概述

在这一课中我们将学习如何用Raspberry Pi读取BMP180数字气压传感器。

所需器件

1 * Raspberry Pi
1 * Breadboard
1 * BMP180
Several jumper wires

工作原理

BMP180能够检测气压和温度,BMP180通过IIC接口输出数据,我们用Pi的IIC去读取BMP180测量到的气压值和温度值并输出在屏幕上。

原理图如下

实物连线图

没画

软件

在进行下面的步骤之前先打开Pi的IIC接口,具体操作请看lesson13,如果已经打开请跳过此步。

For C Language users, please follow the next step:

1)  在/home/pi目录下新建一个.h头文件,名字随意(你开心就好)

cd  ~

sudo  nano  bmp180.h

先向头文件中添加一下代码

#ifndef _BMP180_
#define _BMP180_

//i2c address
#define BMP180_Address 0x77

//Operating Modes
#define BMP180_ULTRALOWPOWER    0
#define BMP180_STANDARD         1
#define BMP180_HIGHRES          2
#define BMP180_ULTRAHIGHRES     3

//BMP185 Registers
#define BMP180_CAL_AC1          0xAA  //Calibration data (16 bits)
#define BMP180_CAL_AC2          0xAC  //Calibration data (16 bits)
#define BMP180_CAL_AC3          0xAE  //Calibration data (16 bits)
#define BMP180_CAL_AC4          0xB0  //Calibration data (16 bits)
#define BMP180_CAL_AC5          0xB2  //Calibration data (16 bits)
#define BMP180_CAL_AC6          0xB4  //Calibration data (16 bits)
#define BMP180_CAL_B1           0xB6  //Calibration data (16 bits)
#define BMP180_CAL_B2           0xB8  //Calibration data (16 bits)
#define BMP180_CAL_MB           0xBA  //Calibration data (16 bits)
#define BMP180_CAL_MC           0xBC  //Calibration data (16 bits)
#define BMP180_CAL_MD           0xBE  //Calibration data (16 bits)
#define BMP180_CONTROL          0xF4
#define BMP180_TEMPDATA         0xF6
#define BMP180_PRESSUREDATA     0xF6

//Commands
#define BMP180_READTEMPCMD      0x2E
#define BMP180_READPRESSURECMD  0x34

#endif

在键盘上输入Ctrl+X,在输入Y保存退出。

1) 在/home/pi目录下新建一个.c源文件,名字随意(你开心就好)

cd  ~

sudo  nano  bmp180test.c

向新建的源文件中添加一下代码

#include 
#include 
#include 
#include 
#include "bmp180.h"

#define OSS BMP180_STANDARD
short AC1,AC2,AC3,B1,B2,MB,MC,MD;
unsigned short AC4,AC5,AC6;
int fd;
char I2C_readByte(int reg)
{
    return (char)wiringPiI2CReadReg8(fd,reg);
}

unsigned short I2C_readU16(int reg)
{
    int MSB,LSB;
    MSB = I2C_readByte(reg);
    LSB = I2C_readByte(reg + 1);
    int value = (MSB << 8) +LSB; return (unsigned short)value; } short I2C_readS16(int reg) { int result; result = I2C_readU16(reg); if (result > 32767)result -= 65536;
    return (short)result;
}
void I2C_writeByte(int reg,int val)
{
    wiringPiI2CWriteReg8(fd,reg,val);
}

void load_calibration()
{
    AC1 = I2C_readS16(BMP180_CAL_AC1);
    AC2 = I2C_readS16(BMP180_CAL_AC2);
    AC3 = I2C_readS16(BMP180_CAL_AC3);
    AC4 = I2C_readU16(BMP180_CAL_AC4);
    AC5 = I2C_readU16(BMP180_CAL_AC5);
    AC6 = I2C_readU16(BMP180_CAL_AC6);
    B1  = I2C_readS16(BMP180_CAL_B1);
    B2  = I2C_readS16(BMP180_CAL_B2);
    MB  = I2C_readS16(BMP180_CAL_MB);
    MC  = I2C_readS16(BMP180_CAL_MC);
    MD  = I2C_readS16(BMP180_CAL_MD);
}
int read_raw_temp()
{
    int raw;
    I2C_writeByte(BMP180_CONTROL,BMP180_READTEMPCMD);
    delay(5);  //5ms;
    raw = I2C_readByte(BMP180_TEMPDATA) << 8;
    raw += I2C_readByte(BMP180_TEMPDATA+1);
    return raw;

