air_quality_sensors.py

# coding: utf-8

# A combined poller / calibrator when reading data from the BME680 and
# SGP30 sensors with a raspberry pi.

import csv
import datetime
import os
import time

import adafruit_sgp30
import bme680
import board
import busio


DATA_FILE = 'data-2.csv'
POLLING_INTERVAL = 20
DEBUG = False


def absolute_humidity(temperature, humidity):
    """Taken from a BME280 library (see below). This ignores the pressure
    but should be accurate enough.

    https://github.com/finitespace/BME280/blob/7a211f03aa3ac5567b14e2cbc12ac21e185b6e0b/src/EnvironmentCalculations.cpp#L65

    """

    mw = 18.01534  # molar mass of water g/mol
    r = 8.31447215  # Universal gas constant J/mol/K
    temp = pow(2.718281828, (17.67 * temperature) / (temperature + 243.5))
    return (6.112 * temp * humidity * mw) / ((273.15 + temperature) * r)


# SGP30

i2c = busio.I2C(board.SCL, board.SDA, frequency=100000)

# Create library object on our I2C port
sgp30 = adafruit_sgp30.Adafruit_SGP30(i2c)

print("SGP30 serial #", [hex(i) for i in sgp30.serial])

sgp30.iaq_init()

# TODO: Set baseline
# sgp30.set_iaq_baseline(0x8973, 0x8aae)


# BME680

try:
    sensor = bme680.BME680(bme680.I2C_ADDR_PRIMARY)
except IOError:
    sensor = bme680.BME680(bme680.I2C_ADDR_SECONDARY)

# These calibration data can safely be commented
# out, if desired.

print('Calibration data:')
for name in dir(sensor.calibration_data):

    if not name.startswith('_'):
        value = getattr(sensor.calibration_data, name)

        if isinstance(value, int):
            print('{}: {}'.format(name, value))

# These oversampling settings can be tweaked to
# change the balance between accuracy and noise in
# the data.

sensor.set_humidity_oversample(bme680.OS_2X)
sensor.set_pressure_oversample(bme680.OS_4X)
sensor.set_temperature_oversample(bme680.OS_8X)
sensor.set_filter(bme680.FILTER_SIZE_3)
sensor.set_gas_status(bme680.ENABLE_GAS_MEAS)

print('\n\nInitial reading:')
for name in dir(sensor.data):
    value = getattr(sensor.data, name)

    if not name.startswith('_'):
        print('{}: {}'.format(name, value))

sensor.set_gas_heater_temperature(320)
sensor.set_gas_heater_duration(150)
sensor.select_gas_heater_profile(0)

# Up to 10 heater profiles can be configured, each
# with their own temperature and duration.
# sensor.set_gas_heater_profile(200, 150, nb_profile=1)
# sensor.select_gas_heater_profile(1)

fieldnames = ['Datetime', 'Temperature', 'Pressure', 'Humidity',
              'eCO2', 'TVOC', 'Gas Resistance', 'Baseline eCO2',
              'Baseline TVOC']

if not os.path.isfile(DATA_FILE):
    with open(DATA_FILE, 'w', newline='') as f:
        writer = csv.DictWriter(f, fieldnames=fieldnames)
        writer.writeheader()

print('\n\nPolling:')

try:
    while True:
        # print("**** Baseline values: eCO2 = 0x%x, TVOC = 0x%x"
        #       % (sgp30.baseline_eCO2, sgp30.baseline_TVOC))
        if sensor.get_sensor_data():
            with open(DATA_FILE, 'a', newline='') as f:
                temperature = sensor.data.temperature
                humidity = sensor.data.humidity
                entry = {
                    'Datetime': datetime.datetime.now(),
                    'Temperature': temperature,
                    'Pressure': sensor.data.pressure,
                    'Humidity': humidity,
                    'eCO2': sgp30.eCO2,
                    'TVOC': sgp30.TVOC,
                    'Gas Resistance': sensor.data.gas_resistance,
                    'Baseline eCO2': sgp30.baseline_eCO2,
                    'Baseline TVOC': sgp30.baseline_TVOC,
                }

                if DEBUG:
                    print(entry)


                # Update humidity compensation on the SGP30
                sgp30.set_iaq_humidity(
                    gramsPM3=absolute_humidity(
                        humidity=humidity,
                        temperature=temperature,
                    ),
                )

                if not DEBUG:
                    writer = csv.DictWriter(f, fieldnames=fieldnames)
                    writer.writerow(entry)

        time.sleep(POLLING_INTERVAL)

except KeyboardInterrupt:
    pass