Integrated temp&humidity sensors of small size and high accuracy are widely applied in cellphones, communication, HVAC, medical care, environment monitoring, home appliance and control panels. Here we ISWeek would like to make a comparison between the two best sellers in the market – HTU21D and SHT21- from aspects of their cost efficiency, performance and power consumption for your reference.
HTU21D
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 foot print and 1mm height it provides calibrated, linear signals in digital, I2C format.
The cutting edge digital temp&humidity sensor HTU21D has established a new model for its size and intelligence: DFN packaged, 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 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 application 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:
| Model | HTU21D | SHT21 |
| Supply voltage | 1.5V—3.6 | 2.1V—3.6V |
| Humidity range | 0—100%RH | 0—100%RH |
| Temperature range | -40℃—105℃ | -40℃—105℃ |
| Max consumption power | 2.7uW | 3.2uW |
| Communication method | I2C | I2C |
| Humidity accuracy range(10% to 95%) | HTU21D ±2%RH | SHT21 ±2%RH |
| Humidity delay | ±1%RH | ±1%RH |
| Measurement time | 50ms | 50ms |
| Annual offset | -0.5%RH/year | -0.5%RH/year |
| Response time | 5s | 8s |
It can be seen from the chart above that:
Though sharing the 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.
- HTU21D’s dimensions are as follows:
1) Dimensions:
Note: all dimensions are in mm, with the tolerance of ±0.1mm. The sensor has been through ground processing.
- back view and dimensions of the sensor
HTU21D’s footprint in mm
- 4. Comparison of appearance between HTU21Dand SHT21
See them from dimensions and distribution and definition of pins, HTU21D and SHT21 are completely the same, so that they can replace each other pin to pin just like the picture below.
5. Comparison on software of HTU21D & SHT21
Both HTU21D and SHT21 adopt I2Cinterface digital output, as well as 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 SCK line high to low.
- stop signal
Stop transferring. When a jump on DATA lime from SCK line high to low.
When transfer is terminated and data transmission is stopped, SC line with DATA line jump 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.
6. Actual measurement performance of temperature and humidity sensor HTU21D :
1）Here is the data logs of quaternity temperature&humidity demo tests implemented by ISWeek:
Four in one demo of temp&humidity display
It can be seen from the pics above that the 4pcs of HTU21D are of excellent consistency and reliability.
2）Data comparison between high accuracy HHU and HTU21 with HTU21 1602LCD display:
For the convenience of tests, the manufacturer provides HTU21PCBA with small PCB:
The comparison between high accuracy HHU and the combination of HTU21PCBA with board and 1602LCD for display:
Conclusion: HTU21D is perfectly compatible with SHT20 and SHT21. On hardware they can be replaced Pin to Pin, with no need of board modifications; on software they are basically 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.
