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bmp180.py
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bmp180.py
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'''
bmp180 is a micropython module for the Bosch BMP180 sensor. It measures
temperature as well as pressure, with a high enough resolution to calculate
altitude.
Breakoutboard: http://www.adafruit.com/products/1603
data-sheet: http://ae-bst.resource.bosch.com/media/products/dokumente/
bmp180/BST-BMP180-DS000-09.pdf
The MIT License (MIT)
Copyright (c) 2014 Sebastian Plamauer, oeplse@gmail.com
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
'''
from ustruct import unpack as unp
from machine import I2C, Pin
import math
import time
# BMP180 class
class BMP180():
'''
Module for the BMP180 pressure sensor.
'''
_bmp_addr = 119 # adress of BMP180 is hardcoded on the sensor
# init
def __init__(self, i2c_bus):
# create i2c obect
_bmp_addr = self._bmp_addr
self._bmp_i2c = i2c_bus
self._bmp_i2c.start()
self.chip_id = self._bmp_i2c.readfrom_mem(_bmp_addr, 0xD0, 2)
# read calibration data from EEPROM
self._AC1 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xAA, 2))[0]
self._AC2 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xAC, 2))[0]
self._AC3 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xAE, 2))[0]
self._AC4 = unp('>H', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB0, 2))[0]
self._AC5 = unp('>H', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB2, 2))[0]
self._AC6 = unp('>H', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB4, 2))[0]
self._B1 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB6, 2))[0]
self._B2 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB8, 2))[0]
self._MB = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xBA, 2))[0]
self._MC = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xBC, 2))[0]
self._MD = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xBE, 2))[0]
# settings to be adjusted by user
self.oversample_setting = 3
self.baseline = 101325.0
# output raw
self.UT_raw = None
self.B5_raw = None
self.MSB_raw = None
self.LSB_raw = None
self.XLSB_raw = None
self.gauge = self.makegauge() # Generator instance
for _ in range(128):
next(self.gauge)
time.sleep_ms(1)
def compvaldump(self):
'''
Returns a list of all compensation values
'''
return [self._AC1, self._AC2, self._AC3, self._AC4, self._AC5, self._AC6,
self._B1, self._B2, self._MB, self._MC, self._MD, self.oversample_setting]
# gauge raw
def makegauge(self):
'''
Generator refreshing the raw measurments.
'''
delays = (5, 8, 14, 25)
while True:
self._bmp_i2c.writeto_mem(self._bmp_addr, 0xF4, bytearray([0x2E]))
t_start = time.ticks_ms()
while (time.ticks_ms() - t_start) <= 5: # 5mS delay
yield None
try:
self.UT_raw = self._bmp_i2c.readfrom_mem(self._bmp_addr, 0xF6, 2)
except:
yield None
self._bmp_i2c.writeto_mem(self._bmp_addr, 0xF4, bytearray([0x34+(self.oversample_setting << 6)]))
t_pressure_ready = delays[self.oversample_setting]
t_start = time.ticks_ms()
while (time.ticks_ms() - t_start) <= t_pressure_ready:
yield None
try:
self.MSB_raw = self._bmp_i2c.readfrom_mem(self._bmp_addr, 0xF6, 1)
self.LSB_raw = self._bmp_i2c.readfrom_mem(self._bmp_addr, 0xF7, 1)
self.XLSB_raw = self._bmp_i2c.readfrom_mem(self._bmp_addr, 0xF8, 1)
except:
yield None
yield True
def blocking_read(self):
if next(self.gauge) is not None: # Discard old data
pass
while next(self.gauge) is None:
pass
@property
def oversample_sett(self):
return self.oversample_setting
@oversample_sett.setter
def oversample_sett(self, value):
if value in range(4):
self.oversample_setting = value
else:
print('oversample_sett can only be 0, 1, 2 or 3, using 3 instead')
self.oversample_setting = 3
@property
def temperature(self):
'''
Temperature in degree C.
'''
next(self.gauge)
try:
UT = unp('>H', self.UT_raw)[0]
except:
return 0.0
X1 = (UT-self._AC6)*self._AC5/2**15
X2 = self._MC*2**11/(X1+self._MD)
self.B5_raw = X1+X2
return (((X1+X2)+8)/2**4)/10
@property
def pressure(self):
'''
Pressure in mbar.
'''
next(self.gauge)
self.temperature # Populate self.B5_raw
try:
MSB = unp('B', self.MSB_raw)[0]
LSB = unp('B', self.LSB_raw)[0]
XLSB = unp('B', self.XLSB_raw)[0]
except:
return 0.0
UP = ((MSB << 16)+(LSB << 8)+XLSB) >> (8-self.oversample_setting)
B6 = self.B5_raw-4000
X1 = (self._B2*(B6**2/2**12))/2**11
X2 = self._AC2*B6/2**11
X3 = X1+X2
B3 = ((int((self._AC1*4+X3)) << self.oversample_setting)+2)/4
X1 = self._AC3*B6/2**13
X2 = (self._B1*(B6**2/2**12))/2**16
X3 = ((X1+X2)+2)/2**2
B4 = abs(self._AC4)*(X3+32768)/2**15
B7 = (abs(UP)-B3) * (50000 >> self.oversample_setting)
if B7 < 0x80000000:
pressure = (B7*2)/B4
else:
pressure = (B7/B4)*2
X1 = (pressure/2**8)**2
X1 = (X1*3038)/2**16
X2 = (-7357*pressure)/2**16
return pressure+(X1+X2+3791)/2**4
@property
def altitude(self):
'''
Altitude in m.
'''
try:
p = -7990.0*math.log(self.pressure/self.baseline)
except:
p = 0.0
return p