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HTS221是意法半导体（STMicroelectronics）生产的小体积、数字式温湿度传感器IC。该IC目前在官网仍处在“评估”状态。其主要特性：
和其他的温湿度传感器比，HTS221的芯片管脚功能更多、也略显复杂：
虽然HTS221支持I2C、3-wire SPI接口。对于3-wire SPI接口，其数据输入/输出(SDI/SDO)共用一条信号线，不同于Arduino的四线制SPI，有MOSI、MOSI信号线的区分。因此还是通过I2C接口连接。由于Arduino UNO正常工作在5V电压下，因此二者的连接还需要I2C Logic Level Converter。留意Converter带了I2C总线所需的上拉电阻。
1. HTS221内置不少寄存器，每个寄存器都有一个8bit的子地址（sub-address）。在操作时，既可以单独对某个地址的寄存器进行I2C读/写，也可以在一次I2C命令中对连续的多个地址的寄存器进行读/写。
2. 手册没有给出每次测量所需的测量时间，实测默认配置下one shot测量用时约3ms。代码中通过读取STATUS_REG寄存器，来判断一次测量是否完毕。也可以通过读取DRDY管脚信号进行判断。
3. HTS221将出厂前的校准信息保存在内部寄存器中，温度校准有两对数据：t0 & t0out, t1 & t1out，湿度校准亦有两对数据：h0 & h0t0out, h1 & h1t0out。从命名上看，湿度校准数据是在t0温度下做的。MCU将HTS221温湿度输出值得到后，还需要利用这两组校正数据进行反推（线性插值），继而获得所代表的温湿度测量结果。代码在初始化部分，读取了四组校准数据并打印了出来。
为什么不能像其他传感器那样，读出来的值就是计算好的最终结果呢？
4. Arduino库自带的map()只能对整型进行操作，因此将其改成了对浮点数进行操作。
5. 从测量结果上看，湿度动辄75%以上，明显偏高不少。
1 /* 2 Measurement of relative humidity and temperature using HTS221 3 */ 4 5 #include <Wire.h> 6 7 #define ADDRESS_HTS221 0x5F 8 #define CTRL_REG1 0x20 9 #define CTRL_REG2 0x21 10 #define STATUS_REG 0x27 11 #define HUMIDITY_OUT_L_REG 0x28 12 #define T0_degC_x8 0x32 13 #define T0_OUT 0x3C 14 #define H0_rH_x2 0x30 15 #define H0_T0_OUT 0x36 16 #define H1_T0_OUT 0x3A 17 18 byte buffer[] = {0, 0, 0, 0}; 19 byte status = 0; 20 21 float t0, t1, h0, h1; 22 int t0out, t1out, h0out, h1out; 23 24 int outHumi = 0; 25 int outTemp = 0; 26 float valueHumi = 0; 27 float valueTemp = 0; 28 29 void setup() 30 { 31 Wire.begin(); 32 Serial.begin(9600); 33 34 //turn on the HTS221, set the update mode to one shot 35 Wire.beginTransmission(ADDRESS_HTS221); 36 Wire.write(CTRL_REG1); 37 Wire.write(0x84); 38 Wire.endTransmission(); 39 40 ReadCaliData(); 41 42 //print the calibration coefficients 43 Serial.println("Calibration coefficients: "); 44 Serial.print("t0 = "); Serial.print(t0); Serial.print(" `C, t0out = "); Serial.println(t0out); 45 Serial.print("t1 = "); Serial.print(t1); Serial.print(" `C, t1out = "); Serial.println(t1out); 46 Serial.print("h0 = "); Serial.print(h0); Serial.print(" \%RH, h0out = "); Serial.println(h0out); 47 Serial.print("h1 = "); Serial.print(h1); Serial.print(" \%RH, h1out = "); Serial.println(h1out); 48 Serial.println("------------------------"); 49 } 50 51 void loop() 52 { 53 //perform a measurement 54 Wire.beginTransmission(ADDRESS_HTS221); 55 Wire.write(CTRL_REG2); 56 Wire.write(0x01); 57 Wire.endTransmission(); 58 59 //check the status 60 status = 0; 61 while (status != 0x03) //typical conversition time: 3ms 62 { 63 delayMicroseconds(3000); 64 Wire.beginTransmission(ADDRESS_HTS221); 65 Wire.write(STATUS_REG); 66 Wire.endTransmission(); 67 68 Wire.requestFrom(ADDRESS_HTS221, 1); 69 if(Wire.available() >= 1) 70 { 71 status = Wire.read(); 72 } 73 delayMicroseconds(500); 74 // Serial.println(status, HEX); 75 } 76 77 //read multiple bytes incrementing the register address 78 Wire.beginTransmission(ADDRESS_HTS221); 79 Wire.write(HUMIDITY_OUT_L_REG | 0x80); 80 Wire.endTransmission(); 81 82 Wire.requestFrom(ADDRESS_HTS221, 4); 83 if (Wire.available() >= 4) 84 { 85 for (byte i = 0; i < 4; i++) 86 { 87 buffer[i] = Wire.read(); 88 } 89 } 90 91 outHumi = (buffer[1] << 8) | buffer[0]; 92 outTemp = (buffer[3] << 8) | buffer[2]; 93 94 valueTemp = mapFloat(outTemp, t0out, t1out, t0, t1); 95 valueHumi = mapFloat(outHumi, h0out, h1out, h0, h1); 96 Serial.print(valueTemp); Serial.print(" `C, "); 97 Serial.print(valueHumi); Serial.println(" \%RH"); 98 99 delay(4000); 100 } 101 102 void ReadCaliData() 103 { 104 //read out t0degCx8, t1degCx8 105 Wire.beginTransmission(ADDRESS_HTS221); 106 Wire.write(T0_degC_x8 | 0x80); 107 Wire.endTransmission(); 108 Wire.requestFrom(ADDRESS_HTS221, 4); 109 if (Wire.available() >= 4) 110 { 111 for (byte i = 0; i < 4; i++) 112 { 113 buffer[i] = Wire.read(); 114 } 115 } 116 word t0degCx8 = ((buffer[3] & 0b00000011) << 8) | buffer[0]; 117 word t1degCx8 = ((buffer[3] & 0b00001100) << 6) | buffer[1]; 118 t0 = t0degCx8/8.0; 119 t1 = t1degCx8/8.0; 120 121 //read out t0out, t1out 122 Wire.beginTransmission(ADDRESS_HTS221); 123 Wire.write(T0_OUT | 0x80); 124 Wire.endTransmission(); 125 Wire.requestFrom(ADDRESS_HTS221, 4); 126 if (Wire.available() >= 4) 127 { 128 for (byte i = 0; i < 4; i++) 129 { 130 buffer[i] = Wire.read(); 131 } 132 } 133 t0out = (buffer[1] << 8) | buffer[0]; 134 t1out = (buffer[3] << 8) | buffer[2]; 135 136 //read out h0RHx2, h1RHx2 137 Wire.beginTransmission(ADDRESS_HTS221); 138 Wire.write(H0_rH_x2 | 0x80); 139 Wire.endTransmission(); 140 141 Wire.requestFrom(ADDRESS_HTS221, 2); 142 if (Wire.available() >= 2) 143 { 144 for (byte i = 0; i < 2; i++) 145 { 146 buffer[i] = Wire.read(); 147 } 148 } 149 byte h0RHx2 = buffer[0]; 150 byte h1RHx2 = buffer[1]; 151 h0 = h0RHx2/2.0; 152 h1 = h1RHx2/2.0; 153 154 //read out h0t0Out 155 Wire.beginTransmission(ADDRESS_HTS221); 156 Wire.write(H0_T0_OUT | 0x80); 157 Wire.endTransmission(); 158 Wire.requestFrom(ADDRESS_HTS221, 2); 159 if (Wire.available() >= 2) 160 { 161 for (byte i = 0; i < 2; i++) 162 { 163 buffer[i] = Wire.read(); 164 } 165 } 166 h0out = (buffer[1] << 8) | buffer[0]; 167 168 //read out h1t0Out 169 Wire.beginTransmission(ADDRESS_HTS221); 170 Wire.write(H1_T0_OUT | 0x80); 171 Wire.endTransmission(); 172 Wire.requestFrom(ADDRESS_HTS221, 2); 173 if (Wire.available() >= 2) 174 { 175 for (byte i = 0; i < 2; i++) 176 { 177 buffer[i] = Wire.read(); 178 } 179 } 180 h1out = (buffer[1] << 8) | buffer[0]; 181 } 182 183 float mapFloat(int x, int in_min, int in_max, float out_min, float out_max) 184 { 185 return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min; 186 }
首先打印HTS221保存的校准信息，之后会每隔4秒触发一次测量并打印结果：
与Si7021比，HTS221（under evaluation）的体积更小、接口更丰富，使用更灵活，但在硬件接口和软件操作上都略显复杂。精度上，datasheet也并未给出已验证的典型误差和最大误差，实测湿度误差较大。
HTS221 Capacitive digital sensor for relative humidity and temperature
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原文地址：http://www.cnblogs.com/zlbg/p/4216251.html
