SHT11 is a single-chip fully calibrated digital relative humidity and temperature sensor with I2C bus interface produced by the Swiss company Sensirion. This sensor uses unique CMOSens TM technology and has the characteristics of digital output, no need for debugging, no need for calibration, no need for peripheral circuits and full interchangeability. This article elaborates on the performance characteristics, interface timing and commands of the sensor, and provides the interface circuit between SHT11 and the microcontroller and the corresponding program. Keywords: digital; temperature and humidity sensor; I2C bus; microcontroller 1 Overview Temperature and humidity measurement is widely used in warehousing management, production and manufacturing, meteorological observation, scientific research and daily life. Traditional analog humidity sensors generally need to be designed Signal conditioning circuits also need to go through complex calibration and calibration processes, so measurement accuracy is difficult to guarantee, and linearity, repeatability, interchangeability, consistency, etc. are often unsatisfactory. SHT11 is a new temperature and humidity sensor based on CMOSensTM technology launched by the Swiss company Sensirion. This sensor combines CMOS chip technology and sensor technology to bring into play their powerful complementary advantages.
2 Performance Features The main features of the SHT11 temperature and humidity sensor are as follows: ●The temperature and humidity sensor, signal amplification and conditioning, A/D conversion, and I2C bus interface are all integrated into one chip (CMOSensTM technology); Fully calibrated relative humidity and temperature value output; ●With industry-standard I2C bus digital output interface; ●With dew point value calculation output function; ●Excellent long-term stability; ●Humidity value output resolution is 14 bits, temperature value The output resolution is 12 bits and can be programmed to 12 bits and 8 bits; ●Small size (7.65×5.08×23.5mm), can be surface mounted; ●Has reliable CRC data transmission verification function; ●The calibration coefficient loaded on the chip can ensure 100% interchangeability; ●The power supply voltage range is 2.4 ~ 5.5V; ●The current consumption is 550μA when measured, the average is 28μA, and 3μA when sleeping.
The SHT11 temperature and humidity sensor adopts SMD (LCC) surface mount package. The pin arrangement is shown in Figure 1. The pin description is as follows: (1) GND: ground terminal; (2) DATA: Bidirectional serial data line; (3) SCK: serial clock input; (4) VDD power supply terminal: 0.4~5.5V power supply terminal; (5~8) NC: empty pin.
3 Working Principle The humidity detection of SHT11 uses a capacitive structure, and uses a "microstructure" detection electrode system with different protections and a polymer covering layer to form the capacitance of the sensor chip. In addition to maintaining the capacitive humidity sensor In addition to the original characteristics of the device, it can also resist influences from the outside world. Because it combines the temperature sensor and the humidity sensor to form a single entity, the measurement accuracy is high and the dew point can be accurately obtained without errors caused by changes in the temperature gradient between the temperature and humidity sensors. CMOSensTM technology not only combines temperature and humidity sensors, but also integrates signal amplifier, analog/digital converter, calibration data memory, standard I2C bus and other circuits into one chip. The internal structure block diagram of the SHT11 sensor is shown in Figure 2. Each SHT11 sensor is calibrated in an extremely precise humidity chamber. The calibration coefficients of the SHT11 sensor are pre-stored in the OTP memory. The calibrated relative humidity and temperature sensor is connected to a 14-bit A/D converter, which can send the converted digital temperature and humidity values ??to the second-line I2C bus device, thereby converting the digital signal into a serial number that complies with the I2C bus protocol. Signal