added index algorithm

Author: AVanVlack

README.rst

@@ -1,23 +1,11 @@
 Introduction
 ============
 
-.. image:: https://readthedocs.org/projects/adafruit-circuitpython-sgp40/badge/?version=latest
-    :target: https://circuitpython.readthedocs.io/projects/sgp40/en/latest/
-    :alt: Documentation Status
+CircuitPython library for the Adafruit SGP40 Air Quality Sensor / VOC Index Sensor Breakouts. 
+This fork adds DFRobots VOC Index algorithm to adafruits CircuitPython library.
 
-.. image:: https://img.shields.io/discord/327254708534116352.svg
-    :target: https://adafru.it/discord
-    :alt: Discord
-
-.. image:: https://github.com/adafruit/Adafruit_CircuitPython_SGP40/workflows/Build%20CI/badge.svg
-    :target: https://github.com/adafruit/Adafruit_CircuitPython_SGP40/actions
-    :alt: Build Status
-
-.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
-    :target: https://github.com/psf/black
-    :alt: Code Style: Black
-
-CircuitPython library for the Adafruit SGP40 Air Quality Sensor / VOC Index Sensor Breakouts
+`Original Library <https://github.com/adafruit/Adafruit_CircuitPython_SGP40>`_
+`DFRobot Algorithm <https://github.com/DFRobot/DFRobot_SGP40>`_
 
 
 Dependencies
@@ -60,21 +48,7 @@ To install in a virtual environment in your current project:
 Usage Example
 =============
 
-.. code-block:: python3
-
-    import time
-    import board
-    import adafruit_sgp40
-
-    i2c = board.I2C()  # uses board.SCL and board.SDA
-    sgp = adafruit_sgp40(i2c)
-
-    while True:
-        print("Measurement: ", sgp.raw)
-        print("")
-        sleep(1)
-
-For humidity compensated raw gas readings, we'll need a secondary sensor such as the bme280
+For humidity compensated raw gas and voc index readings, we'll need a secondary sensor such as the bme280
 
 .. code-block:: python3
 
@@ -90,12 +64,20 @@ For humidity compensated raw gas readings, we'll need a secondary sensor such as
     while True:
         temperature = bme280.temperature
         humidity = bme280.relative_humidity
-        compensated_raw_gas = sgp.measure_raw(temperature = temperature, relative_humidity = humidity)
+
+        # Compensated raw gas reading
+        compensated_raw_gas = sgp.measure_index(temperature = temperature, relative_humidity = humidity)
+
+        # Compensated voc index reading
+        voc_index = sgp.measure_raw(temperature = temperature, relative_humidity = humidity)
+
         print(compensated_raw_gas)
+        print(voc_index)
         print("")
         time.sleep(1)
 
 
+It may take several minutes for the VOC index to start changing as it calibrates the baseline readings.
 
 Contributing
 ============

adafruit_sgp40.py

@@ -32,6 +32,7 @@
 from time import sleep
 from struct import unpack_from
 import adafruit_bus_device.i2c_device as i2c_device
+from voc_index_algorithm import DFRobot_VOCAlgorithm
 
 __version__ = "0.0.0-auto.0"
 __repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_SGP40.git"
@@ -118,6 +119,7 @@ def __init__(self, i2c, address=0x59):
         self.i2c_device = i2c_device.I2CDevice(i2c, address)
         self._command_buffer = bytearray(2)
         self._measure_command = _READ_CMD
+        self._voc_algorithm = DFRobot_VOCAlgorithm()
 
         self.initialize()
 
@@ -138,9 +140,10 @@ def initialize(self):
         featureset = self._read_word_from_command()
         if featureset[0] != 0x3220:
 
-            raise RuntimeError("Feature set does not match: %s" % hex(featureset[0]))
+            raise RuntimeError("Feature set does not match: %s" %
+                               hex(featureset[0]))
 
-        # VocAlgorithm_init(&voc_algorithm_params)
+        self._voc_algorithm.vocalgorithm_init()
 
         # Self Test
         self._command_buffer[0] = 0x28
@@ -232,6 +235,26 @@ def measure_raw(self, temperature=25, relative_humidity=50):
         self._measure_command = bytearray(_cmd)
         return self.raw
 
+    def measure_index(self, temperature=25, relative_humidity=50):
+        """ Measure VOC index after humidity compensation
+        :param float temperature: The temperature in degrees Celsius, defaults
+                                     to :const:`25`
+        :param float relative_humidity: The relative humidity in percentage, defaults
+                                     to :const:`50`
+        :note  VOC index can indicate the quality of the air directly. The larger the value, the worse the air quality.
+        :note    0-100,no need to ventilate, purify
+        :note    100-200,no need to ventilate, purify
+        :note    200-400,ventilate, purify
+        :note    00-500,ventilate, purify intensely
+        :return int The VOC index measured, ranged from 0 to 500
+        """
+        raw = self.measure_raw(temperature, relative_humidity)
+        if raw < 0:
+            return -1
+        else:
+            vocIndex = self._voc_algorithm.vocalgorithm_process(raw)
+            return vocIndex
+
     def _read_word_from_command(
         self,
         delay_ms=10,
@@ -264,9 +287,9 @@ def _read_word_from_command(
             i2c.readinto(replybuffer, end=replylen)
 
         for i in range(0, replylen, 3):
-            if not self._check_crc8(replybuffer[i : i + 2], replybuffer[i + 2]):
+            if not self._check_crc8(replybuffer[i: i + 2], replybuffer[i + 2]):
                 raise RuntimeError("CRC check failed while reading data")
-            readdata_buffer.append(unpack_from(">H", replybuffer[i : i + 2])[0])
+            readdata_buffer.append(unpack_from(">H", replybuffer[i: i + 2])[0])
 
         return readdata_buffer
 
@@ -294,7 +317,7 @@ def _generate_crc(crc_buffer):
                 if crc & 0x80:
                     crc = (
                         crc << 1
-                    ) ^ 0x31  #  0x31 is the Seed for SGP40's CRC polynomial
+                    ) ^ 0x31  # 0x31 is the Seed for SGP40's CRC polynomial
                 else:
                     crc = crc << 1
         return crc & 0xFF  # Returns only bottom 8 bits

examples/sgp40_indextest.py

@@ -0,0 +1,23 @@
+import time
+import board
+import adafruit_sgp40
+import adafruit_bme280
+
+# Boards i2c bus
+i2c = board.I2C()  # uses board.SCL and board.SDA
+sgp = adafruit_sgp40.SGP40(i2c)
+
+# Humidity sensor for compensated Readings
+bme280 = adafruit_bme280.Adafruit_BME280_I2C(i2c)
+
+while True:
+    temperature = bme280.temperature
+    humidity = bme280.relative_humidity
+
+    # Compensated voc index reading
+    voc_index = sgp.measure_raw(
+        temperature=temperature, relative_humidity=humidity)
+
+    print(voc_index)
+    print("")
+    time.sleep(1)