Product Introduction
The new generation HTU21D temperature and humidity sensor has established new standards in terms of size and intelligence: it is embedded in a double row flat no pin DFN package suitable for reflow soldering, with a bottom surface of 3x3mm and a height of 1.1mm. The sensor outputs a calibrated digital signal in standard I2C format. The HTU21D temperature and humidity sensor provides accurate and reliable temperature and humidity measurement data for 0EM applications. Temperature and humidity digital outputs are achieved through the interface and module connection of a microcontroller. The resolution of HTU21D can be changed by inputting commands (8/12 bit or even 12/14 bit RH/T), and the sensor can detect low battery status and output a checksum, which helps improve communication reliability.
Device Characteristics
| 参数 Parameters | 符号 Symbol | 参数值 Parameter values | 单位 Company |
| 储藏温度 Storage temperature | Tstg | -40 to +125 | ℃ |
| 供电电压(峰值) Supply voltage (peak value) | Vcc | 3.8 | Vdc |
| 湿度测量范围 Humidity measurement range | RH | 0 to 100 | %RH |
| 温度测量范围 Temperature measurement range | Ta | -40 to +105 | ℃ |
| VDD to GND | -0.3 to 3.6V | Vdc | |
| 数字I/0口引脚(DATA/SCK)to VDD Digital I/O port pin (DATA/SCK) to VDD | -0.3 to VDD+0.3 | Vdc | |
| 每个引脚输入电流 Input current for each pin | -10 to +10 | mA |
(At T=25 ℃, Vd=3.3V)
| 特性 Characteristic | 符号 Symbol | 最小值 Minimum value | 典型值 Typical values | 最大值 Maximum value | 单位 Company | |
| 分辨率 Resolving power | 12位 | 0.04 | %RH | |||
| 8位 | 0.7 | %RH | ||||
| 湿度测量范围 Humidity measurement range | RH | 0 | 100 | %RH | ||
| 湿度测量精度(10%-95%RH) Humidity measurement accuracy (10% -95% RH) | 典型值 Typical values | ±2 | %RH | |||
| 最大值 Maximum value | ±3 | ±5 | ||||
| 湿度磁滞 Humidity hysteresis | ±1 | %RH | ||||
| 测量时间 Measurement time | 12位 | 14 | 18 | ms | ||
| 11位 | 7 | 9 | ms | |||
| 10位 | 4 | 5 | ms | |||
| 8位 | 2 | 3 | ms | |||
| 结露150小时后的恢复时间 Recovery time after 150 hours of condensation | t | 10 | s | |||
| 长期漂移 Long term drift | 0.5 | %RH/yr | ||||
| 响应时间 Response time | TRH | 5 | 10 | s |
Product Description
| 引脚 Pin | 说明 Explain |
| 电源引脚 (VDD.GND) | HTU21 的供电范围为 1.8VDC.3.6VDC，推荐电压为3.0V。电源(VDD)和接地(VSS)之间须连接一个0.1uF的去耦电容，且电容的位置应尽可能靠近传感器。 The power supply range of HTU21 is 1.8VDC.3.6VDC, and the recommended voltage is 3.0V. A 0.1uF decoupling capacitor must be connected between the power supply (VDD) and ground (VSS), and the capacitor should be located as close as possible to the sensor. |
| 串行时钟输入 (SCK) | SCK 用于微处理器与 HTU21 之间的通讯同步。由于接口包含了完全静态逻辑，因而不存在最小SCK 频率。 SCK is used for communication synchronization between microprocessors and HTU21. Due to the interface containing completely static logic, there is no minimum SCK frequency. |
| 串行数据 (DATA) | DATA 引脚为三态结构，用于读取传感器数据。当向传感器发送命令时,DATA 在 SCK 上升沿有效目在 SCK 高电平时必须保持稳定。 DATA 在 SCK 下降沿之后改变。当从传感器读取数据时, DATA 在SCK 变低以后有效，且维持到下一个 SCK的下降沿。为避免信号冲突，微处理器应驱动 DATA 在低电平。需要一个外部的上拉电阻(例如: 10k9)将信号提拉至高电平。上拉电阳通常已包含在微处理器的 I/0 电路中。 The DATA pin is a three state structure used to read sensor data. When sending commands to sensors, DATA must remain stable at the SCK high level when the effective target is on the rising edge of SCK. DATA changes after the falling edge of SCK. When reading data from sensors, DATA becomes effective after SCK decreases and remains valid until the falling edge of the next SCK. To avoid signal conflicts, the microprocessor should drive DATA at a low level. We need an external pull-up resistor (e.g.: Lift the signal to a high level (10k9). The pull-up battery is usually included in the I/O circuit of the microprocessor. |
Design Description
If the SCL and SDA signal lines are parallel and very close to each other, it may cause signal crosstalk and communication failure. The solution is to place VDD or GND between two signal lines to separate them, or use shielded cables. In addition, reducing the SCL frequency may also improve the integrity of signal transmission. A 100nF decoupling capacitor must be added between the power pins (VDD, GND) for filtering. This capacitor should be placed as close as possible to the sensor.
Data fetch
The default resolution set inside the sensor is 12 bits for relative humidity and 14 bits for temperature. The output data of SDA is converted into a two byte packet, with the high byte MSB placed first (left aligned). Each byte is followed by a response bit. The two status bits, namely the last two bits of LSB, must be set to '0' before performing physical calculations.
The HTU21D is a low-cost, easy to use, highly accurate, digital humidity and temperature sensor. This sensor is ideal for environmental sensing and data logging and perfect for a weather stationsor humidor control systems. All you need is two lines for l2C communication and you'll have relative humidity readings and veryaccurate temperature readings as a bonus!
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