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Description: The HTU21D is a low-cost, easy to use, highly accurate, digital humidity and temperature sensor. This sensor is ideal for environmental sensing and data logging and perfect for a weather stations or humidor control systems. All you need is two lines for I2C communication and you’ll have relative humidity readings and very accurate temperature readings as a bonus!

There are only four pins that need to be hooked up in order to start using this sensor in a project. One for VCC, one for GND, and two data lines for I2C communication. This breakout board has built in 4.7k pull up resistors for I2C communications. If you’re hooking up multiple I2C devices on the same bus, you may want to disable these resistors.

Dimensions: 0.6 x 0.6"


Comments 31 comments

  • Heads up, this is not 5V tolerant. Absolute maximum is 3.8V

  • The pullup resistor enable/disable solder blob is an amazing idea and should be included on all i2c breakouts!

  • Is this sensor suitable for outdoor monitoring? I can shield it from the rain, but dew is a concern for many sensors. Thanks.

  • I managed to get this working with a BeagleBone Black? I’ve left the pull-up resistors intact even though I’ve read the BeagleBone Black has internal pull-ups (not sure). But I’m getting very inaccurate temperature readings (about 10-12F above real temperature). Can’t verify humidity.

  • Vid 1 - Humidity and 4D Systems uOLED-128-G2

    Vid 2 - Temp and 4D Systems uOLED-128-G2

    I’m very happy with the product, im currently experimenting with this Breakout and the 4D Systems uOLED-128-G2 screen.

  • I couldn’t get this to work with UNO (5v) using the 10k resistors (998 errors). I had to use a level converter.

    • Really? I did all my testing with a 5V Uno. Did you use the configuration in the hookup guide? Could you double check they are indeed 10ks?

      • Same thing here with the example code listed above. Using 10K resistors (double checked) and followed hookup guide to the T. Get the 998 error.

        • Got rid of the 10K resistors per tech support and it works great. Temp was accurate to .3 degrees when compared to a laboratory grade thermometer. Humidity seems to be right on although I don’t have anything to compare it to. Great product for the price.

          • Shoot! Sorry about that. I was able to replicate your error. Using 330 ohm resistors works well for me. I’ll update the assembly guide.

          • Same issue. I tried 2 different RedBoards with the 10 Ks. Only got the 998 error. Removed the inline resistors and it worked great. Should I be worried about running it without the resistors?

  • Anyone happen to access this sensor via python (maybe on a raspberry pi)? I’m attempting that and having a devil of a time getting readings. Code examples would be appreciated

  • How do I address multiple sensors on the same I2C bus? They are all using 0x40 for I2C address, and I saw no documentation to change the address.

    • The HTU21D doesn’t have the ability to change its address. You would need to power down units that you don’t want to talk to or perhaps use a software I2C library to have multiple sensors hooked up to different pins.

  • Making me nervous…No production plans?

    • We’ll be building plenty once the parts arrive. The automated system is not the greatest when some info is not available.

  • What are the actual dimensions for this board?.

    • 0.6 x 0.6" square. I’ll add to the description. Lemme know if you need any other dimension.

  • Do these have the same re-hydration requirements as the honeywell and the like?

    • Yes, but we re-hydrate/re-calibrate them in house so you don’t have to worry about it.

  • Looks like a cheaper knock-off of the Sensirion SHT21. I2C address and register addresses are the same, so you should be able to use existing code then…

    • Hold the PHONE !!! Does that mean that the problems with the SHT21 not being fully i2C compatible apply to this one too?

      • As far as I can tell the HTU21D is fully I2C compliant. I ran into no problems using it along side multiple other devices on the bus.

    • I was going to call you crazy, but you’re right. It’s shockingly similar. Same pinout, same footprint. I wouldn’t say anyone is knocking anyone else off, but I’m certainly not sure who is licensing what technology from who. Either way, the HTU21D is way cheaper, we’re super impressed with it, and we’ve got a library that works really well with it.

  • Does the HTU21D also need to be shielded from direct light exposure like the HIH-4030 for better accuracy?

    • That’s a really interesting question. A quick google search pointed me at a datasheet from April 2012 (older than the one we host). And according to it “HTU21D sensors are not light sensitive.” This is not in the current datasheet so I’m not sure. Perhaps someone at Measure Specialties knows.

  • Well, this is damn near perfect. Accurate digital humidity at 3.3v (most are analog, and many are 5V) and very accurate temperature. Exactly what I have been waiting for!

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