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85 lines
2.8 KiB
Python
85 lines
2.8 KiB
Python
# refer to https://sensirion.com/media/documents/48C4B7FB/64C134E7/Sensirion_SCD4x_Datasheet.pdf
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import smbus3
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import struct
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import time
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from prometheus_client import start_http_server, Gauge
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import sys
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location = sys.argv[1]
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def sensiron_bad_crc8(data):
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crc = 0xFF
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POLY = 0x31
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for byte in data:
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crc ^= byte
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for _ in range(8):
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if crc & 0x80:
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crc = (crc << 1) ^ POLY
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else:
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crc = (crc << 1)
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crc &= 0xFF
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return crc
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bus = smbus3.SMBus(1)
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ADDR = 0x62
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def encode_word_crc(hi, lo):
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return [hi, lo, sensiron_bad_crc8([hi, lo])]
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def setup():
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stop_measurement = smbus3.i2c_msg.write(ADDR, [0x3f, 0x86])
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bus.i2c_rdwr(stop_measurement)
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time.sleep(0.5)
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serial_cmd = smbus3.i2c_msg.write(ADDR, [0x36, 0x82]) # serial number
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serial_read = smbus3.i2c_msg.read(ADDR, 9)
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bus.i2c_rdwr(serial_cmd, serial_read)
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serial = bytes(serial_read)
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print((serial[0:2] + serial[3:5] + serial[6:8]).hex())
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time.sleep(0.1)
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# automatic self-calibration breaks badly if CO2 never below 400ppm, which is not guaranteed
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disable_asc = smbus3.i2c_msg.write(ADDR, [0x24, 0x16] + encode_word_crc(0x00, 0x00))
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bus.i2c_rdwr(disable_asc)
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time.sleep(0.1)
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# default offset of 4 degrees C is "probably right" but I don't have the equipment to test this
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#real_offset = 4.0
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#offset_bytes = struct.pack(">H", int(real_offset * 65535.0 / 175.0))
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#set_temp_offset = smbus3.i2c_msg.write(ADDR, [0x24, 0x1d] + encode_word_crc(*offset_bytes))
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#bus.i2c_rdwr(set_temp_offset)
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#time.sleep(0.1)
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start_measurement = smbus3.i2c_msg.write(ADDR, [0x21, 0xb1])
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bus.i2c_rdwr(start_measurement)
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setup()
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temperature = Gauge("scd4x_temperature", "Temperature in Celsius", ("location",))
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co2_ppm = Gauge("scd4x_co2_ppm", "CO2 parts per million", ("location",))
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rh = Gauge("scd4x_relative_humidity_percent", "Relative humidity in percent", ("location",))
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def read_temperature_pressure():
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measurement_read_write = smbus3.i2c_msg.write(ADDR, [0xec, 0x05])
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measurement_read_read = smbus3.i2c_msg.read(ADDR, 9)
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bus.i2c_rdwr(measurement_read_write, measurement_read_read)
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measurement_read_read = bytes(measurement_read_read)
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print(measurement_read_read)
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co2 = struct.unpack(">H", measurement_read_read[0:2])[0]
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raw_temperature = struct.unpack(">H", measurement_read_read[3:5])[0]
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raw_humidity = struct.unpack(">H", measurement_read_read[6:8])[0]
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temperature_celsius = -45 + 175 * (raw_temperature / 65535.0)
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relative_humidity = raw_humidity / 65535.0 * 100
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temperature.labels(location=location).set(temperature_celsius)
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rh.labels(location=location).set(relative_humidity)
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co2_ppm.labels(location=location).set(co2)
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start_http_server(9091)
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while True:
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time.sleep(5)
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read_temperature_pressure() |