树莓派开发专栏（点击传送门）

上一篇：《树莓派开发笔记(七)：GPIO口的SPI使用(BME280三合一传感器：测量温度、湿度、气压、海拔高度) 》

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前话

前面介绍了SPI的使用，本章节我们开发GPIO口的I2C使用，同样适用BME280三合一传感器，采集气压、温度、适度，计算海拔高度。

Demo：GPIO口的I2C通讯

I2C总线是由Philips公司开发的一种简单、双向二线制同步串行总线。它只需要两根线即可在连接于总线上的器件之间传送信息。

主器件用于启动总线传送数据，并产生时钟以开放传送的器件，此时任何被寻址的器件均被认为是从器件．在总线上主和从、发和收的关系不是恒定的，而取决于此时数据传送方向：

如果主机要发送数据给从器件，则主机首先寻址从器件，然后主动发送数据至从器件，最后由主机终止数据传送；
如果主机要接收从器件的数据，则主机器件寻址从器件．然后主机接收从器件发送的数据，最后由主机终止接收过程。在这种情况下，主机主要是负责产生定时时钟和终止数据传送。

BME280

BME280是一款集成温度、湿度、气压，三位一体的环境传感器。具有高精度，多功能，小尺寸等特点，如下图：

BME280模块，设备地址默认为0x77。下面是读取数据的指令，数据的读出是从0xf7到0xfc读做（温度和压力）或从0xf7到0xfe（温度、压力、湿度等）数据以无符号形式读出。

制指令集，如下图：

读取数据指令集，分为压力，温度，适度，如下图：

开启I2C接口

sudo raspi-config

按照下图步骤选取

然后重启。

查看系统是否启动i2c，如下图：

电路原理图

检测I2C设备是否在线

我们按照图纸连接好后，使用三方查看设备是否在线来判断设备是否正常连接。

sudo apt-get install i2c-tools
sudo i2cdetect -y 1

注意：笔者对传感器不连接电源进行测试，只连接通讯的I2C线和GND（断开VCC）,使用该指令也检测不到，但是程序用wiring库却可以读到，具体原因可能是供电不足（不接VCC也供电但低于3.3V）和指令检测方式的我呢提，笔者没有细究。总之，为保持硬件稳定，需要让指令检测到才算可靠。

关键代码

初始化代码

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    _bme280.initPressureTemperatureMode();
    _bme280.initHumidity();
    startTimer(1000);
}

每隔1s读取数据

void MainWindow::timerEvent(QTimerEvent *event)
{
    ui->label_i2cP->setText(QString("%1 Pa").arg(_bme280.getPressure()));
    ui->label_i2cT->setText(QString("%1 ℃").arg(_bme280.getTemperatureC()));
    ui->label_i2cH->setText(QString("%1 %").arg(_bme280.getHumidity()));
    ui->label_i2cA->setText(QString("%1 m").arg(_bme280.getAltitudeMeters()));
}

