Integrated temperature and humidity sensors of small size and high accuracy are widely applied in cellphones, communication, HVAC, medical care, environment monitoring, home appliances and control panels. Here we ISWeek would like to compare the two best sellers in the market – HTU21D and SHT21- from aspects of their cost efficiency, performance and power consumption for your reference.
1. Features of HTU21D
Based on high-performance humidity sensing elements, the new humidity and temperature sensor of MEAS is about to set new standards in terms of size and intelligence: Embedded in a reflow solderable Dual Flat No leads (DFN) package of 3 x 3mm footprint and 1mm height it provides calibrated, linear signals in digital, I2C format.
The cutting-edge digital temperature and humidity sensor HTU21D has established a new model for its size and intelligence: DFN package, with its size of 3 x 3 x 1mm; providing factory-calibrated, linear I²C digital output signals.
HTU21D is a plug-and-play compound sensor measuring temperature and humidity, which is an ideal choice for OEM applications demanding reliable and accurate measurement. Digital output of temperature and humidity signals directly interface to micro controllers. Each of the sensors is calibrated and tested, with their batch number printed on the casing and stored in the memory chips, which can be easily read by command. Users can change HTU21D’s resolution （from 8/12bit to 12/14bit）by command.
Besides, the sensors can be used in the detection of low battery, validation and improving reliability of communication. With its low power consumption, high cost efficiency and compact size, HTU21D is suitable for OEM applications in large volume, which is sensitive in price and limited in mounting space, such as motors, vehicles, medical care, industrial control, consumer electronics and home appliances.
2. Comparison of major parameters
It can be seen from the chart above that:
Though sharing similar specs, HTU21D enjoys some advantages over SHT21: wider power supply range （1.5V—3.6V）, lower power consumption（2.7uW）, higher accuracy on humidity than SHT20（±3.5%RH）, and equal to SHT21（±2%RH）, lower price and shorter response time within 5S.
3. HTU21D’s dimensions
Note: All dimensions are in mm, with a tolerance of ±0.1mm. The sensor has been through ground processing.
- back view and dimensions of the sensor
4. Comparison of appearance between HTU21D and SHT21
See them from the dimensions and distribution and definition of pins, HTU21D and SHT21 are completely the same, so they can replace each other pin to pin just like the picture below.
5. Comparison of software of HTU21D and SHT21
Both HTU21D and SHT21 adopt I2Cinterface digital output and have the same start-up and stop signal timing sequence.
- Start up signal
Start transferring. A single data bit includes a jump on DATA lime from the SCK line high to low.
- stop signal
Stop transferring. When a jump on DATA lime from SCK line high to low.
When the transfer is terminated and data transmission is stopped, the SC line with the DATA line jumps from low to high.
HTU21D and SHT21 share the same command list.
Therefore, on the aspect of software and protocol, HTU21D and SHT20, SHT21 are entirely compatible and replaceable with each other.
Conclusion
HTU21D is perfectly compatible with SHT20 and SHT21. They can be replaced Pin to Pin on hardware, with no need for board modifications; on software, they are the same and completely replaceable. See it from the manufacturer’s quotations, the price of HTU21D is better than SHT20 and SHT21 for uses to lower their production cost.
