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baroClass.py
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# The MIT License (MIT)
#
# Copyright (c) 2017 Tony DiCola for Adafruit Industries
#
# 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.
"""
`adafruit_mpl3115a2`
====================================================
CircuitPython module for the MPL3115A2 barometric pressure & temperature sensor.
See examples/simpletest.py for a demo of the usage.
* Author(s): Tony DiCola
"""
import time
from micropython import const
try:
import ustruct as struct
except ImportError:
import struct
import adafruit_bus_device.i2c_device as i2c_device
__version__ = "0.0.0-auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_MPL3115A2.git"
#pylint: disable=bad-whitespace
# Internal constants:
_MPL3115A2_ADDRESS = const(0x60)
_MPL3115A2_REGISTER_STATUS = const(0x00)
_MPL3115A2_REGISTER_PRESSURE_MSB = const(0x01)
_MPL3115A2_REGISTER_PRESSURE_CSB = const(0x02)
_MPL3115A2_REGISTER_PRESSURE_LSB = const(0x03)
_MPL3115A2_REGISTER_TEMP_MSB = const(0x04)
_MPL3115A2_REGISTER_TEMP_LSB = const(0x05)
_MPL3115A2_REGISTER_DR_STATUS = const(0x06)
_MPL3115A2_OUT_P_DELTA_MSB = const(0x07)
_MPL3115A2_OUT_P_DELTA_CSB = const(0x08)
_MPL3115A2_OUT_P_DELTA_LSB = const(0x09)
_MPL3115A2_OUT_T_DELTA_MSB = const(0x0A)
_MPL3115A2_OUT_T_DELTA_LSB = const(0x0B)
_MPL3115A2_WHOAMI = const(0x0C)
_MPL3115A2_BAR_IN_MSB = const(0x14)
_MPL3115A2_BAR_IN_LSB = const(0x15)
_MPL3115A2_REGISTER_STATUS_TDR = const(0x02)
_MPL3115A2_REGISTER_STATUS_PDR = const(0x04)
_MPL3115A2_REGISTER_STATUS_PTDR = const(0x08)
_MPL3115A2_PT_DATA_CFG = const(0x13)
_MPL3115A2_PT_DATA_CFG_TDEFE = const(0x01)
_MPL3115A2_PT_DATA_CFG_PDEFE = const(0x02)
_MPL3115A2_PT_DATA_CFG_DREM = const(0x04)
_MPL3115A2_CTRL_REG1 = const(0x26)
_MPL3115A2_CTRL_REG2 = const(0x27)
_MPL3115A2_CTRL_REG3 = const(0x28)
_MPL3115A2_CTRL_REG4 = const(0x29)
_MPL3115A2_CTRL_REG5 = const(0x2A)
_MPL3115A2_CTRL_REG1_SBYB = const(0x01)
_MPL3115A2_CTRL_REG1_OST = const(0x02)
_MPL3115A2_CTRL_REG1_RST = const(0x04)
_MPL3115A2_CTRL_REG1_RAW = const(0x40)
_MPL3115A2_CTRL_REG1_ALT = const(0x80)
_MPL3115A2_CTRL_REG1_BAR = const(0x00)
_MPL3115A2_CTRL_REG1_OS1 = const(0x00)
_MPL3115A2_CTRL_REG1_OS2 = const(0x08)
_MPL3115A2_CTRL_REG1_OS4 = const(0x10)
_MPL3115A2_CTRL_REG1_OS8 = const(0x18)
_MPL3115A2_CTRL_REG1_OS16 = const(0x20)
_MPL3115A2_CTRL_REG1_OS32 = const(0x28)
_MPL3115A2_CTRL_REG1_OS64 = const(0x30)
_MPL3115A2_CTRL_REG1_OS128 = const(0x38)
_MPL3115A2_REGISTER_STARTCONVERSION = const(0x12)
#pylint: enable=bad-whitespace
class MPL3115A2:
"""Instance of the MPL3115A2 sensor. Must specify the following parameters
when creating an instance of this device:
- i2c: The I2C bus connected to the sensor.
In addition you can specify the following optional keyword arguments:
- address: The I2C address of the device if it's different from the default.
"""
# Class level buffer to reduce memory usage and allocations.
# Note this is not thread safe by design!
_BUFFER = bytearray(4)
def __init__(self, i2c, *, address=_MPL3115A2_ADDRESS):
self._device = i2c_device.I2CDevice(i2c, address)
# Validate the chip ID.
if self._read_u8(_MPL3115A2_WHOAMI) != 0xC0:
raise RuntimeError('Failed to find MPL3115A2, check your wiring!')
# Reset. Note the chip immediately resets and won't send an I2C back
# so we need to catch the OSError and swallow it (otherwise this fails
# expecting an ACK that never comes).
try:
self._write_u8(_MPL3115A2_CTRL_REG1, _MPL3115A2_CTRL_REG1_RST)
except OSError:
pass
time.sleep(0.01)
# Poll for the reset to finish.
self._poll_reg1(_MPL3115A2_CTRL_REG1_RST)
# Configure the chip registers with default values.
self._ctrl_reg1 = _MPL3115A2_CTRL_REG1_OS128 | _MPL3115A2_CTRL_REG1_ALT
self._write_u8(_MPL3115A2_CTRL_REG1, self._ctrl_reg1)
self._write_u8(_MPL3115A2_PT_DATA_CFG, _MPL3115A2_PT_DATA_CFG_TDEFE | \
_MPL3115A2_PT_DATA_CFG_PDEFE | \
_MPL3115A2_PT_DATA_CFG_DREM)
def _read_into(self, address, buf, count=None):
