const byte REG_ADDR_RESULT = 0x00;
  const byte REG_ADDR_CONFIG = 0x02;

  // initialize the Wire library
  Wire.begin();
  Wire.setClock(400000);

  // configure the ADC
  Wire.beginTransmission(I2C_ADC121);
  Wire.write(REG_ADDR_CONFIG);
  Wire.write(REG_ADDR_RESULT);
  Wire.endTransmission();

  // set the 'result' register as default
  Wire.beginTransmission(I2C_ADC121);
  Wire.write(REG_ADDR_RESULT);
  Wire.endTransmission();

unsigned short adcRead() {
  Wire.requestFrom(I2C_ADC121, 2); // request 2 bytes
  byte buff[2];
  Wire.readBytes(buff, 2); // read2 bytes
  return (buff[0] << 8) | buff[1]; // get the result as 16 bit number
}