rduino I2C + 温湿度传感器HTS221#
https://www.cnblogs.com/zlbg/p/4216251.html
主要特性#
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:
工作电压:1.7~3.6V
数据输出频率(ODR)可设:1Hz ~ 12.5Hz
低功耗:2μA@1Hz ODR
温度精度:给出误差典型值+/-0.5°C, 15~40°C;但注明“Typical specifications are not guaranteed.”。无误差最大值信息。
湿度精度:给出误差典型值+/-4.5%RH, 20~80%RH;同样注明“Typical specifications are not guaranteed.”。无误差最大值信息。
内置16-bit ADC
接口:I2C或3-wire SPI
出厂已校准,但需要用户自行读取校准信息、并计算校准后的结果
封装:2 x 2 x 0.9mm HLGA-6L封装,是已知同类传感器中体积最小的
片上集成加热器(heater)
管脚定义#
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:
VDD:电源,支持1.7~3.6V电压
GND:地
CS:I2C/3-wire SPI接口选择,当CS=1时为I2C接口,反之为3-wire SPI接口。默认为1。
SCL/SPC:I2C或3-wire SPI接口的时钟线,由CS选择。
SDA/SDI/SDO:I2C或3-wire SPI接口的数据线,由CS选择。
DRDY:提供Data Ready信号输出。当测量完成、有温湿度数据可供读取时,DRDY为高电平;当无温湿度数据、或温湿度数据已被读取完毕后,DRDY为低电平。该功能也可以通过设置控制寄存器(CTRL_REG3)关闭。
与Arduino的连接#
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。
功能调试#
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。
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。
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?
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。
从测量结果上看,湿度动辄75%以上,明显偏高不少。
尝试用中断函数捕获DRDY上升沿,进而在中断函数中进行数据读取。可是不知为何,中断函数会卡在对I2C的操作上。
测试代码#
/*
Measurement of relative humidity and temperature using HTS221
*/
#include <Wire.h>
#define ADDRESS_HTS221 0x5F
#define CTRL_REG1 0x20
#define CTRL_REG2 0x21
#define STATUS_REG 0x27
#define HUMIDITY_OUT_L_REG 0x28
#define T0_degC_x8 0x32
#define T0_OUT 0x3C
#define H0_rH_x2 0x30
#define H0_T0_OUT 0x36
#define H1_T0_OUT 0x3A
byte buffer[] = {0, 0, 0, 0};
byte status = 0;
float t0, t1, h0, h1;
int t0out, t1out, h0out, h1out;
int outHumi = 0;
int outTemp = 0;
float valueHumi = 0;
float valueTemp = 0;
void setup()
{
Wire.begin();
Serial.begin(9600);
//turn on the HTS221, set the update mode to one shot
Wire.beginTransmission(ADDRESS_HTS221);
Wire.write(CTRL_REG1);
Wire.write(0x84);
Wire.endTransmission();
ReadCaliData();
//print the calibration coefficients
Serial.println("Calibration coefficients: ");
Serial.print("t0 = "); Serial.print(t0); Serial.print(" `C, t0out = "); Serial.println(t0out);
Serial.print("t1 = "); Serial.print(t1); Serial.print(" `C, t1out = "); Serial.println(t1out);
Serial.print("h0 = "); Serial.print(h0); Serial.print(" \%RH, h0out = "); Serial.println(h0out);
Serial.print("h1 = "); Serial.print(h1); Serial.print(" \%RH, h1out = "); Serial.println(h1out);
Serial.println("------------------------");
}
void loop()
{
//perform a measurement
Wire.beginTransmission(ADDRESS_HTS221);
Wire.write(CTRL_REG2);
Wire.write(0x01);
Wire.endTransmission();
//check the status
status = 0;
while (status != 0x03) //typical conversition time: 3ms
{
delayMicroseconds(3000);
Wire.beginTransmission(ADDRESS_HTS221);
Wire.write(STATUS_REG);
Wire.endTransmission();
Wire.requestFrom(ADDRESS_HTS221, 1);
if(Wire.available() >= 1)
{
status = Wire.read();
}
delayMicroseconds(500);
// Serial.println(status, HEX);
}
//read multiple bytes incrementing the register address
Wire.beginTransmission(ADDRESS_HTS221);
Wire.write(HUMIDITY_OUT_L_REG | 0x80);
Wire.endTransmission();
Wire.requestFrom(ADDRESS_HTS221, 4);
if (Wire.available() >= 4)
{
for (byte i = 0; i < 4; i++)
{
buffer[i] = Wire.read();
}
}
outHumi = (buffer[1] << 8) | buffer[0];
outTemp = (buffer[3] << 8) | buffer[2];
valueTemp = mapFloat(outTemp, t0out, t1out, t0, t1);
valueHumi = mapFloat(outHumi, h0out, h1out, h0, h1);
Serial.print(valueTemp); Serial.print(" `C, ");
Serial.print(valueHumi); Serial.println(" \%RH");
delay(4000);
}
void ReadCaliData()
{
//read out t0degCx8, t1degCx8
Wire.beginTransmission(ADDRESS_HTS221);
Wire.write(T0_degC_x8 | 0x80);
Wire.endTransmission();
Wire.requestFrom(ADDRESS_HTS221, 4);
if (Wire.available() >= 4)
{
for (byte i = 0; i < 4; i++)
{
buffer[i] = Wire.read();
}
}
word t0degCx8 = ((buffer[3] & 0b00000011) << 8) | buffer[0];
word t1degCx8 = ((buffer[3] & 0b00001100) << 6) | buffer[1];
t0 = t0degCx8/8.0;
t1 = t1degCx8/8.0;
//read out t0out, t1out
Wire.beginTransmission(ADDRESS_HTS221);
Wire.write(T0_OUT | 0x80);
Wire.endTransmission();
Wire.requestFrom(ADDRESS_HTS221, 4);
if (Wire.available() >= 4)
{
for (byte i = 0; i < 4; i++)
{
buffer[i] = Wire.read();
}
}
t0out = (buffer[1] << 8) | buffer[0];
t1out = (buffer[3] << 8) | buffer[2];
//read out h0RHx2, h1RHx2
Wire.beginTransmission(ADDRESS_HTS221);
Wire.write(H0_rH_x2 | 0x80);
Wire.endTransmission();
Wire.requestFrom(ADDRESS_HTS221, 2);
if (Wire.available() >= 2)
{
for (byte i = 0; i < 2; i++)
{
buffer[i] = Wire.read();
}
}
byte h0RHx2 = buffer[0];
byte h1RHx2 = buffer[1];
h0 = h0RHx2/2.0;
h1 = h1RHx2/2.0;
//read out h0t0Out
Wire.beginTransmission(ADDRESS_HTS221);
Wire.write(H0_T0_OUT | 0x80);
Wire.endTransmission();
Wire.requestFrom(ADDRESS_HTS221, 2);
if (Wire.available() >= 2)
{
for (byte i = 0; i < 2; i++)
{
buffer[i] = Wire.read();
}
}
h0out = (buffer[1] << 8) | buffer[0];
//read out h1t0Out
Wire.beginTransmission(ADDRESS_HTS221);
Wire.write(H1_T0_OUT | 0x80);
Wire.endTransmission();
Wire.requestFrom(ADDRESS_HTS221, 2);
if (Wire.available() >= 2)
{
for (byte i = 0; i < 2; i++)
{
buffer[i] = Wire.read();
}
}
h1out = (buffer[1] << 8) | buffer[0];
}
float mapFloat(int x, int in_min, int in_max, float out_min, float out_max)
{
return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}
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:
结论#
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