Performance evaluation of ultra small volume temperature and humidity sensors HTU21D and SHT21

Performance evaluation of ultra small volume temperature and humidity sensors HTU21D and SHT21
Ultra small size of the temperature and humidity sensor with small volume, high accuracy, is widely used in mobile phone, HVAC, communications, medical, environmental monitoring, household appliances, control panels, editor recently from isweek ( http://www.isweek.com/ ) to get the market on the most commonly used HTU21 and SHT21 two of the sample product. These two kinds of products to do a detailed comparative evaluation, the evaluation focuses on the price, performance, power consumption and other aspects of analysis, for your reference.

HTU21d
1、HTU21D temperature and humidity sensor features
Humidity sensing elements made of high performance based on a new generation of HTU21D temperature and humidity sensors set new standards in size and intelligence: it embeds without pin DFN package for double row flat reflow, bottom 3x3mm, 1.1mm. height sensor output after calibration of the digital signal, the standard I2C format. The output mode of diversification the wide operating voltage range, with high accuracy and precision of temperature humidity.HTU21 series module designed for low-power small volume design, good quality, fast response speed, strong anti-interference ability, high price Dots, tiny volume (3x3mm), and extremely low power dissipation make the HTU21D the choice for all types of applications.
2、Comparison of important parameters of HTU21 and SHT21 sensors：

Module	HTU21D	SHT21
Supply Voltage	1.5-3.6V	2.1-3.6V
Humidity operating range	0-100%RH	0-100%RH
Tempertaure operating range	-40℃-125℃	-40℃-125℃
Maximum power consumption	2.7uW	3.2uW
Output	I2C	I2C
Relative Humidity Accuracy	±2%RH	±2%RH
Response Time	5S	8S

From the above comparison can be seen:
Although the HTU21D and SHT21 parameters are generally similar, but slightly HTU21D some advantages: wide supply voltage (1.5V - 3.6V), lower power consumption than the SHT21 (2.7uW), HTU21D + 2%RH with humidity accuracy is higher than SHT20 (+ 3.5%RH), equivalent to SHT21 (+ 2%RH), but the price is over SHT21 cheaper, 5S response time is faster.
3. HTU21D sensor size is as follows:
1) Sensor size：

Note: dimensions are mm, tolerance is + 0.1mm, has grounding sensor at the bottom.
2） The back electrode of the sensor and size

4、Comparison of appearance and pin aspects of HTU21D and SHT21
The appearance and size distribution and pin definition, HTU21D and SHT21 are exactly the same, can be directly implemented pin to pin replacement.
 
HTU21D                       SHT21
　　5、HTU21D and SHT21 software：
The HTU21D and SHT21 are both I2C interface digital outputs with the same timing of start and stop signals.
· Activating signal
Start the transmission, sending a data, including the DATA line in the SCK line during a high level to low level jump.

· Break alarm
The termination of transmission, stop sending data, including the DATA line in the SCK line of high level during a jump to a high level.

HTU21D and SHT21 have the same command list：
 
Both HTU21D and SHT21 are the actual use of the four pins, power supply and power supply, two port I2C communication. The output is digital quantity: 14 bit and 12 bit temperature humidity value, can also through the user registers to modify 12 temperature and 8 humidity.
Therefore, HTU21D and SHT20, fully compatible with SHT21 protocol software, can be replaced by each other.
6、HTU21D temperature and humidity sensor actual measurement effect display:
1）Using four bit temperature and humidity demonstration Demo test, and with the host computer software to implement data records:

Four bit temperature and humidity demonstrationDemo

PC recording software
As can be seen from the figure above, the consistency of the 4 HTU21D products is very good. From the graph, we can see that the recorded data curve has been flat, indicating that the HTU21D stability is good
2）Using homemade ribbon HTU21 with 1602LCD display, and high-precision handheld table data contrast
In order to facilitate customer testing, manufacturers introduced has been welded with small PCB board HTU21D PCBA:


Conclusion: HTU21D and SHT20, fully compatible with SHT21, hardware pins can achieve Pin to Pin, no need to modify the circuit board. The software program is basically the same, both can achieve a compatible replacement, do not need to make any changes. From the manufacturer's price, HTU21D SHT21 more than SHT20, the price advantage is good choice for manufacturers to reduce production cost.