# Read bytes from the specified 8-bit address into the provided buffer.
# If the count is not specified then the entire buffer is filled,
# otherwise count bytes are copied in.
if count is None:
count = len(buf)
with self._device as i2c:
buf[0] = address & 0xFF
i2c.write(buf, end=1, stop=False)
i2c.readinto(buf, end=count)
def _read_u8(self, address):
# Read an 8-bit unsigned value from the specified 8-bit address.
self._read_into(address, self._BUFFER, count=1)
return self._BUFFER[0]
def _write_u8(self, address, val):
# Write an 8-bit unsigned value to the specified 8-bit address.
with self._device as i2c:
self._BUFFER[0] = address & 0xFF
self._BUFFER[1] = val & 0xFF
i2c.write(self._BUFFER, end=2)
def _write_u16_be(self, address, val):
# Write a 16-bit big endian unsigned value to the specified 8-bit
# address.
with self._device as i2c:
self._BUFFER[0] = address & 0xFF
self._BUFFER[1] = (val >> 8) & 0xFF
self._BUFFER[2] = val & 0xFF
i2c.write(self._BUFFER, end=3)
def _poll_reg1(self, mask):
# Poll the CTRL REG1 value for the specified masked bits to NOT be
# present.
while self._read_u8(_MPL3115A2_CTRL_REG1) & mask > 0:
time.sleep(0.01)
@property
def pressure(self):
"""Read the barometric pressure detected by the sensor in Pascals."""
# First poll for a measurement to be finished.
self._poll_reg1(_MPL3115A2_CTRL_REG1_OST)
# Set control bits for pressure reading.
self._ctrl_reg1 &= ~0b10000000 # Turn off bit 7, ALT.
self._write_u8(_MPL3115A2_CTRL_REG1, self._ctrl_reg1)
self._ctrl_reg1 |= 0b00000010 # Set OST to 1 to start measurement.
self._write_u8(_MPL3115A2_CTRL_REG1, self._ctrl_reg1)
# Poll status for PDR to be set.
while self._read_u8(_MPL3115A2_REGISTER_STATUS) & _MPL3115A2_REGISTER_STATUS_PDR == 0:
time.sleep(0.01)
# Read 3 bytes of pressure data into buffer.
self._read_into(_MPL3115A2_REGISTER_PRESSURE_MSB, self._BUFFER, count=3)
# Reconstruct 20-bit pressure value.
pressure = ((self._BUFFER[0] << 16) | \
(self._BUFFER[1] << 8) | \
self._BUFFER[2]) & 0xFFFFFF
pressure >>= 4
# Scale down to pascals.
return pressure / 4.0
@property
def altitude(self):
"""Read the altitude as calculated based on the sensor pressure and
previously configured pressure at sea-level. This will return a
value in meters. Set the sea-level pressure by updating the
sealevel_pressure property first to get a more accurate altitude value.
"""
# First poll for a measurement to be finished.
self._poll_reg1(_MPL3115A2_CTRL_REG1_OST)
# Set control bits for pressure reading.
self._ctrl_reg1 |= 0b10000000 # Turn on bit 0, ALT.
self._write_u8(_MPL3115A2_CTRL_REG1, self._ctrl_reg1)
self._ctrl_reg1 |= 0b00000010 # Set OST to 1 to start measurement.
self._write_u8(_MPL3115A2_CTRL_REG1, self._ctrl_reg1)
# Poll status for PDR to be set.
while self._read_u8(_MPL3115A2_REGISTER_STATUS) & _MPL3115A2_REGISTER_STATUS_PDR == 0:
time.sleep(0.01)
# Read 3 bytes of altitude data into buffer.
# Yes even though this is the address of the pressure register it
# returns altitude when the ALT bit is set above.
self._read_into(_MPL3115A2_REGISTER_PRESSURE_MSB, self._BUFFER, count=3)
# Reconstruct signed 32-bit altitude value (actually 24 bits shifted up
# and then scaled down).
self._BUFFER[3] = 0 # Top 3 bytes of buffer were read from the chip.
altitude = struct.unpack('>i', self._BUFFER[0:4])[0]
# Scale down to meters.
return altitude / 65535.0
@property
def temperature(self):
"""Read the temperature as measured by the sensor in degrees Celsius.
"""
# Poll status for TDR to be set.
while self._read_u8(_MPL3115A2_REGISTER_STATUS) & _MPL3115A2_REGISTER_STATUS_TDR == 0:
time.sleep(0.01)
# Read 2 bytes of data from temp register.
self._read_into(_MPL3115A2_REGISTER_TEMP_MSB, self._BUFFER, count=2)
# Reconstruct signed 12-bit value.
temperature = struct.unpack('>h', self._BUFFER[0:2])[0]
temperature >>= 4
# Scale down to degrees Celsius.
return temperature / 16.0
@property
def sealevel_pressure(self):
"""Read and write the pressure at sea-level used to calculate altitude.
You must look this up from a local weather or meteorlogical report for
the best accuracy. This is a value in Pascals.
"""
# Read the sea level pressure in bars.
self._read_into(_MPL3115A2_BAR_IN_MSB, self._BUFFER, count=2)
# Reconstruct 16-bit value and scale back to pascals.
pressure = (self._BUFFER[0] << 8) | self._BUFFER[1]
return pressure * 2.0
@sealevel_pressure.setter
def sealevel_pressure(self, val):
# Convert to bars of pressure and write to the sealevel register.
bars = val // 2
self._write_u16_be(_MPL3115A2_BAR_IN_MSB, bars)