Hooking up more than one infrared thermometer to the IOIO

images are CC BY-NC-SA 3.0
This demo assumes that you are familiar with the MLX90614 and the IOIO or that you have seen the Hooking up one infrared thermometer to the IOIO demo.

For you to be able to connect more than one sensor to an I2C protocol, you need to be able to address each sensor individually. This is done by using the sensor's individual address. The problem with these thermometers is that from the factory they come with the same address (0x5A) so you need to be able to change that address. I don't go into this yet because it actually took me a few days to figure out how to do it and I'm not yet sure I have a handle on it.

That will be a future demo.


  • More than one MLX90614 Sensor
  • IOIO OTG Board
  • an Android device
  • USB or BT connection to your Android device
  • Power source for the IOIO
  • 6- 4.1K resistors
  • circuit cables
  • Bread Board



First you must build your circuit.
Pinout map from Datasheet

The wiring for this is very simple. The sensor has 4 pins that will connect to power (3v) and ground; and to the SCL and SDA wires for the I2C (more on this later).

Circuit Drawing

The power wire connects directly to pin 3 of the sensor and connects in parallel to each of the resistors.
Pin 4 goes directly to ground.
Pin 1 goes to one of the resistors and to pin 5 on the IOIO.
Pin 2 goes to the other resistor and to pin 4 on the IOIO.

This circuit is not difficult but since there will be more than one thermometer, you must be extra careful with your cables and connections.


public class TempSensingMain extends IOIOActivity {
  private final String TAG = "TempSensingMain";

  //Sensor I2C
  private TwiMaster twi;
  double sensortemp;

  private TextView TempCelsius1;
  private TextView TempFahrenheit1;
  private TextView TempCelsius2;
  private TextView TempFahrenheit2;
  private TextView TempCelsius3;
  private TextView TempFahrenheit3;

Declaration of the TwiMaster interface and other variables. Also one text per sensor.

  public void onCreate(Bundle savedInstanceState) {

    TempCelsius1 = (TextView) findViewById(R.id.tempC1);
    TempFahrenheit1 = (TextView) findViewById(R.id.tempF1);
    TempCelsius2 = (TextView) findViewById(R.id.tempC2);
    TempFahrenheit2 = (TextView) findViewById(R.id.tempF2);
    TempCelsius3 = (TextView) findViewById(R.id.tempC3);
    TempFahrenheit3 = (TextView) findViewById(R.id.tempF3);

Initializing the TextViews

  class Looper extends BaseIOIOLooper {

    protected void setup() throws ConnectionLostException {
      twi = ioio_.openTwiMaster(0, TwiMaster.Rate.RATE_100KHz, true);
      //InitSensor(0x00, twi);

    public void loop() throws ConnectionLostException {
      try {
        ReadSensor(0x34, twi);		//dec 52
        ReadSensor(0x2a, twi);		//dec 42
        ReadSensor(0x5a, twi);		//dec 90

      } catch (InterruptedException e) {

This is a key step! Each sensor needs to have a different address so that it can be accessed by the IOIO. the default address is 0x5A but the other addresses need to be set manually. I don't yet have the code to do this. I used the code from Connecting Infrared Thermometer MLX90614 to Wiring and used an Arduino to do this. However, the address was not the number I wanted so my sensors were los for a while and I had to write a loop that would go through every address and look for a response until a found the valid addresses.

  protected IOIOLooper createIOIOLooper() {
    return new Looper();

  public void ReadSensor(int address, TwiMaster port) {

    byte[] request = new byte[] { 0x07 }; //Byte address of sensor data
    byte[] tempdata = new byte[2];        //Byte to save sensor data
    double receivedTemp = 0x0000;         //Value after processing sensor
    double tempFactor = 0.02;             //0.02 degrees per LSB 
                                          //(measurement resolution of 
                                          // the MLX90614)

    byte[] getAddress = new byte[] { 0x6f };
    byte[] getByte = new byte [2];

    try {
      port.writeRead(  address,

      receivedTemp = (double)(((tempdata[1] & 0x007f) << 8)+ tempdata[0]);
      receivedTemp = (receivedTemp * tempFactor)-0.01;

      handleTemp(address, receivedTemp);

    } catch (ConnectionLostException e) {
      // TODO Auto-generated catch block 
    } catch (InterruptedException e) {
      // TODO Auto-generated catch block

This method reads the temperature from each sensor according to their address. The memory location where the data resides is 0x07 and it returns 2 bytes 'tempdata[0] and tempdata[1]' that are arranged and multiplied by the 'tempFactor'. The final number is sent to 'handleTemp' to finally display the value.

  private void handleTemp (double address, double temp){

    final float celsius = (float) (temp - 273.15);

    final float fahrenheit = (float) ((celsius*1.8) + 32);

    switch ((int)address){
    case 90:
      TempCelsius1.post(new Runnable() {
        public void run() {
          TempCelsius1.setText("Celsius 1: "+ celsius);
          TempFahrenheit1.setText("Fahrenheit 1: "+ fahrenheit);
    case 42:
      TempCelsius2.post(new Runnable() {
        public void run() {
          TempCelsius2.setText("Celsius 2: "+ celsius);
          TempFahrenheit2.setText("Fahrenheit 2: "+ fahrenheit);
    case 52:
      TempCelsius3.post(new Runnable() {
        public void run() {
          TempCelsius3.setText("Celsius 3: "+ celsius);
          TempFahrenheit3.setText("Fahrenheit 3: "+ fahrenheit);

This method creates runnables to pass the value to the UI thread and update the view.