}
int read_raw_pressure()
{
    int MSB,LSB,XLSB,raw;
    I2C_writeByte(BMP180_CONTROL,BMP180_READPRESSURECMD +(OSS << 6));
    switch(OSS)
    {
        case BMP180_ULTRALOWPOWER:
            delay(5);break;
        case BMP180_HIGHRES:
            delay(14);break;
        case BMP180_ULTRAHIGHRES:
            delay(26);break;
        default :
            delay(8);
    }
    MSB  = I2C_readByte(BMP180_PRESSUREDATA);
    LSB  = I2C_readByte(BMP180_PRESSUREDATA + 1);
    XLSB = I2C_readByte(BMP180_PRESSUREDATA + 2);
    raw = ((MSB << 16) + (LSB << 8) + XLSB) >> (8 - OSS);
    return raw;
}
float read_temperature()
{
    float T;
    int UT,X1,X2,B5;
    UT = read_raw_temp();
    X1 = ((UT - AC6)*AC5) >> 15;
    X2 = (MC << 11) / (X1 + MD); B5 = X1 + X2; T = ((B5 + 8) >> 4) /10.0;
    return T;
}

int read_pressure()
{
    int P;
    int UT,UP,X1,X2,X3,B3,B5,B6;
    unsigned int B4;
    int B7;
    UT = read_raw_temp();
    UP = read_raw_pressure();

    X1 = ((UT - AC6)*AC5) >> 15;
    X2 = (MC << 11) / (X1 + MD); B5 = X1 + X2; //Pressure Calculations B6 = B5 - 4000; X1 = (B2 * (B6 * B6) >> 12) >> 11;
    X2 = (AC2 * B6) >> 11;
    X3 = X1 + X2;
    B3 = (((AC1 * 4 + X3) << OSS) + 2) / 4; X1 = (AC3 * B6) >> 13;
    X2 = (B1 * ((B6 * B6) >> 12)) >> 16;
    X3 = ((X1 + X2) + 2) >> 2;
    B4 = (AC4 * (X3 + 32768)) >> 15;
    B7 = (UP - B3) * (50000 >> OSS);
    if (B7 < 0x80000000){P = (B7 * 2) / B4;} else {P = (B7 / B4) * 2;} X1 = (P >> 8) * (P >> 8);
    X1 = (X1 * 3038) >> 16;
    X2 = (-7357 * P) >> 16;
    P = P + ((X1 + X2 + 3791) >> 4);
    return P;

}
float read_altitude()
{
    float pressure,altitude;
    float sealevel_pa = 101325.0;
    pressure = (float)read_pressure();
    altitude = 44330.0 * (1.0 - pow(pressure / sealevel_pa,(1.0/5.255)));
    return altitude;
}
float read_sealevel_pressure()
{
    float altitude_m = 0.0;
    float pressure,p0;
    pressure =(float)read_pressure();
    p0 = pressure / pow(1.0 - altitude_m/44330.0,5.255);
    return p0;
}
int main(int argc,char **argv)
{
    printf("BMP180 Test Program ...\n");
    if(wiringPiSetup() < 0) return 1;
    fd = wiringPiI2CSetup(BMP180_Address);
    load_calibration();
    while(1)
    {
        printf("\nTemperature : %.2f C\n",read_temperature());
        printf("Pressure :    %.2f Pa\n",read_pressure()/100.0);
        printf("Altitude :    %.2f h\n",read_altitude());
        delay(1000);
    }
    return 0;
}

在键盘上输入Ctrl+X,在输入Y保存退出。

完整的程序源码可以通过下面命令获取

wget  https://osoyoo.com/driver/pi3_start_learning_kit_lesson_18\c

2) 编译

sudo  gcc  -Wall -o  bmp180  bmp180test.c  -lwiringPi  -lm

3) 运行程序

sudo  ./bmp180 

4) 最终结果

运行上面的程序,屏幕上会输出BMP180测量到的温度值,气压值以及海拔高度。


for python users

1)我们需要安装一个工具软件(smbus)与IIC通讯

sudo apt-get install python-smbus

2) 在/home/pi下新建一个.py脚本文件,文件名随意(你爱咋咋地)

cd  ~

sudo  nano  BMP180.py

先新建的脚本文件中添加以下代码

import time
import smbus
 
# BMP085 default address.
BMP180_I2CADDR           = 0x77
 
# Operating Modes
BMP180_ULTRALOWPOWER     = 0
BMP180_STANDARD          = 1
BMP180_HIGHRES           = 2
BMP180_ULTRAHIGHRES      = 3
 
