BMP180 is a nice tiny sensor which can give the values of

  • Atmospheric Pressure
  • Temperature
  • Altitude

In this video, we’ll see how we can interface Raspberry pi with BMP180 and how to write python code for the same.

In order to follow this video you’ll need

  • Raspberry Pi 2/3/4 with Raspbian OS Installed on it
  • BMP180 Sensor
  • Female to Female Wire connectors

For setting up the raspberry pi and start using it, you can follow this post. 

How to interface I2C Sensor with Raspberry Pi

Python Program to interface raspberry pi with BMP180.

The video shows about 2 different programs one is the library package and other is testing code. Make sure while testing out, both the programs stay in the same folder.

Here are the 2 programs

Python Program for BMP180 Sensor Part 1

# make sure to install python-smbus using below command
# sudo apt-get install python-smbus
import smbus
import time
from ctypes import c_short
 
DEVICE = 0x77 # Default device I2C address
 
#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):
  # Chip ID 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=0x77):
  # 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)

  # Read temperature
  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

  # Read pressure
  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 = int(B5 + 8) >> 4
  temperature = temperature / 10.0

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

  X1 = int(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 = (int(P) >> 8) * (int(P) >> 8)
  X1 = (X1 * 3038) >> 16
  X2 = int(-7357 * P) >> 16
  pressure = int(P + ((X1 + X2 + 3791) >> 4))
  #pressure = float(pressure / 100.0)
  
  
  altitude = 44330.0 * (1.0 - pow(pressure / 101325.0, (1.0/5.255)))
  altitude = round(altitude,2)

  return (temperature,pressure,altitude)

Python Program for BMP180 Sensor Part 2

import bmpsensor
import time
while True:
    temp, pressure, altitude = bmpsensor.readBmp180()
    print("Temperature is ",temp)  # degC
    print("Pressure is ",pressure) # Pressure in Pa 
    print("Altitude is ",altitude) # Altitude in meters
    print("\n")
    time.sleep(2)

 

If you face any issues with the code or working or explanation, feel free to comment about it!!

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