#include <Wire.h>

#define I2C_SLAVE_ADDRESS 0x4 // the 7-bit address

#define MEASURE_TEMPERATURE     0xA0
#define SEND_TEMPERATURE        0xB0

#define TEMP_CONST  10  // (1 Celcius == 10 mV)
#define TEMP_RESOLUTION  1024 // 2^10 (10 bits)
#define UNIT_CHANGE  1000  // (1V = 1000 mV)
#if defined(ARDUINO_ARCH_ESP8266) || defined(__CC3200R1M1RGC__)
#define SUPPLY_VOLTAGE  3.3 // VCC votage for ESP8266
#else
#define SUPPLY_VOLTAGE  5.0 // VCC votage for ATmega328p
#endif


float temp;
const float temp_magic_no = (((SUPPLY_VOLTAGE * UNIT_CHANGE) / TEMP_RESOLUTION) / TEMP_CONST);
int temperature;
volatile uint8_t buffer[2];


void setup()
{
    Wire.begin(); // join i2c bus (address optional for master)
    Serial.begin(115200);
    Serial.println("START...");
}


void loop()
{
    Wire.beginTransmission(I2C_SLAVE_ADDRESS); // transmit to device #4
    Wire.write(MEASURE_TEMPERATURE);        // sends five bytes
    Wire.endTransmission();    // stop transmitting
    delay(100);

    Wire.beginTransmission(I2C_SLAVE_ADDRESS); // transmit to device #4
    Wire.write(SEND_TEMPERATURE);
    Wire.endTransmission();
    Wire.requestFrom(I2C_SLAVE_ADDRESS, 2);
    buffer[0] = Wire.read();
    buffer[1] = Wire.read();
    temperature = (buffer[0] << 8) | buffer[1];

    Serial.print("raw adc value = ");
    Serial.println(temperature);

    temp = temperature * temp_magic_no;
    Serial.print("current temperature = ");
    Serial.println(temp);

    delay(2000);
}