# BMP085 Registers
BMP180_CAL_AC1           = 0xAA  # R   Calibration data (16 bits)
BMP180_CAL_AC2           = 0xAC  # R   Calibration data (16 bits)
BMP180_CAL_AC3           = 0xAE  # R   Calibration data (16 bits)
BMP180_CAL_AC4           = 0xB0  # R   Calibration data (16 bits)
BMP180_CAL_AC5           = 0xB2  # R   Calibration data (16 bits)
BMP180_CAL_AC6           = 0xB4  # R   Calibration data (16 bits)
BMP180_CAL_B1            = 0xB6  # R   Calibration data (16 bits)
BMP180_CAL_B2            = 0xB8  # R   Calibration data (16 bits)
BMP180_CAL_MB            = 0xBA  # R   Calibration data (16 bits)
BMP180_CAL_MC            = 0xBC  # R   Calibration data (16 bits)
BMP180_CAL_MD            = 0xBE  # R   Calibration data (16 bits)
BMP180_CONTROL           = 0xF4
BMP180_TEMPDATA          = 0xF6
BMP180_PRESSUREDATA      = 0xF6
 
# Commands
BMP180_READTEMPCMD       = 0x2E
BMP180_READPRESSURECMD   = 0x34
 
 
class BMP180(object):
    def __init__(self, address=BMP180_I2CADDR, mode=BMP180_STANDARD):
        self._mode = mode
        self._address = address
        self._bus = smbus.SMBus(1)
        # Load calibration values.
        self._load_calibration()
    def _read_byte(self,cmd):
        return self._bus.read_byte_data(self._address,cmd)
 
    def _read_u16(self,cmd):
        MSB = self._bus.read_byte_data(self._address,cmd)
        LSB = self._bus.read_byte_data(self._address,cmd+1)
        return (MSB << 8) + LSB def _read_s16(self,cmd): result = self._read_u16(cmd) if result > 32767:result -= 65536
        return result
 
    def _write_byte(self,cmd,val):
        self._bus.write_byte_data(self._address,cmd,val)
 
    def _load_calibration(self):
        "load calibration"
        self.cal_AC1 = self._read_s16(BMP180_CAL_AC1)   # INT16
        self.cal_AC2 = self._read_s16(BMP180_CAL_AC2)   # INT16
        self.cal_AC3 = self._read_s16(BMP180_CAL_AC3)   # INT16
        self.cal_AC4 = self._read_u16(BMP180_CAL_AC4)   # UINT16
        self.cal_AC5 = self._read_u16(BMP180_CAL_AC5)   # UINT16
        self.cal_AC6 = self._read_u16(BMP180_CAL_AC6)   # UINT16
        self.cal_B1  = self._read_s16(BMP180_CAL_B1)     # INT16
        self.cal_B2  = self._read_s16(BMP180_CAL_B2)     # INT16
        self.cal_MB  = self._read_s16(BMP180_CAL_MB)     # INT16
        self.cal_MC  = self._read_s16(BMP180_CAL_MC)     # INT16
        self.cal_MD  = self._read_s16(BMP180_CAL_MD)     # INT16
 
    def read_raw_temp(self):
        """Reads the raw (uncompensated) temperature from the sensor."""
        self._write_byte(BMP180_CONTROL, BMP180_READTEMPCMD)
        time.sleep(0.005)  # Wait 5ms
        MSB = self._read_byte(BMP180_TEMPDATA)
        LSB = self._read_byte(BMP180_TEMPDATA+1)
        raw = (MSB << 8) + LSB
        return raw
 
    def read_raw_pressure(self):
        """Reads the raw (uncompensated) pressure level from the sensor."""
        self._write_byte(BMP180_CONTROL, BMP180_READPRESSURECMD + (self._mode << 6))
        if self._mode == BMP180_ULTRALOWPOWER:
            time.sleep(0.005)
        elif self._mode == BMP180_HIGHRES:
            time.sleep(0.014)
        elif self._mode == BMP180_ULTRAHIGHRES:
            time.sleep(0.026)
        else:
            time.sleep(0.008)
        MSB = self._read_byte(BMP180_PRESSUREDATA)
        LSB = self._read_byte(BMP180_PRESSUREDATA+1)
        XLSB = self._read_byte(BMP180_PRESSUREDATA+2)
        raw = ((MSB << 16) + (LSB << 8) + XLSB) >> (8 - self._mode)
        return raw
 
    def read_temperature(self):
        """Gets the compensated temperature in degrees celsius."""
        UT = self.read_raw_temp()
 
