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208 lines
6.3 KiB
208 lines
6.3 KiB
3 years ago
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# Copyright (c) 2018-2020 Mika Tuupola
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#
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# Permission is hereby granted, free of charge, to any person obtaining a copy
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# of this software and associated documentation files (the "Software"), to
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# deal in the Software without restriction, including without limitation the
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# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
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# sell copied of the Software, and to permit persons to whom the Software is
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# furnished to do so, subject to the following conditions:
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#
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# The above copyright notice and this permission notice shall be included in
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# all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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# SOFTWARE.
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# https://github.com/tuupola/micropython-mpu9250
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# https://www.akm.com/akm/en/file/datasheet/AK8963C.pdf
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"""
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MicroPython I2C driver for AK8963 magnetometer
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"""
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__version__ = "0.3.0"
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# pylint: disable=import-error
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import ustruct
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import utime
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from machine import I2C, Pin
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from micropython import const
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# pylint: enable=import-error
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_WIA = const(0x00)
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_HXL = const(0x03)
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_HXH = const(0x04)
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_HYL = const(0x05)
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_HYH = const(0x06)
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_HZL = const(0x07)
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_HZH = const(0x08)
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_ST2 = const(0x09)
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_CNTL1 = const(0x0a)
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_ASAX = const(0x10)
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_ASAY = const(0x11)
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_ASAZ = const(0x12)
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_MODE_POWER_DOWN = 0b00000000
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MODE_SINGLE_MEASURE = 0b00000001
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MODE_CONTINOUS_MEASURE_1 = 0b00000010 # 8Hz
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MODE_CONTINOUS_MEASURE_2 = 0b00000110 # 100Hz
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MODE_EXTERNAL_TRIGGER_MEASURE = 0b00000100
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_MODE_SELF_TEST = 0b00001000
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_MODE_FUSE_ROM_ACCESS = 0b00001111
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OUTPUT_14_BIT = 0b00000000
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OUTPUT_16_BIT = 0b00010000
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_SO_14BIT = 0.6 # μT per digit when 14bit mode
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_SO_16BIT = 0.15 # μT per digit when 16bit mode
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class AK8963:
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"""Class which provides interface to AK8963 magnetometer."""
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def __init__(
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self, i2c, address=0x0c,
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mode=MODE_CONTINOUS_MEASURE_1, output=OUTPUT_16_BIT,
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offset=(0, 0, 0), scale=(1, 1, 1)
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):
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self.i2c = i2c
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self.address = address
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self._offset = offset
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self._scale = scale
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if 0x48 != self.whoami:
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raise RuntimeError("AK8963 not found in I2C bus.")
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# Sensitivity adjustement values
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self._register_char(_CNTL1, _MODE_FUSE_ROM_ACCESS)
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asax = self._register_char(_ASAX)
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asay = self._register_char(_ASAY)
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asaz = self._register_char(_ASAZ)
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self._register_char(_CNTL1, _MODE_POWER_DOWN)
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# Should wait atleast 100us before next mode
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self._adjustement = (
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(0.5 * (asax - 128)) / 128 + 1,
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(0.5 * (asay - 128)) / 128 + 1,
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(0.5 * (asaz - 128)) / 128 + 1
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)
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# Power on
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self._register_char(_CNTL1, (mode | output))
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if output is OUTPUT_16_BIT:
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self._so = _SO_16BIT
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else:
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self._so = _SO_14BIT
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@property
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def magnetic(self):
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"""
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X, Y, Z axis micro-Tesla (uT) as floats.
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"""
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xyz = list(self._register_three_shorts(_HXL))
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self._register_char(_ST2) # Enable updating readings again
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# Apply factory axial sensitivy adjustements
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xyz[0] *= self._adjustement[0]
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xyz[1] *= self._adjustement[1]
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xyz[2] *= self._adjustement[2]
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# Apply output scale determined in constructor
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so = self._so
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xyz[0] *= so
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xyz[1] *= so
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xyz[2] *= so
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# Apply hard iron ie. offset bias from calibration
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xyz[0] -= self._offset[0]
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xyz[1] -= self._offset[1]
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xyz[2] -= self._offset[2]
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# Apply soft iron ie. scale bias from calibration
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xyz[0] *= self._scale[0]
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xyz[1] *= self._scale[1]
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xyz[2] *= self._scale[2]
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return tuple(xyz)
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@property
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def adjustement(self):
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return self._adjustement
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@property
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def whoami(self):
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""" Value of the whoami register. """
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return self._register_char(_WIA)
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def calibrate(self, count=256, delay=200):
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self._offset = (0, 0, 0)
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self._scale = (1, 1, 1)
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reading = self.magnetic
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minx = maxx = reading[0]
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miny = maxy = reading[1]
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minz = maxz = reading[2]
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while count:
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utime.sleep_ms(delay)
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reading = self.magnetic
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minx = min(minx, reading[0])
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maxx = max(maxx, reading[0])
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miny = min(miny, reading[1])
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maxy = max(maxy, reading[1])
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minz = min(minz, reading[2])
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maxz = max(maxz, reading[2])
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count -= 1
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# Hard iron correction
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offset_x = (maxx + minx) / 2
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offset_y = (maxy + miny) / 2
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offset_z = (maxz + minz) / 2
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self._offset = (offset_x, offset_y, offset_z)
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# Soft iron correction
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avg_delta_x = (maxx - minx) / 2
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avg_delta_y = (maxy - miny) / 2
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avg_delta_z = (maxz - minz) / 2
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avg_delta = (avg_delta_x + avg_delta_y + avg_delta_z) / 3
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scale_x = avg_delta / avg_delta_x
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scale_y = avg_delta / avg_delta_y
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scale_z = avg_delta / avg_delta_z
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self._scale = (scale_x, scale_y, scale_z)
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return self._offset, self._scale
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def _register_short(self, register, value=None, buf=bytearray(2)):
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if value is None:
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self.i2c.readfrom_mem_into(self.address, register, buf)
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return ustruct.unpack("<h", buf)[0]
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ustruct.pack_into("<h", buf, 0, value)
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return self.i2c.writeto_mem(self.address, register, buf)
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def _register_three_shorts(self, register, buf=bytearray(6)):
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self.i2c.readfrom_mem_into(self.address, register, buf)
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return ustruct.unpack("<hhh", buf)
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def _register_char(self, register, value=None, buf=bytearray(1)):
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if value is None:
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self.i2c.readfrom_mem_into(self.address, register, buf)
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return buf[0]
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ustruct.pack_into("<b", buf, 0, value)
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return self.i2c.writeto_mem(self.address, register, buf)
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def __enter__(self):
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return self
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def __exit__(self, exception_type, exception_value, traceback):
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pass
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