Raspberry Pi 筆記(76)：溫度氣壓傳感器模組 BMP180 (GY68)

曾經實做過Arduino讀取 BMP180的溫度、大氣壓力及海拔高度： Arduino筆記(70)：溫度氣壓傳感器模組 BMP180 (GY68) 。本篇先從實做樹莓派讀取感測器的值，顯示在終端視窗上。下一篇會實做將讀到值要送到 Line Notify中，直接從 Line  中看到相關的感測值。

BMP180 是Bosch Sensortec 新推出的數字氣壓傳感器，性能非常高，可用於智能手機，平板電腦和運動設備等高級移動設備。像大多數壓力傳感器一樣，BMP180可以測量絕對壓力，這是設備看到的實際環境壓力，隨海拔高度和天氣而變化。

[材料]

• Raspberry Pi x 1
• BMP180 (GY68)  x 1
• 連接線 x 4條

[接線圖]

Raspberry Pi 與BMP180接腳的對應關係：

Pi 接腳	BMP180
Pin 1(+3.3V)	VCC
Pin 6(GND)	GND
Pin 3 SDA GPIO2	SDA
Pin 5 SCL GPIO3	SCL

[程式]

# !/usr/bin/python
# coding:utf-8

import smbus
import time
from ctypes import c_short

DEVICE = 0x77      # 預設 I2C 位址

#bus = smbus.SMBus(0)  # Rev 1 Pi uses 0
bus = smbus.SMBus(1)  # Rev 2 Pi uses 1 

def convertToString(data):
  # Simple function to convert binary data into a string
  return str((data[1] + (256 * data[0])) / 1.2)

def getShort(data, index):
  # return two bytes from data as a signed 16-bit value
  return c_short((data[index] << 8) + data[index + 1]).value

def getUshort(data, index):
  # return two bytes from data as an unsigned 16-bit value
  return (data[index] << 8) + data[index + 1]

def readBmp180Id(addr=DEVICE):
  # Register Address
  REG_ID     = 0xD0

  (chip_id, chip_version) = bus.read_i2c_block_data(addr, REG_ID, 2)
  return (chip_id, chip_version)
  
def readBmp180(addr=DEVICE):
  # Register Addresses
  REG_CALIB  = 0xAA
  REG_MEAS   = 0xF4
  REG_MSB    = 0xF6
  REG_LSB    = 0xF7
  # Control Register Address
  CRV_TEMP   = 0x2E
  CRV_PRES   = 0x34 
  # Oversample setting
  OVERSAMPLE = 3    # 0 - 3
  
  # Read calibration data
  # Read calibration data from EEPROM
  cal = bus.read_i2c_block_data(addr, REG_CALIB, 22)

  # Convert byte data to word values
  AC1 = getShort(cal, 0)
  AC2 = getShort(cal, 2)
  AC3 = getShort(cal, 4)
  AC4 = getUshort(cal, 6)
  AC5 = getUshort(cal, 8)
  AC6 = getUshort(cal, 10)
  B1  = getShort(cal, 12)
  B2  = getShort(cal, 14)
  MB  = getShort(cal, 16)
  MC  = getShort(cal, 18)
  MD  = getShort(cal, 20)

  # 讀取溫度
  bus.write_byte_data(addr, REG_MEAS, CRV_TEMP)
  time.sleep(0.005)
  (msb, lsb) = bus.read_i2c_block_data(addr, REG_MSB, 2)
  UT = (msb << 8) + lsb

  # 讀取壓力
  bus.write_byte_data(addr, REG_MEAS, CRV_PRES + (OVERSAMPLE << 6))
  time.sleep(0.04)
  (msb, lsb, xsb) = bus.read_i2c_block_data(addr, REG_MSB, 3)
  UP = ((msb << 16) + (lsb << 8) + xsb) >> (8 - OVERSAMPLE)

  # Refine temperature
  X1 = ((UT - AC6) * AC5) >> 15
  X2 = (MC << 11) / (X1 + MD)
  B5 = X1 + X2
  temperature = (B5 + 8) >> 4

  # Refine pressure
  B6  = B5 - 4000
  B62 = B6 * B6 >> 12
  X1  = (B2 * B62) >> 11
  X2  = AC2 * B6 >> 11
  X3  = X1 + X2
  B3  = (((AC1 * 4 + X3) << OVERSAMPLE) + 2) >> 2

  X1 = AC3 * B6 >> 13
  X2 = (B1 * B62) >> 16
  X3 = ((X1 + X2) + 2) >> 2
  B4 = (AC4 * (X3 + 32768)) >> 15
  B7 = (UP - B3) * (50000 >> OVERSAMPLE)

  P = (B7 * 2) / B4

  X1 = (P >> 8) * (P >> 8)
  X1 = (X1 * 3038) >> 16
  X2 = (-7357 * P) >> 16
  pressure = P + ((X1 + X2 + 3791) >> 4)

  # 計算高度
  altitude = 44330.0 * (1.0 - pow(pressure / 101325.0, (1.0/5.255)))
  return (temperature/10.0,pressure/ 100.0,round(altitude,2))

def main():

  (chip_id, chip_version) = readBmp180Id()
  print "Chip ID     :", chip_id
  print "Version     :", chip_version,"\n"
  # 連續偵測 5次
  for i in range(0,5):
     (temperature,pressure,altitude)=readBmp180()
     print "溫度 :", temperature, "C"
     print "壓力 :", pressure, "mbar"
     print "高度 :", altitude, "m\n"
     time.sleep(2)

if __name__=="__main__":   
  main()
  time.sleep(2)

[執行結果]

[參考資料]

• Home Temperature Monitoring Using Raspberry Pi and Thingspeak
• BMP180 Digital Pressure Sensor with Raspberry Pi