("data    : " + JSON.stringify(e.data));

var device_port = '/dev/ttyATH0';
var firmata = require('arduino-firmata');
var arduino = new firmata();
arduino.on('connect', function(){
  arduino.pinMode(3, firmata.PIN_MODE_I2C);
  arduino.pinMode(2, firmata.PIN_MODE_I2C);
  arduino.sysex(0x78);  // 0x78 = I2C_CONFIG
  arduino.sysex(0x76, [0x58, 'I2C_READ'], function(x){   //0x76 = I2C_REQUEST
      arduino.on('sysex', function(e){
    console.log("Data: ", e.command);
     console.log("data    : " + JSON.stringify(e.data));
  });
  });
   console.log("connected");
});

arduino.connect(device_port);

Wire.beginTransmission(hytaddr[i]); // Begin transmission with given device on I2C bus
      Wire.requestFrom(hytaddr[i], 4); // Request 4 bytes
      // Read the bytes if they are available
      // The first two bytes are humidity the last two are temperature
      if(Wire.available() == 4) 
      {
        int b1 = Wire.read();
        int b2 = Wire.read();
        int b3 = Wire.read();
        int b4 = Wire.read();
        Wire.endTransmission(); // End transmission and release I2C bus
        // combine humidity bytes and calculate humidity
        int rawHumidity = b1 << 8 | b2;
        // compound bitwise to get 14 bit measurement first two bits
        // are status/stall bit (see intro text)
        rawHumidity = (rawHumidity &= 0x3FFF);
        humidity = 100.0 / pow(2,14) * rawHumidity;
        // combine temperature bytes and calculate temperature
        b4 = (b4 >> 2); // Mask away 2 least significant bits see HYT 221 doc
        int rawTemperature = b3 << 6 | b4;
        temperature = 165.0 / pow(2,14) * rawTemperature - 40;