rpi_envsens/bmp.py

# Distributed with a free-will license.
# Use it any way you want, profit or free, provided it fits in the licenses of its associated works.
# BMP180
# This code is designed to work with the BMP180_I2CS I2C Mini Module available from ControlEverything.com.
# https://www.controleverything.com/content/Pressure?sku=BMP180_I2CS#tabs-0-product_tabset-2

import smbus
import threading
import time

from . import logger


class bmp_180(object):
	KEY_TEMPERATURE = 'temperature'
	KEY_PRESSURE = 'pressure'
	KEY_TIME = 'time'
	
	def __init__(self, data_callback=None):
		self.__data_callback__ = data_callback
		# Initial the dht device, with data pin connected to:
		self.__active__ = True
		self.__thread__ = threading.Thread(target=self.run, args=())
		self.__thread__.daemon = True                            # Daemonize thread
		self.__thread__.start()                                  # Start the execution
	
	def run(self):
		while self.__active__:
			data = self.__bmp_data_transmission__()
			if data is not None:
				logger.debug('BMP-Communication: Successfully: %s', repr(data))
				if self.__data_callback__ is not None:
					self.__data_callback__(**data)
			time.sleep(0.5)
	
	def close(self):
		self.__active__ = False
		self.__thread__.join()
	
	def __del__(self):
		self.close()
	
	def __bmp_data_transmission__(self):
		rv = {}
		# Get I2C bus
		bus = smbus.SMBus(1)
		
		# BMP180 address, 0x77(119)
		# Read data back from 0xAA(170), 22 bytes
		data = bus.read_i2c_block_data(0x77, 0xAA, 22)
		
		# Convert the data
		AC1 = data[0] * 256 + data[1]
		if AC1 > 32767 :
			AC1 -= 65535
		AC2 = data[2] * 256 + data[3]
		if AC2 > 32767 :
			AC2 -= 65535
		AC3 = data[4] * 256 + data[5]
		if AC3 > 32767 :
			AC3 -= 65535
		AC4 = data[6] * 256 + data[7]
		AC5 = data[8] * 256 + data[9]
		AC6 = data[10] * 256 + data[11]
		B1 = data[12] * 256 + data[13]
		if B1 > 32767 :
			B1 -= 65535
		B2 = data[14] * 256 + data[15]
		if B2 > 32767 :
			B2 -= 65535
		MB = data[16] * 256 + data[17]
		if MB > 32767 :
			MB -= 65535
		MC = data[18] * 256 + data[19]
		if MC > 32767 :
			MC -= 65535
		MD = data[20] * 256 + data[21]
		if MD > 32767 :
			MD -= 65535
		
		time.sleep(0.5)
		
		# BMP180 address, 0x77(119)
		# Select measurement control register, 0xF4(244)
		#		0x2E(46)	Enable temperature measurement
		bus.write_byte_data(0x77, 0xF4, 0x2E)
		
		time.sleep(0.5)
		
		# BMP180 address, 0x77(119)
		# Read data back from 0xF6(246), 2 bytes
		# temp MSB, temp LSB
		data = bus.read_i2c_block_data(0x77, 0xF6, 2)
		
		# Convert the data
		temp = data[0] * 256 + data[1]
		
		# BMP180 address, 0x77(119)
		# Select measurement control register, 0xF4(244)
		#		0x74(116)	Enable pressure measurement, OSS = 1
		bus.write_byte_data(0x77, 0xF4, 0x74)
		
		time.sleep(0.5)
		
		# BMP180 address, 0x77(119)
		# Read data back from 0xF6(246), 3 bytes
		# pres MSB1, pres MSB, pres LSB
		data = bus.read_i2c_block_data(0x77, 0xF6, 3)
		
		rv[self.KEY_TIME] = time.time()
	
		# Convert the data
		pres = ((data[0] * 65536) + (data[1] * 256) + data[2]) / 128
		# Callibration for Temperature
		X1 = (temp - AC6) * AC5 / 32768.0
		X2 = (MC * 2048.0) / (X1 + MD)
		B5 = X1 + X2
		rv[self.KEY_TEMPERATURE] = ((B5 + 8.0) / 16.0) / 10.0
		
		# Calibration for Pressure
		B6 = B5 - 4000
		X1 = (B2 * (B6 * B6 / 4096.0)) / 2048.0
		X2 = AC2 * B6 / 2048.0
		X3 = X1 + X2
		B3 = (((AC1 * 4 + X3) * 2) + 2) / 4.0
		X1 = AC3 * B6 / 8192.0
		X2 = (B1 * (B6 * B6 / 2048.0)) / 65536.0
		X3 = ((X1 + X2) + 2) / 4.0
		B4 = AC4 * (X3 + 32768) / 32768.0
		B7 = ((pres - B3) * (25000.0))
		pressure = 0.0
		if B7 < 2147483648:
			pressure = (B7 * 2) / B4
		else :
			pressure = (B7 / B4) * 2
		X1 = (pressure / 256.0) * (pressure / 256.0)
		X1 = (X1 * 3038.0) / 65536.0
		X2 = ((-7357) * pressure) / 65536.0
		rv[self.KEY_PRESSURE] = (pressure + (X1 + X2 + 3791) / 16.0) / 100
	
		return rv