Arduino and Multiple MLX90614 Sensors

 // remap_mlx90614.ino

 #include "i2cmaster.h"

 // New slave address, purposefully left shifted
 byte NewMLXAddr = 0x1B;
 // 0x5A is the default address - uncomment this to set it back
 // byte NewMLXAddr = 0x5A;

 void setup(){
   Serial.begin(9600);
   Serial.println("Setup...");
   // Initialise the i2c bus, enable pullups and then wait
   i2c_init();
   PORTC = (1 << PORTC4) | (1 << PORTC5);
   delay(5000);
   // Read current address bytes
   ReadAddr(0);
   // Change address to new value (NewMLXAddr);
   ChangeAddr(NewMLXAddr, 0x00);
   // Read address bytes
   ReadAddr(0);
   Serial.print("> Cycle power NOW to set address to: ");
   Serial.print(NewMLXAddr, HEX);
   Serial.println(" - you have 10 seconds");
   // Cycle power to MLX during this 10 second pause
   delay(10000);
   // Read temperature using default address
   ReadTemp(0);
   // Read temperature using new address (note left bit shift for reading)
   ReadTemp(NewMLXAddr<<1);
   Serial.println("**---DONE---**");
 }

 void loop(){
     delay(5000);
     ReadTemp(NewMLXAddr<<1);
 }

 word ChangeAddr(byte NewAddr1, byte NewAddr2) {
   Serial.println("> Change address");
   // Send start condition and write bit
   i2c_start_wait(0 + I2C_WRITE);
   // Send command for device to return address
   i2c_write(0x2E);
   // Send low byte zero to erase
   i2c_write(0x00);
   // Send high byte zero to erase
   i2c_write(0x00);

   if (i2c_write(0x6F) == 0) {
     // Release bus, end transaction
     i2c_stop();
     Serial.println("> Data erased.");
   }
   else {
     // Release bus, end transaction
     i2c_stop();
     Serial.println("> Failed to erase data");
     return -1;
   }

   Serial.print("> Writing data: ");
   Serial.print(NewAddr1, HEX);
   Serial.print(", ");
   Serial.println(NewAddr2, HEX);

   for (int a = 0; a != 256; a++) {
     // Send start condition and write bit
     i2c_start_wait(0 + I2C_WRITE);
     // Send command for device to return address
     i2c_write(0x2E);
     // Send low byte zero to erase
     i2c_write(NewAddr1);
     // Send high byte zero to erase
     i2c_write(NewAddr2);
     if (i2c_write(a) == 0) {
       // Release bus, end transaction then wait 10ms
       i2c_stop();
       delay(100);
       Serial.print("> Found correct CRC: 0x");
       Serial.println(a, HEX);
       return a;
     }
   }

   // Release bus, end transaction
   i2c_stop();
   Serial.println("> Correct CRC not found");
   return -1;
 }

 void ReadAddr(byte Address) {
   Serial.println("> Read address");
   // Inform the user
   Serial.print("  MLX address: ");
   Serial.print(Address, HEX);
   Serial.print(", Data: ");

   // Send start condition and write bit
   i2c_start_wait(Address + I2C_WRITE);
   // Send command for device to return address
   i2c_write(0x2E);
   i2c_rep_start(Address + I2C_READ);

   // Read 1 byte and then send ack (x2)
   Serial.print(i2c_readAck(), HEX);
   Serial.print(", ");
   Serial.print(i2c_readAck(), HEX);
   Serial.print(", ");
   Serial.println(i2c_readNak(), HEX);
   i2c_stop();
 }

 float ReadTemp(byte Address) {
   int data_low = 0;
   int data_high = 0;
   int pec = 0;

   Serial.println("> Read temperature");
   // Inform the user
   Serial.print("  MLX address: ");
   Serial.print(Address, HEX);
   Serial.print(", ");

   i2c_start_wait(Address + I2C_WRITE);
   // Address of temp bytes
   i2c_write(0x07);
   // Read - the famous repeat start
   i2c_rep_start(Address + I2C_READ);
   // Read 1 byte and then send ack (x2)
   data_low = i2c_readAck();
   data_high = i2c_readAck();
   pec = i2c_readNak();
   i2c_stop();

   // This converts high and low bytes together and processes the temperature
   // MSB is a error bit and is ignored for temperatures
   // Zero out the data
   float temp = 0x0000;
   // This masks off the error bit of the high byte, then moves it left
   // 8 bits and adds the low byte.
   temp = (float)(((data_high & 0x007F) << 8) + data_low);
   temp = (temp * 0.02) - 273.16;
   Serial.print(temp);
   Serial.println(" C");
   return temp;
 }