Wiring & Test

You can easily wire this breakout to any microcontroller, we'll be using an Arduino. For another kind of microcontroller, just make sure it has I2C, then port the code - its pretty simple stuff!
  • Connect Vin to the power supply, 3-5V is fine. Use the same voltage that the microcontroller logic is based off of. For most Arduinos, that is 5V
  • Connect GND to common power/data ground
  • Connect the SCL pin to the I2C clock SCL pin on your Arduino. On an UNO & '328 based Arduino, this is also known as A5, on a Mega it is also known as digital 21 and on a Leonardo/Micro, digital 3
  • Connect the SDA pin to the I2C data SDA pin on your Arduino. On an UNO & '328 based Arduino, this is also known as A4, on a Mega it is also known as digital 20 and on a Leonardo/Micro, digital 2
The HTU21D-F has a default I2C address of 0x40 and cannot be changed!

Download Adafruit_HTU21DF

To begin reading sensor data, you will need to download Adafruit_HTU21DF_Library from our github repository. You can do that by visiting the github repo and manually downloading or, easier, just click this button to download the zip
Rename the uncompressed folder Adafruit_HTU21DF and check that the Adafruit_HTU21DF folder contains Adafruit_HTU21DF.cpp and Adafruit_HTU21DF.h

Place the Adafruit_HTU21DF library folder your arduinosketchfolder/libraries/ folder.
You may need to create the libraries subfolder if its your first library. Restart the IDE.

We also have a great tutorial on Arduino library installation at:
http://learn.adafruit.com/adafruit-all-about-arduino-libraries-install-use

Load Demo

Open up File->Examples->Adafruit_HTU21DF->HTU21DFtest and upload to your Arduino wired up to the sensor
Thats it! Now open up the serial terminal window at 9600 speed to begin the test.
You can try breathing on the sensor to increase the humidity. The sensor reacts very fast!

Library Reference

The library we have is simple and easy to use

You can create the Adafruit_HTU21DF object with:
Adafruit_HTU21DF htu = Adafruit_HTU21DF()
There are no pins to set since you must use the I2C bus!

Then initialize the sensor with:
htu.begin()
this function returns True if the sensor was found and responded correctly and False if it was not found

Once initialized, you can query the temperature in °C with
htu.readTemperature()
Which will return floating point (decimal + fractional) temperature. You can convert to Fahrenheit by multiplying by 1.8 and adding 32 as you have learned in grade school!

Reading the humidity is equally simple. Call
htu.readHumidity()
to read the humidity also as a floating point value between 0 and 100 (this reads % humidity)
This guide was first published on Jun 03, 2014. It was last updated on Jun 03, 2014. This page (Wiring & Test) was last updated on May 04, 2015.