pressure_example_ulab.py

import time

import adafruit_bmp280
import board
import displayio
import ulab

# Blank the screen.  Scrolling text causes unwanted delays.
d = displayio.Group()
board.DISPLAY.show(d)

# Sampling rate: 16Hz
# Cutoff frequency: 0.16Hz
# Transition bandwidth: 0.16Hz
# Window type: Hamming
# Filter has 311 coefficients
taps = ulab.numpy.array([
    -0.000050679794726066, -0.000041099278318167, -0.000031279920668665,
    -0.000021183486597150, -0.000010770285292045, +0.000000000000000000,
    +0.000011167446754809, +0.000022770999889941, +0.000034847558259864,
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    +0.000438798585855176, +0.000415285995764155, +0.000387525565446236] +
    [+0.000355376044004699, +0.000318715033091691, +0.000277440901501588,
    +0.000231474653767861, +0.000180761739242710, +0.000125273788160487,
    +0.000065010261293197, +0.000000000000000000, -0.000069697336247377,
    -0.000143989957415198, -0.000222752767634882, -0.000305826338672358,
    -0.000393016043088374, -0.000484091357342654, -0.000578785344322494,
    -0.000676794323931742, -0.000777777739462615, -0.000881358226495441,
    -0.000987121890034750, -0.001094618794499868, -0.001203363670049808,
    -0.001312836837542114, -0.001422485353209744, -0.001531724372895900,
    -0.001639938734420840, -0.001746484755374530, -0.001850692242341569,
    -0.001951866706278179, -0.002049291777482158, -0.002142231812333790,
    -0.002229934682745978, -0.002311634738053158, -0.002386555927898205,
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    -0.002044504738458277, -0.001892680620886388, -0.001722455325210333,
    -0.001533548017297868, -0.001325738543930948, -0.001098869965763655,
    -0.000852850856865069, -0.000587657355512251, -0.000303334951952833,
    +0.000000000000000001, +0.000322159059450752, +0.000662880773589522,
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    +0.009793556645595150, +0.010343592108937170, +0.010891587022627668,
    +0.011436078436539264, +0.011975593032464911, +0.012508652552774892,
    +0.013033779302562583, +0.013549501700820601, +0.014054359855790191,
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    +0.017166546887869318, +0.017535153501103896, +0.017881182383493146] +
    [+0.018203584559716979, +0.018501378539810983, +0.018773654273367416,
    +0.019019576825867947, +0.019238389759765797, +0.019429418204303113,
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    +0.019950199166862841, +0.019905188596781104, +0.019830326636332028,
    +0.019725846101288819, +0.019592071599501125, +0.019429418204303113,
    +0.019238389759765800, +0.019019576825867947, +0.018773654273367420,
    +0.018501378539810983, +0.018203584559716979, +0.017881182383493149,
    +0.017535153501103892, +0.017166546887869318, +0.016776474791055797,
    +0.016366108277098043, +0.015936672560369614, +0.015489442135386881,
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    +0.007062587782654920, +0.006529795699742466, +0.006004483564265146,
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    -0.000587657355512251, -0.000852850856865070, -0.001098869965763655] +
    [-0.001325738543930948, -0.001533548017297868, -0.001722455325210333,
    -0.001892680620886389, -0.002044504738458278, -0.002178266442894981,
    -0.002294359479963247, -0.002393229444145818, -0.002475370483091317,
    -0.002541321857718479, -0.002591664377536210, -0.002627016731069256,
    -0.002648031731496151, -0.002655392497711923, -0.002649808591023195,
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    -0.002311634738053157, -0.002229934682745978, -0.002142231812333790,
    -0.002049291777482159, -0.001951866706278179, -0.001850692242341569,
    -0.001746484755374531, -0.001639938734420841, -0.001531724372895900,
    -0.001422485353209745, -0.001312836837542114, -0.001203363670049807,
    -0.001094618794499867, -0.000987121890034750, -0.000881358226495441,
    -0.000777777739462615, -0.000676794323931742, -0.000578785344322494,
    -0.000484091357342654, -0.000393016043088375, -0.000305826338672358,
    -0.000222752767634882, -0.000143989957415198, -0.000069697336247377,
    +0.000000000000000000, +0.000065010261293198, +0.000125273788160487,
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    +0.000377579817760223, +0.000358893160569588, +0.000339761667195315,
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    +0.000204671152403140, +0.000186449080596567, +0.000168714736477861,
    +0.000151511309510219, +0.000134870996840645, +0.000118815575023601,
    +0.000103357045109305, +0.000088498343199344, +0.000074234108254511,
    +0.000060551498686721, +0.000047431049079466, +0.000034847558259864,
    +0.000022770999889941, +0.000011167446754809, +0.000000000000000000,
    -0.000010770285292045, -0.000021183486597150, -0.000031279920668665,
    -0.000041099278318167, -0.000050679794726066,
])

# How often we are going to poll the sensor (If you change this, you need
# to change the filter above and the integration time below)
dt = 62500000 # 16Hz, 62.5ms

# Wait until after deadline_ns has passed
def sleep_deadline(deadline_ns):
    while time.monotonic_ns() < deadline_ns:
        pass


# Initialize our sensor
i2c = board.I2C()
sensor = adafruit_bmp280.Adafruit_BMP280_I2C(i2c)
sensor.standby_period = adafruit_bmp280.STANDBY_TC_1000
# Disable in-sensor filtering, because we want to show how it's done in
# CircuitPython
sensor.iir_filter = adafruit_bmp280.IIR_FILTER_DISABLE
sensor.overscan_pressure = adafruit_bmp280.OVERSCAN_X1

# And our data structures
# The most recent data samples, equal in number to the filter taps
data = ulab.numpy.zeros(len(taps))
t0 = deadline = time.monotonic_ns()
n = 0
# Take an initial reading to subtract off later, so that the graph in mu
# accentuates the small short term changes in pressure rather than the large
# DC offset of around 980
offset = sensor.pressure

while True:
    deadline += dt
    sleep_deadline(deadline)
    # Move the trace near the origin so small differences can be seen in the mu
    # plot window .. you wouldn't do this subtraction step if you are really
    # interested in absolute barometric pressure.
    value = sensor.pressure - offset
    if n == 0:
        # The first time, fill the filter with the initial value
        data = data + value
    else:
        # Otherwise, add it as the next sample
        ulab.numpy.roll(data, 1)
        data[-1] = value
    filtered = ulab.numpy.sum(data * taps)
    # Actually print every 10th value.  This prints about 1.6 values per
    # second.  You can print values more quickly by removing the 'if' and
    # making the print unconditional, or change the frequency of prints up
    # or down by changing the number '10'.
    if n % 10 == 0:
        print((filtered, value))
    n += 1