/*
  从BMP180传感器读取温度与气压数据。
  通过Serial.print命令以9600波特率发送至串口监视器。
 */
 
#include <Wire.h>
#define BMP180_ADDRESS 0x77  // BMP180的I2C地址
const unsigned char OSS = 0;  // 采样设置
 
// 校准值
int ac1;
int ac2; 
int ac3; 
unsigned int ac4;
unsigned int ac5;
unsigned int ac6;
int b1; 
int b2;
int mb;
int mc;
int md;
 
// b5用于计算bmp180GetTemperature(...)，它也同时用于bmp180GetPressure(...)
// 所以Temperature(...)必须在Pressure(...)之前声明
 
long b5; 
short temperature;
long pressure;
 
void setup()
{
  Serial.begin(9600);
  Wire.begin();
  bmp180Calibration();
}
 
void loop()
{
  temperature = bmp180GetTemperature(bmp180ReadUT());
  pressure = bmp180GetPressure(bmp180ReadUP());
  Serial.print("Temperature: ");
  Serial.print(temperature, DEC);
  Serial.println(" *0.1 deg C");
  Serial.print("Pressure: ");
  Serial.print(pressure, DEC);
  Serial.println(" Pa");
  Serial.println();
  delay(1000);
}
 
// 存储所有的BMP180的校准值到全局变量
// 校准值用来计算温度与气压
// 这个函数应该放在程序的开头
 
void bmp180Calibration()
{
  ac1 = bmp180ReadInt(0xAA);
  ac2 = bmp180ReadInt(0xAC);
  ac3 = bmp180ReadInt(0xAE);
  ac4 = bmp180ReadInt(0xB0);
  ac5 = bmp180ReadInt(0xB2);
  ac6 = bmp180ReadInt(0xB4);
  b1 = bmp180ReadInt(0xB6);
  b2 = bmp180ReadInt(0xB8);
  mb = bmp180ReadInt(0xBA);
  mc = bmp180ReadInt(0xBC);
  md = bmp180ReadInt(0xBE);
}
 
// 计算温度赋值给变量ut
// 返回值的精度在0.1摄氏度
 
short bmp180GetTemperature(unsigned int ut)
{
  long x1, x2;
  x1 = (((long)ut - (long)ac6)*(long)ac5) >> 15;
  x2 = ((long)mc << 11)/(x1 + md);
  b5 = x1 + x2;
  return ((b5 + 8)>>4);  
}
 
// 计算压力
// 校准值必须是已知的
// B5在bmp180GetTemperature（...）需要使用，所以必须先调用。
// 返回值以Pa为单位
 
long bmp180GetPressure(unsigned long up)
 
{
  long x1, x2, x3, b3, b6, p;
  unsigned long b4, b7;
  b6 = b5 - 4000;
  // 计算B3
  x1 = (b2 * (b6 * b6)>>12)>>11;
  x2 = (ac2 * b6)>>11;
  x3 = x1 + x2;
  b3 = (((((long)ac1)*4 + x3)<<OSS) + 2)>>2;
  // 计算B4
  x1 = (ac3 * b6)>>13;
  x2 = (b1 * ((b6 * b6)>>12))>>16;
  x3 = ((x1 + x2) + 2)>>2;
  b4 = (ac4 * (unsigned long)(x3 + 32768))>>15;
  b7 = ((unsigned long)(up - b3) * (50000>>OSS));
  if (b7 < 0x80000000)
    p = (b7<<1)/b4;
  else
    p = (b7/b4)<<1;
  x1 = (p>>8) * (p>>8);
  x1 = (x1 * 3038)>>16;
  x2 = (-7357 * p)>>16;
  p += (x1 + x2 + 3791)>>4;
  return p;
}
 
// 在BMP180的'address'中读取一个字节
char bmp180Read(unsigned char address)
{
  unsigned char data;
  Wire.beginTransmission(BMP180_ADDRESS);
  Wire.write(address);
  Wire.endTransmission();
  Wire.requestFrom(BMP180_ADDRESS, 1);
  while(!Wire.available())  ;
  return Wire.read();
}
// 从BMP180读取两个字节
// 第一个字节是从'address'
// 第二个字节是从'address'+1
int bmp180ReadInt(unsigned char address)
{
  unsigned char msb, lsb;
  Wire.beginTransmission(BMP180_ADDRESS);
  Wire.write(address);
  Wire.endTransmission();
  Wire.requestFrom(BMP180_ADDRESS, 2);
  while(Wire.available()<2);
  msb = Wire.read();
  lsb = Wire.read();
  return (int) msb<<8 | lsb;
}
 
// 读取未补偿的温度值
unsigned int bmp180ReadUT()
 
{
  unsigned int ut;
  // 在寄存器0xF4写入0x2E
  // 这个用来请求进行温度读取
  Wire.beginTransmission(BMP180_ADDRESS);
 
  Wire.write(0xF4);
 
  Wire.write(0x2E);
  Wire.endTransmission();
  // 至少等待4.5ms
  delay(5);
  // 从寄存器0xF6与0xF7读取两个字节
  ut = bmp180ReadInt(0xF6);
  return ut;
}
 
// 读取未补偿的压力值
unsigned long bmp180ReadUP()
{
  unsigned char msb, lsb, xlsb;
  unsigned long up = 0;
  // 写入0x34+(OSS<<6)到寄存器0xF4
  // 请求气压数据读取
  Wire.beginTransmission(BMP180_ADDRESS);
  Wire.write(0xF4);
  Wire.write(0x34 + (OSS<<6));
  Wire.endTransmission();
  // 等待转换，延迟时间依赖于OSS
  delay(2 + (3<<OSS));
  // 读取寄存器0xF6 (MSB), 0xF7 (LSB), and 0xF8 (XLSB)
  Wire.beginTransmission(BMP180_ADDRESS);
  Wire.write(0xF6);
  Wire.endTransmission();
  Wire.requestFrom(BMP180_ADDRESS, 3);
  // 等待数据变为可用
  while(Wire.available() < 3);
  msb = Wire.read();
  lsb = Wire.read();
  xlsb = Wire.read();
  up = (((unsigned long) msb << 16) | ((unsigned long) lsb << 8) | (unsigned long) xlsb) >> (8-OSS);
  return up;
}