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asciiphil/MPL115A2.py

Last active Apr 10, 2021
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Python class for communicating with a MPL115A2 I2C digital barometer/temperature sensor. Uses the Adafruit_I2C class from the Adafruit Raspberry Pi Python Code: https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code .
#!/usr/bin/python
# Author: Phil! Gold <phil_g@pobox.com>
# License: CC0 Waiver http://creativecommons.org/publicdomain/zero/1.0/
import time
from Adafruit_I2C import Adafruit_I2C
class _MPL115A2_Register:
# Each register is two bytes wide, with the values left-aligned in the
# register.
# TOTAL_BITS gives the total number of data bits (and is used to calculate
# how much right shifting is needed to eliminate the padding).
# SIGN_BITS is the number of bits reserved for sign information and
# determines whether the value is read as a signed or unsigned number.
# FRACTIONAL_BITS gives the number of bits that should be considered to
# follow the decimal point.
# DECIMAL_ZERO_PADDING gives the number of additional zero bits that should
# be considered to exist between the decimal point and the first data bit.
def __init__(self, address, total_bits, sign_bits, fractional_bits, decimal_zero_padding):
self.address = address
self.total_bits = total_bits
self.sign_bits = sign_bits
self.fractional_bits = fractional_bits
self.decimal_zero_padding = decimal_zero_padding
def read(self, i2c):
# Get the data from the register.
raw_value = i2c.readU16(self.address)
# Negative values are stored in two's-complement
if self.sign_bits == 1 and raw_value & 0x8000:
raw_value = raw_value ^ 0xFFFF * -1
# Apply the bit parameters.
return (raw_value >> (16 - self.total_bits)) / float(2**(self.fractional_bits+self.decimal_zero_padding))
class MPL115A2:
# From the section 3.1 table:
# address bits
# total sign frac dec.zero.pad
__REGISTER_PADC = _MPL115A2_Register(0x00, 10, 0, 0, 0)
__REGISTER_TADC = _MPL115A2_Register(0x02, 10, 0, 0, 0)
__REGISTER_A0 = _MPL115A2_Register(0x04, 16, 1, 3, 0)
__REGISTER_B1 = _MPL115A2_Register(0x06, 16, 1, 13, 0)
__REGISTER_B2 = _MPL115A2_Register(0x08, 16, 1, 14, 0)
__REGISTER_C12 = _MPL115A2_Register(0x0A, 14, 1, 13, 9)
def __init__(self, address=0x60, debug=False):
self.i2c = Adafruit_I2C(address)
# Read coefficients
self.a0 = self.__REGISTER_A0.read(self.i2c)
self.b1 = self.__REGISTER_B1.read(self.i2c)
self.b2 = self.__REGISTER_B2.read(self.i2c)
self.c12 = self.__REGISTER_C12.read(self.i2c)
def getPT(self):
"""Returns a tuple of (pressure, temperature) as measured by the sensor."""
# Instruct the sensor to begin data conversion.
self.i2c.write8(0x12, 0x00)
# Wait until conversion has finished. The datasheet says "3ms". We'll
# wait 5ms just to be sure. Please note the documentation about
# time.sleep(), though:
# http://docs.python.org/3.0/library/time.html#time.sleep
time.sleep(0.005)
# Read the raw values.
padc = self.__REGISTER_PADC.read(self.i2c)
tadc = self.__REGISTER_TADC.read(self.i2c)
# Calculate compensated pressure value, section 3.2 of the datasheet.
pcomp = self.a0 + (self.b1 + self.c12 * tadc) * padc + self.b2 * tadc
# Calculate final values. The formula for pressure is from section 3.2
# of the datasheet. The formula for temperature is basically magic:
# http://www.adafruit.com/forums/viewtopic.php?f=19&t=41347
pressure = pcomp * ((115.0 - 50.0) / 1023.0) + 50.0
temperature = (tadc - 498.0) / -5.35 + 25.0
return (pressure, temperature)
def getPressure(self):
return self.getPT()[0]
def getTemperature(self):
return self.getPT()[1]
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