bme680 air quality index

octoprint_enclosure/BME680_AQI.py

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+import bme680
+import time
+
+
+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.
+
+
+# These oversampling settings can be tweaked to
+# change the balance between accuracy and noise in
+# the data.
+
+hum_weighting = float(0.25)   # so hum effect is 25% of the total air quality score
+gas_weighting = float(0.75)   # so gas effect is 75% of the total air quality score
+
+sensor.set_humidity_oversample(bme680.OS_2X)
+sensor.set_pressure_oversample(bme680.OS_2X)
+sensor.set_temperature_oversample(bme680.OS_2X)
+sensor.set_filter(bme680.FILTER_SIZE_3)
+
+sensor.set_gas_heater_temperature(320)
+sensor.set_gas_heater_duration(150)
+sensor.select_gas_heater_profile(0)
+sensor.set_gas_status(bme680.ENABLE_GAS_MEAS)
+
+gas_reference = float(250000)
+hum_reference = float(40)
+getgasreference_count = int(0)
+
+
+def GetGasReference(gas_reference):
+  # Now run the sensor for a burn-in period, then use combination of relative humidity and gas resistance to estimate indoor air quality as a percentage.
+  # print("Getting a new gas reference value")
+  readings = int(10)
+  while True:
+    sensor.get_sensor_data()
+    if sensor.data.heat_stable:
+      for i in range(1, readings):  # // read gas for 10 x 0.150mS = 1.5secs
+        sensor.get_sensor_data()
+        gas_reference = gas_reference + sensor.data.gas_resistance
+        # print(sensor.data.gas_resistance)
+      gas_reference = gas_reference / readings
+      return
+
+
+
+
+  # for i in range(1, readings):  # // read gas for 10 x 0.150mS = 1.5secs
+  #   gas_reference = gas_reference + sensor.data.gas_resistance
+  #   print(sensor.data.gas_resistance)
+  # gas_reference = gas_reference / readings
+
+
+def CalculateIAQ(score):
+  IAQ_text = "Air quality is "
+  score = float((100 - score) * 5)
+  if score >= 301:
+    IAQ_text = IAQ_text + "Hazardous"
+  elif score >= 201 and score <= 300:
+    IAQ_text = IAQ_text + "Very Unhealthy"
+  elif score >= 176 and score <= 200:
+    IAQ_text = IAQ_text + "Unhealthy"
+  elif score >= 151 and score <= 175:
+    IAQ_text = IAQ_text + "Unhealthy for Sensitive Groups"
+  elif score >= 51 and score <= 150:
+    IAQ_text = IAQ_text + "Moderate"
+  elif score >= 00 and score <= 50:
+    IAQ_text = IAQ_text + "Good"
+  return IAQ_text
+
+
+
+#Calculate humidity contribution to IAQ index
+current_humidity = float(sensor.data.humidity)
+if (current_humidity >= 38 and current_humidity <= 42):
+	hum_score = float(0.25*100)  # Humidity +/-5% around optimum 
+else:
+  #sub-optimal
+  if (current_humidity < 38):
+    hum_score = float(0.25/hum_reference*current_humidity*100)
+  else:
+    hum_score = ((-0.25/(100-hum_reference)*current_humidity)+0.416666)*100
+
+
+#Calculate gas contribution to IAQ index
+gas_lower_limit = float(5000)   # Bad air quality limit
+gas_upper_limit = float(50000)  # Good air quality limit
+
+if (gas_reference > gas_upper_limit):  
+  gas_reference = gas_upper_limit   #gas_reference = 250000 see above
+if (gas_reference < gas_lower_limit): 
+  gas_reference = gas_lower_limit
+
+gas_score = float((0.75/(gas_upper_limit-gas_lower_limit)*gas_reference -(gas_lower_limit*(0.75/(gas_upper_limit-gas_lower_limit))))*100)
+
+# print('gas_upper_limit--------')
+# print(gas_upper_limit)
+#
+# print('gas_lower_limit--------')
+# print(gas_lower_limit)
+#
+#
+# print('gas score---------')
+# print(gas_score)
+#Combine results for the final IAQ index value (0-100% where 100% is good quality air)
+air_quality_score = float(hum_score + gas_score)
+
+# print('Air Quality = {0:.2f} % derived from 25% of Humidity reading and 75% of Gas reading - 100% is good quality air'.format( air_quality_score))
+
+# print('Humidity element was : {0:.2f} of 0.25'.format( hum_score/100))
+# print('     Gas element was : {0:.2f} of 0.25'.format( gas_score/100))
+
+
+
+
+# if (sensor.data.gas_resistance < 120000):
+# 	print('Poor air qulity *****')
+
+GetGasReference(gas_reference)
+
+# print(CalculateIAQ(air_quality_score))
+# print("------------------------------------------------")
+# time.sleep(2)
+print('{0:0.1f}'.format(air_quality_score))
+