        X1 = ((UT - self.cal_AC6) * self.cal_AC5) >> 15
        X2 = (self.cal_MC << 11) / (X1 + self.cal_MD) B5 = X1 + X2 temp = ((B5 + 8) >> 4) / 10.0
        return temp
 
    def read_pressure(self):
        """Gets the compensated pressure in Pascals."""
        UT = self.read_raw_temp()
        UP = self.read_raw_pressure()
 
 
        X1 = ((UT - self.cal_AC6) * self.cal_AC5) >> 15
        X2 = (self.cal_MC << 11) / (X1 + self.cal_MD) B5 = X1 + X2 # Pressure Calculations B6 = B5 - 4000 X1 = (self.cal_B2 * (B6 * B6) >> 12) >> 11
        X2 = (self.cal_AC2 * B6) >> 11
        X3 = X1 + X2
        B3 = (((self.cal_AC1 * 4 + X3) << self._mode) + 2) / 4 X1 = (self.cal_AC3 * B6) >> 13
        X2 = (self.cal_B1 * ((B6 * B6) >> 12)) >> 16
        X3 = ((X1 + X2) + 2) >> 2
        B4 = (self.cal_AC4 * (X3 + 32768)) >> 15
        B7 = (UP - B3) * (50000 >> self._mode)
 
        if B7 < 0x80000000: p = (B7 * 2) / B4 else: p = (B7 / B4) * 2 X1 = (p >> 8) * (p >> 8)
        X1 = (X1 * 3038) >> 16
        X2 = (-7357 * p) >> 16
 
        p = p + ((X1 + X2 + 3791) >> 4)
        return p
 
    def read_altitude(self, sealevel_pa=101325.0):
        """Calculates the altitude in meters."""
        # Calculation taken straight from section 3.6 of the datasheet.
        pressure = float(self.read_pressure())
        altitude = 44330.0 * (1.0 - pow(pressure / sealevel_pa, (1.0/5.255)))
        return altitude
 
    def read_sealevel_pressure(self, altitude_m=0.0):
        """Calculates the pressure at sealevel when given a known altitude in
        meters. Returns a value in Pascals."""
        pressure = float(self.read_pressure())
        p0 = pressure / pow(1.0 - altitude_m/44330.0, 5.255)
        return p0

按键盘上Ctrl+X,再按Y保存退出。

在/home/pi下再新建一个.py脚本文件,文件名随意(你爱咋咋地)

cd  ~

sudo  nano  BMP180test.py

向这个脚本文件中添加以下代码

import time
from BMP180 import BMP180
 
# Initialise the BMP085 and use STANDARD mode (default value)
# bmp = BMP085(0x77, debug=True)
bmp = BMP180()
 
# To specify a different operating mode, uncomment one of the following:
# bmp = BMP085(0x77, 0)  # ULTRALOWPOWER Mode
# bmp = BMP085(0x77, 1)  # STANDARD Mode
# bmp = BMP085(0x77, 2)  # HIRES Mode
# bmp = BMP085(0x77, 3)  # ULTRAHIRES Mode
while True:
    temp = bmp.read_temperature()
 
# Read the current barometric pressure level
    pressure = bmp.read_pressure()
 
# To calculate altitude based on an estimated mean sea level pressure
# (1013.25 hPa) call the function as follows, but this won't be very accurate
    altitude = bmp.read_altitude()
 
# To specify a more accurate altitude, enter the correct mean sea level
# pressure level.  For example, if the current pressure level is 1023.50 hPa
# enter 102350 since we include two decimal places in the integer value
# altitude = bmp.readAltitude(102350)
 
    print "Temperature: %.2f C" % temp
    print "Pressure:    %.2f hPa" % (pressure / 100.0)
    print "Altitude:     %.2f\n" % altitude
time.sleep(2)

按键盘上Ctrl+X,再按Y保存退出。

完整代码可以下面命令获取到

wget  https://osoyoo.com/driver/pi3_start_learning_kit_lesson_18/python

3) 运行你的脚本程序

sudo python BMP180test.py

4) 最终结果

运行上面Python脚本程序,屏幕上会输出BMP180测量到的温度值、气压值以及海拔高度。