Source code for adafruit_sgp30

# SPDX-FileCopyrightText: 2017 ladyada for Adafruit Industries
#
# SPDX-License-Identifier: MIT

"""
`adafruit_sgp30`
====================================================

I2C driver for SGP30 Sensirion VoC sensor

* Author(s): ladyada

Implementation Notes
--------------------

**Hardware:**

* Adafruit `SGP30 Air Quality Sensor Breakout - VOC and eCO2
  <https://www.adafruit.com/product/3709>`_ (Product ID: 3709)

**Software and Dependencies:**

* Adafruit CircuitPython firmware for the supported boards:
  https://github.com/adafruit/circuitpython/releases
* Adafruit's Bus Device library: https://github.com/adafruit/Adafruit_CircuitPython_BusDevice
"""
import time
from math import exp
from adafruit_bus_device.i2c_device import I2CDevice
from micropython import const

__version__ = "0.0.0-auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_SGP30.git"


_SGP30_DEFAULT_I2C_ADDR = const(0x58)
_SGP30_FEATURESETS = (0x0020, 0x0022)

_SGP30_CRC8_POLYNOMIAL = const(0x31)
_SGP30_CRC8_INIT = const(0xFF)
_SGP30_WORD_LEN = const(2)


[docs]class Adafruit_SGP30: """ A driver for the SGP30 gas sensor. :param ~busio.I2C i2c: The I2C bus the SGP30 is connected to. :param int address: The I2C address of the device. Defaults to :const:`0x58` **Quickstart: Importing and using the SGP30 temperature sensor** Here is one way of importing the `Adafruit_SGP30` class so you can use it with the name ``sgp30``. First you will need to import the libraries to use the sensor .. code-block:: python import busio import board import adafruit_sgp30 Once this is done you can define your `busio.I2C` object and define your sensor object .. code-block:: python i2c = busio.I2C(board.SCL, board.SDA, frequency=100000) sgp30 = adafruit_sgp30.Adafruit_SGP30(i2c) Now you have access to the Carbon Dioxide Equivalent baseline using the :attr:`baseline_eCO2` attribute and the Total Volatile Organic Compound baseline using the :attr:`baseline_TVOC` .. code-block:: python eCO2 = sgp30.baseline_eCO2 TVOC = sgp30.baseline_TVOC """ def __init__(self, i2c, address=_SGP30_DEFAULT_I2C_ADDR): """Initialize the sensor, get the serial # and verify that we found a proper SGP30""" self._device = I2CDevice(i2c, address) # get unique serial, its 48 bits so we store in an array self.serial = self._i2c_read_words_from_cmd([0x36, 0x82], 0.01, 3) # get featureset featureset = self._i2c_read_words_from_cmd([0x20, 0x2F], 0.01, 1) if featureset[0] not in _SGP30_FEATURESETS: raise RuntimeError("SGP30 Not detected") self.iaq_init() @property # pylint: disable=invalid-name def TVOC(self): """Total Volatile Organic Compound in parts per billion.""" return self.iaq_measure()[1] @property # pylint: disable=invalid-name def baseline_TVOC(self): """Total Volatile Organic Compound baseline value""" return self.get_iaq_baseline()[1] @property # pylint: disable=invalid-name def eCO2(self): """Carbon Dioxide Equivalent in parts per million""" return self.iaq_measure()[0] @property # pylint: disable=invalid-name def baseline_eCO2(self): """Carbon Dioxide Equivalent baseline value""" return self.get_iaq_baseline()[0] @property # pylint: disable=invalid-name def Ethanol(self): """Ethanol Raw Signal in ticks""" return self.raw_measure()[1] @property # pylint: disable=invalid-name def H2(self): """H2 Raw Signal in ticks""" return self.raw_measure()[0]
[docs] def iaq_init(self): """Initialize the IAQ algorithm""" # name, command, signals, delay self._run_profile(["iaq_init", [0x20, 0x03], 0, 0.01])
[docs] def iaq_measure(self): """Measure the eCO2 and TVOC""" # name, command, signals, delay return self._run_profile(["iaq_measure", [0x20, 0x08], 2, 0.05])
[docs] def raw_measure(self): """Measure H2 and Ethanol (Raw Signals)""" # name, command, signals, delay return self._run_profile(["raw_measure", [0x20, 0x50], 2, 0.025])
[docs] def get_iaq_baseline(self): """Retreive the IAQ algorithm baseline for eCO2 and TVOC""" # name, command, signals, delay return self._run_profile(["iaq_get_baseline", [0x20, 0x15], 2, 0.01])
[docs] def set_iaq_baseline(self, eCO2, TVOC): # pylint: disable=invalid-name """Set the previously recorded IAQ algorithm baseline for eCO2 and TVOC""" if eCO2 == 0 and TVOC == 0: raise RuntimeError("Invalid baseline") buffer = [] for value in [TVOC, eCO2]: arr = [value >> 8, value & 0xFF] arr.append(self._generate_crc(arr)) buffer += arr self._run_profile(["iaq_set_baseline", [0x20, 0x1E] + buffer, 0, 0.01])
[docs] def set_iaq_humidity(self, gramsPM3): # pylint: disable=invalid-name """Set the humidity in g/m3 for eCO2 and TVOC compensation algorithm""" tmp = int(gramsPM3 * 256) buffer = [] for value in [tmp]: arr = [value >> 8, value & 0xFF] arr.append(self._generate_crc(arr)) buffer += arr self._run_profile(["iaq_set_humidity", [0x20, 0x61] + buffer, 0, 0.01])
[docs] def set_iaq_relative_humidity(self, celsius, relative_humidity): """ Set the humidity in g/m3 for eCo2 and TVOC compensation algorithm. The absolute humidity is calculated from the temperature (Celsius) and relative humidity (as a percentage). """ numerator = ((relative_humidity / 100) * 6.112) * exp( (17.62 * celsius) / (243.12 + celsius) ) denominator = 273.15 + celsius humidity_grams_pm3 = 216.7 * (numerator / denominator) self.set_iaq_humidity(humidity_grams_pm3)
# Low level command functions def _run_profile(self, profile): """Run an SGP 'profile' which is a named command set""" # pylint: disable=unused-variable name, command, signals, delay = profile # pylint: enable=unused-variable # print("\trunning profile: %s, command %s, %d, delay %0.02f" % # (name, ["0x%02x" % i for i in command], signals, delay)) return self._i2c_read_words_from_cmd(command, delay, signals) def _i2c_read_words_from_cmd(self, command, delay, reply_size): """Run an SGP command query, get a reply and CRC results if necessary""" with self._device: self._device.write(bytes(command)) time.sleep(delay) if not reply_size: return None crc_result = bytearray(reply_size * (_SGP30_WORD_LEN + 1)) self._device.readinto(crc_result) # print("\tRaw Read: ", crc_result) result = [] for i in range(reply_size): word = [crc_result[3 * i], crc_result[3 * i + 1]] crc = crc_result[3 * i + 2] if self._generate_crc(word) != crc: raise RuntimeError("CRC Error") result.append(word[0] << 8 | word[1]) # print("\tOK Data: ", [hex(i) for i in result]) return result # pylint: disable=no-self-use def _generate_crc(self, data): """8-bit CRC algorithm for checking data""" crc = _SGP30_CRC8_INIT # calculates 8-Bit checksum with given polynomial for byte in data: crc ^= byte for _ in range(8): if crc & 0x80: crc = (crc << 1) ^ _SGP30_CRC8_POLYNOMIAL else: crc <<= 1 return crc & 0xFF