rpi_envsens/bmp.py

import time

from . import logger, background_task
try:
    import smbus
except ImportError:
    logger.warning("Could not import smbus. DEBUG set to True.")
    DEBUG = True
else:
    from . import DEBUG


class bmp_180(background_task):
	RUN_SLEEP_TIME = 0.5
	SMBUS_DELAY = 0.5
	MIN_REFRESH_RATE = RUN_SLEEP_TIME + 3 * SMBUS_DELAY
	KEY_TEMPERATURE = 'temperature'
	KEY_PRESSURE = 'pressure'
	KEY_TIME = 'time'
	
	def __init__(self, data_callback=None):
		self.__data_callback__ = data_callback
		# Initialise background_task
		background_task.__init__(self)
	
	def __run__(self):
		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)
	
	def __bmp_data_transmission__(self):
		if not DEBUG:
			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(self.SMBUS_DELAY)
			
			# BMP180 address, 0x77(119)
			# Select measurement control register, 0xF4(244)
			#		0x2E(46)	Enable temperature measurement
			bus.write_byte_data(0x77, 0xF4, 0x2E)
			
			time.sleep(self.SMBUS_DELAY)
			
			# 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(self.SMBUS_DELAY)
			
			# 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] = int(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
		else:
			time.sleep(3 * self.SMBUS_DELAY)
			return {
				self.KEY_PRESSURE: 1717.,
				self.KEY_TEMPERATURE: 17.17,
				self.KEY_TIME: int(time.time())
			}