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ms5837.py: add automatic sensor variant detection #26

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Merged
patrickelectric merged 1 commit into from
Jun 30, 2025
Merged

ms5837.py: add automatic sensor variant detection #26

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31 changes: 29 additions & 2 deletions ms5837/ms5837.py
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,12 @@
# Models
MODEL_02BA = 0
MODEL_30BA = 1
MODEL_UNKNOWN = 255

# context: https://github.com/ArduPilot/ardupilot/pull/29122#issuecomment-2877269114
MS5837_02BA_MAX_SENSITIVITY = 49000;
MS5837_02BA_30BA_SEPARATION = 37000;
MS5837_30BA_MIN_SENSITIVITY = 26000;

# Oversampling options
OSR_256 = 0
Expand Down Expand Up @@ -47,7 +53,7 @@ class MS5837(object):
_MS5837_CONVERT_D1_256 = 0x40
_MS5837_CONVERT_D2_256 = 0x50

def __init__(self, model=MODEL_30BA, bus=1):
def __init__(self, model=MODEL_UNKNOWN, bus=1):
self._model = model

try:
Expand Down Expand Up @@ -85,8 +91,27 @@ def init(self):
if crc != self._crc4(self._C):
print("PROM read error, CRC failed!")
return False

if self._model == MODEL_UNKNOWN:
self.auto_detect_model()

return True

def auto_detect_model(self):
""" Automatically detect sensor variant, with a heuristic threshold.

Details in https://github.com/ArduPilot/ardupilot/pull/29122#issuecomment-2877269114x

TODO: include detection of product version / package type, from PROM Word 0, per
https://github.com/ArduPilot/ardupilot/pull/29122#pullrequestreview-2837597764
"""
pressure_sensitivity = self._C[1]
if MS5837_30BA_MIN_SENSITIVITY <= pressure_sensitivity <= MS5837_02BA_30BA_SEPARATION:
self._model = MODEL_30BA
elif MS5837_02BA_30BA_SEPARATION < pressure_sensitivity <= MS5837_02BA_MAX_SENSITIVITY:
self._model = MODEL_02BA
else:
self._model = MODEL_UNKNOWN

def read(self, oversampling=OSR_8192):
if self._bus is None:
Expand Down Expand Up @@ -160,10 +185,12 @@ def _calculate(self):
SENS = self._C[1]*65536+(self._C[3]*dT)/128
OFF = self._C[2]*131072+(self._C[4]*dT)/64
self._pressure = (self._D1*SENS/(2097152)-OFF)/(32768)
else:
elif self._model == MODEL_30BA:
SENS = self._C[1]*32768+(self._C[3]*dT)/256
OFF = self._C[2]*65536+(self._C[4]*dT)/128
self._pressure = (self._D1*SENS/(2097152)-OFF)/(8192)
else:
raise NotImplementedError("Cannot calculate pressure for unknown model type!")

self._temperature = 2000+dT*self._C[6]/8388608

Expand Down