模块代码

bme280.h

#ifndef BME280_H
#define BME280_H
#include <QObject>
#include "i2c.h"
//Register names:
#define BME280_DIG_T1_LSB_REG     0x88
#define BME280_DIG_T1_MSB_REG     0x89
#define BME280_DIG_T2_LSB_REG     0x8A
#define BME280_DIG_T2_MSB_REG     0x8B
#define BME280_DIG_T3_LSB_REG     0x8C
#define BME280_DIG_T3_MSB_REG     0x8D
#define BME280_DIG_P1_LSB_REG     0x8E
#define BME280_DIG_P1_MSB_REG     0x8F
#define BME280_DIG_P2_LSB_REG     0x90
#define BME280_DIG_P2_MSB_REG     0x91
#define BME280_DIG_P3_LSB_REG     0x92
#define BME280_DIG_P3_MSB_REG     0x93
#define BME280_DIG_P4_LSB_REG     0x94
#define BME280_DIG_P4_MSB_REG     0x95
#define BME280_DIG_P5_LSB_REG     0x96
#define BME280_DIG_P5_MSB_REG     0x97
#define BME280_DIG_P6_LSB_REG     0x98
#define BME280_DIG_P6_MSB_REG     0x99
#define BME280_DIG_P7_LSB_REG     0x9A
#define BME280_DIG_P7_MSB_REG     0x9B
#define BME280_DIG_P8_LSB_REG     0x9C
#define BME280_DIG_P8_MSB_REG     0x9D
#define BME280_DIG_P9_LSB_REG     0x9E
#define BME280_DIG_P9_MSB_REG     0x9F
#define BME280_DIG_H1_REG       0xA1
#define BME280_CHIP_ID_REG        0xD0 //Chip ID Online value is 0x60 all the time
#define BME280_RST_REG          0xE0 //Softreset Reg
#define BME280_DIG_H2_LSB_REG     0xE1
#define BME280_DIG_H2_MSB_REG     0xE2
#define BME280_DIG_H3_REG       0xE3
#define BME280_DIG_H4_MSB_REG     0xE4
#define BME280_DIG_H4_LSB_REG     0xE5
#define BME280_DIG_H5_MSB_REG     0xE6
#define BME280_DIG_H6_REG       0xE7
#define BME280_CTRL_HUMIDITY_REG    0xF2 //Ctrl Humidity Reg
#define BME280_STAT_REG         0xF3 //Status Reg
#define BME280_CTRL_MEAS_REG      0xF4 //Ctrl Measure Reg
#define BME280_CONFIG_REG       0xF5 //Configuration Reg
#define BME280_PRESSURE_MSB_REG     0xF7 //Pressure MSB
#define BME280_PRESSURE_LSB_REG     0xF8 //Pressure LSB
#define BME280_PRESSURE_XLSB_REG    0xF9 //Pressure XLSB
#define BME280_TEMPERATURE_MSB_REG    0xFA //Temperature MSB
#define BME280_TEMPERATURE_LSB_REG    0xFB //Temperature LSB
#define BME280_TEMPERATURE_XLSB_REG   0xFC //Temperature XLSB
#define BME280_HUMIDITY_MSB_REG     0xFD //Humidity MSB
#define BME280_HUMIDITY_LSB_REG     0xFE //Humidity LSB
class BME280 : public QObject
{
    Q_OBJECT
public:
    enum PRESSURE_OVERSAMPLING
    {
        PRESSURE_OVERSAMPLING_SKIPPED         = 0x00,
        PRESSURE_OVERSAMPLING_PLUS_ONE        = 0x01,
        PRESSURE_OVERSAMPLING_PLUS_TWO        = 0x02,
        PRESSURE_OVERSAMPLING_PLUS_FOUR       = 0x03,
        PRESSURE_OVERSAMPLING_PLUS_EIGHT      = 0x04,
        PRESSURE_OVERSAMPLING_PLUS_SIXTEEN    = 0x05
    };
    enum TEMPERATURE_OVERSAMPLING
    {
        TEMPERATURE_OVERSAMPLING_SKIPPED      = 0x00,
        TEMPERATURE_OVERSAMPLING_PLUS_ONE     = 0x01,
        TEMPERATURE_OVERSAMPLING_PLUS_TWO     = 0x02,
        TEMPERATURE_OVERSAMPLING_PLUS_FOUR    = 0x03,
        TEMPERATURE_OVERSAMPLING_PLUS_EIGHT   = 0x04,
        TEMPERATURE_OVERSAMPLING_PLUS_SIXTEEN = 0x05
    };
    enum MODE_OF_PRESSURE_TEMPERATUR
    {
        MODE_OF_PRESSURE_TEMPERATUR_SLEEP     = 0x00,
        MODE_OF_PRESSURE_TEMPERATUR_FORCED    = 0x01,
        MODE_OF_PRESSURE_TEMPERATUR_MORMAL    = 0x03
    };
    enum HUMIDITY_OVERSAMPLING
    {
        HUMIDITY_OVERSAMPLING_SKIPPED        = 0x00,
        HUMIDITY_OVERSAMPLING_PLUS_ONE       = 0x01,
        HUMIDITY_OVERSAMPLING_PLUS_TWO       = 0x02,
        HUMIDITY_OVERSAMPLING_PLUS_FOUR      = 0x03,
        HUMIDITY_OVERSAMPLING_PLUS_EIGHT     = 0x04,
        HUMIDITY_OVERSAMPLING_PLUS_SIXTEEN   = 0x05
    };
    struct Calibration
    {
        uint16_t dig_T1;
        int16_t dig_T2;
        int16_t dig_T3;
        uint16_t dig_P1;
        int16_t dig_P2;
        int16_t dig_P3;
        int16_t dig_P4;
        int16_t dig_P5;
        int16_t dig_P6;
        int16_t dig_P7;
        int16_t dig_P8;
        int16_t dig_P9;
        uint8_t dig_H1;
        int16_t dig_H2;
        uint8_t dig_H3;
        int16_t dig_H4;
        int16_t dig_H5;
        uint8_t dig_H6;
    };
public:
    explicit BME280(int devId = 0x77, QObject *parent = 0);
    bool isOnline();
    void initPressureTemperatureMode(
            PRESSURE_OVERSAMPLING p = PRESSURE_OVERSAMPLING_PLUS_ONE,
            TEMPERATURE_OVERSAMPLING t = TEMPERATURE_OVERSAMPLING_PLUS_ONE,
            MODE_OF_PRESSURE_TEMPERATUR m = MODE_OF_PRESSURE_TEMPERATUR_MORMAL);
    void initHumidity(HUMIDITY_OVERSAMPLING h = HUMIDITY_OVERSAMPLING_PLUS_ONE);
    void reset();
public slots:
    float getTemperatureC();
    float getTemperatureF();
    float getPressure();
    float getHumidity();
    float getAltitudeMeters();
    float getAltitudeFeet();
private:
    I2c _i2c;
    int _devId;
    Calibration _calibration;
    int32_t _tFine;
};
#endif // BME280_H

