There is no need to wait for something after a Wire.requestFrom().
When the Wire.requestFrom() returns, I2C bus transaction has completely finished and the received data is waiting in a buffer in the Wire library.

These pieces of code can be removed:

//Wait for data to become available
int counter = 0;
while(!Wire.available()){
  counter++;
  delay(1);
  if(counter > 100) return HTU21D_I2C_TIMEOUT; //after 100ms consider I2C timeout
}

If you want, then it is possible to test if the Wire.requestFrom() was succesful or not:

Wire.requestFrom(HTDU21D_ADDRESS, 3);

//Test if something was wrong
if(Wire.available() != 3){
  return HTU21D_I2C_TIMEOUT;
}

uint16_t h = Wire.read();
h <<= 8;
h |= Wire.read();

You could replace the "TIMEOUT" error with a more appropriate name. When it failed, the Slave was not answering or there was a bus error.

Hi @romainmp.

I'm trying to get the code running with the adafruit HTU21DF and your library but it's not working. I just create the htu object and then see !htu.begin()

The LED in the front of the photon doesn't breathe cyan anymore (It's fixed) It's like the micro isn't responding. Do you know anything about this?

Thanks!

Veryfing code using this library in Particle Build fails with this error:

HTU21D/HTU21D.h:39:7: error: redefinition of 'class HTU21D'
 class HTU21D {
       ^