HTU21D / Si72021 Temperature and Humidity Sensor
I have been been evaluating the HTU21D temperature and humidity sensor made by Measurement Specialties as a possible DHT22 replacement for the emonTH. This is quite a new sensor, released in 2013. The Si72021 is also a posiblity with an identical pin-out and specs.
- OctoPart list
- Datasheet
- Farnell item
- DFM footprint
- Digital, pre-clibrated
- I2C
The metrics speak for themselves:
| Metric | HTU21D | Si72021 | DHT22 | DHT22 vs HTU21D Difference |
|---|---|---|---|---|
| Cost in 1k off | £1.42 (July16) | £2.15 | £4.57 (July16) | 3.2 times cheaper (£3.15 less!) |
| Vcc | 2.1v - 3.6V | 1.9V - 3.6V | 3.3-6V | |
| Humidity accuracy | ±2% RH | ±2% RH | ±2%RH | n/a |
| Humidity Range | 0-100% RH | 0-100% RH | 0-100% RH | n/a |
| Temperature accuracy | ±0.3°C | ±0.4°C | ±0.5°C | 40% more accurate |
| Temperature Range | -40°C +125°C | -40°C +125°C | -40°C +80°C | 56% more accurate |
| Sleep Current | 0.02uA | 0.06uA | 15uA | 750 times less power |
| Measurement Current | 0.045mA | 0.09 mA | 0.5mA | 11 times less power |
| Measurement time | 0.01s - 0.0026s | 0.01s - 0.0026s | 2s | 200 times faster |
| Energy consumed per sample | 0.00045mW | 1mW | 2222 times less power | |
| Time sampling per day* | 14.4s | 2800s | ||
| Time sleeping per day* | 86386s | 83600s | ||
| Energy consumed per day* | 2.36mW [1] | 2836mW [2] | 1201 times less energy per day! |
*Assuming 1 sample per min and sleeping in between samples, 1440 min per day = 86400s per day. See HTU21D testing repo a sub-repository of the emonTH for full calculations.
An upgraded emonTH with a HTU21D sensor instead of DHT22 should benefit from substantially increased battery life, increased accuracy and lower cost.
I’ve obtained HTU21D Sparkfun breakout to test and easily got it working with an Arduino using the Adafruit library.
There is some confusion with regard to the variants of this sensor I believe from my research that the HTU21D replaces the SHT21 made by Sensirion. Both sensors have identical pin-outs.
I hope to get a prototype emonTH with HTU21D up and running soon. I would be interested to hear if anyone has experience working with this sensor.
For disucssion see HTU21D forum thread.
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