bme280.cpp

#include "bme280.h"
#include <QDebug>
BME280::BME280(int devId, QObject *parent)
    : QObject(parent),
      _devId(devId)
{
    _i2c.open(devId);
    …
}
bool BME280::isOnline()
{
    // according to 0xD0 "id", value is 0x60
    return _i2c.readData(BME280_CHIP_ID_REG) == 0x60;
}
void BME280::initPressureTemperatureMode(BME280::PRESSURE_OVERSAMPLING p, BME280::TEMPERATURE_OVERSAMPLING t, BME280::MODE_OF_PRESSURE_TEMPERATUR m)
{
    uchar uc;
    …
    _i2c.writeData(BME280_CTRL_MEAS_REG, uc);
    _i2c.readData(BME280_CTRL_MEAS_REG);
    …
}
void BME280::initHumidity(BME280::HUMIDITY_OVERSAMPLING h)
{
    uchar uc;
    …
    _i2c.writeData(BME280_CTRL_HUMIDITY_REG, uc);
}
void BME280::reset()
{
    _i2c.writeData(BME280_RST_REG, 0xB6);
}
float BME280::getTemperatureC()
{
    …
    int32_t adc_T = ((uint32_t)_i2c.readData(BME280_TEMPERATURE_MSB_REG) << 12) | ((uint32_t)_i2c.readData(BME280_TEMPERATURE_LSB_REG) << 4) | ((_i2c.readData(BME280_TEMPERATURE_XLSB_REG) >> 4) & 0x0F);
    …
    float output = (_tFine * 5 + 128) >> 8;
    output = output / 100;
    return output;
}
float BME280::getTemperatureF()
{
    float output = getTemperatureC();
    output = (output * 9) / 5 + 32;
    return output;
}
float BME280::getPressure()
{
   …
   int32_t adc_P = ((uint32_t)_i2c.readData(BME280_PRESSURE_MSB_REG) << 12) | ((uint32_t)_i2c.readData(BME280_PRESSURE_LSB_REG) << 4) | ((_i2c.readData(BME280_PRESSURE_XLSB_REG) >> 4) & 0x0F);
    int64_t var1, var2, p_acc;
    …
    p_acc = p_acc >> 8; // /256
    return (float)p_acc;
}
float BME280::getHumidity()
{
    …
    int32_t adc_H = ((uint32_t)_i2c.readData(BME280_HUMIDITY_MSB_REG) << 8) | ((uint32_t)_i2c.readData(BME280_HUMIDITY_LSB_REG));
    int32_t var1;
    …
    return (float)((var1>>12) >> 10);
}
float BME280::getAltitudeMeters()
{
    float heightOutput = 0;
    …
    return heightOutput;
}
float BME280::getAltitudeFeet()
{
    float heightOutput = 0;
    heightOutput = getAltitudeMeters() * 3.28084;
    return heightOutput;
}

I2C模块代码

i2c.h

#ifndef I2C_H
#define I2C_H
#include <QObject>
#include <QByteArray>
class I2c : public QObject
{
    Q_OBJECT
public:
    explicit I2c(QObject *parent = 0);
signals:
public slots:
    bool open(uchar addr);
    void writeData(int reg, uchar data);
    uchar readData(int reg);
private:
    int _fd;
};
#endif // I2C_H

i2c.cpp

#include "i2c.h"
#include "wiringPi.h"
#include "wiringPiI2C.h"
#include <QDebug>
#include <QByteArray>
I2c::I2c(QObject *parent) : QObject(parent)
{
    wiringPiSetup();
    _fd = 0;
}
bool I2c::open(uchar addr)
{
_fd = wiringPiI2CSetup(addr);
…
}
void I2c::writeData(int reg, uchar data)
{
    …
    ret = wiringPiI2CWriteReg8(_fd, reg, data);
}
uchar I2c::readData(int reg)
{
    …
    data = wiringPiI2CReadReg8(_fd, reg);
    …
}