Updated for Adafruit BME680 library changes

ESP32_bme680_CC_demo_03.ino

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+/*
+    Calculate IAQ indices scaled 0-100% (100% is excellent) and 0-500 where 0 is excellent and 500 Hazardous
+    The index is a hybrid of humidity and adverse gas content. See the Redme for further detaisl of the index.
+
+    This software, the ideas and concepts is Copyright (c) David Bird 2019. All rights to this software are reserved.
+
+    Any redistribution or reproduction of any part or all of the contents in any form is prohibited other than the following:
+    1. You may print or download to a local hard disk extracts for your personal and non-commercial use only.
+    2. You may copy the content to individual third parties for their personal use, but only if you acknowledge the author David Bird as the source of the material.
+    3. You may not, except with my express written permission, distribute or commercially exploit the content.
+    4. You may not transmit it or store it in any other website or other form of electronic retrieval system for commercial purposes.
+
+    The above copyright ('as annotated') notice and this permission notice shall be included in all copies or substantial portions of the Software and where the
+    software use is visible to an end-user.
+
+    THE SOFTWARE IS PROVIDED "AS IS" FOR PRIVATE USE ONLY, IT IS NOT FOR COMMERCIAL USE IN WHOLE OR PART OR CONCEPT. FOR PERSONAL USE IT IS SUPPLIED WITHOUT WARRANTY
+    OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+    IN NO EVENT SHALL THE AUTHOR OR COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+    See more at http://www.dsbird.org.uk
+*/
+/****************************************************************************
+  This is a library for the BME680 gas, humidity, temperature & pressure sensor
+  Designed specifically to work with the Adafruit BME680 Breakout
+  ----> http://www.adafruit.com/products/XXXX
+  These sensors use I2C or SPI to communicate, 2 or 4 pins are required
+  to interface.
+  Adafruit invests time and resources providing this open source code,
+  please support Adafruit andopen-source hardware by purchasing products
+  from Adafruit!
+  Written by Limor Fried & Kevin Townsend for Adafruit Industries.
+  BSD license, all text above must be included in any redistribution
+ ***************************************************************************/
+#include <Wire.h>
+#include <Adafruit_Sensor.h>
+#include "Adafruit_BME680.h"
+
+#define SEALEVELPRESSURE_HPA (1013.25)
+
+Adafruit_BME680 bme; // I2C
+
+float hum_weighting = 0.25; // so hum effect is 25% of the total air quality score
+float gas_weighting = 0.75; // so gas effect is 75% of the total air quality score
+
+int   humidity_score, gas_score;
+float gas_reference = 2500;
+float hum_reference = 40;
+int   getgasreference_count = 0;
+int   gas_lower_limit = 10000;  // Bad air quality limit
+int   gas_upper_limit = 300000; // Good air quality limit
+
+void setup() {
+  Serial.begin(115200);
+  Serial.println(F("BME680 test"));
+  Wire.begin();
+  if (!bme.begin()) {
+    Serial.println("Could not find a valid BME680 sensor, check wiring!");
+    while (1);
+  } else Serial.println("Found a sensor");
+
+  // Set up oversampling and filter initialization
+  bme.setTemperatureOversampling(BME680_OS_8X);
+  bme.setHumidityOversampling(BME680_OS_2X);
+  bme.setPressureOversampling(BME680_OS_4X);
+  bme.setIIRFilterSize(BME680_FILTER_SIZE_3);
+  bme.setGasHeater(320, 150); // 320°C for 150 ms
+  // Now run the sensor to normalise the readings, then use combination of relative humidity and gas resistance to estimate indoor air quality as a percentage.
+  // The sensor takes ~30-mins to fully stabilise
+  GetGasReference();
+}
+
+void loop() {
+  Serial.println("Sensor Readings:");
+  Serial.println("  Temperature = " + String(bme.readTemperature(), 2)     + "°C");
+  Serial.println("     Pressure = " + String(bme.readPressure() / 100.0F) + " hPa");
+  Serial.println("     Humidity = " + String(bme.readHumidity(), 1)        + "%");
+  Serial.println("          Gas = " + String(gas_reference)               + " ohms\n");
+  Serial.print("Qualitative Air Quality Index ");
+
+  humidity_score = GetHumidityScore();
+  gas_score      = GetGasScore();
+
+  //Combine results for the final IAQ index value (0-100% where 100% is good quality air)
+  float air_quality_score = humidity_score + gas_score;
+  Serial.println(" comprised of " + String(humidity_score) + "% Humidity and " + String(gas_score) + "% Gas");
+  if ((getgasreference_count++) % 5 == 0) GetGasReference();
+  Serial.println(CalculateIAQ(air_quality_score));
+  Serial.println("--------------------------------------------------------------");
+  delay(2000);
+}
+
+void GetGasReference() {
+  // 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.
+  //Serial.println("Getting a new gas reference value");
+  int readings = 10;
+  for (int i = 1; i <= readings; i++) { // read gas for 10 x 0.150mS = 1.5secs
+    gas_reference += bme.readGas();
+  }
+  gas_reference = gas_reference / readings;
+  //Serial.println("Gas Reference = "+String(gas_reference,3));
+}
+
+String CalculateIAQ(int score) {
+  String IAQ_text = "air quality is ";
+  score = (100 - score) * 5;
+  score = 175;
+  if      (score >= 301)                  IAQ_text += "Hazardous";
+  else if (score >= 201 && score <= 300 ) IAQ_text += "Very Unhealthy";
+  else if (score >= 176 && score <= 200 ) IAQ_text += "Unhealthy";
+  else if (score >= 151 && score <= 175 ) IAQ_text += "Unhealthy for Sensitive Groups";
+  else if (score >=  51 && score <= 150 ) IAQ_text += "Moderate";
+  else if (score >=  00 && score <=  50 ) IAQ_text += "Good";
+  Serial.print("IAQ Score = " + String(score) + ", ");
+  return IAQ_text;
+}
+
+int GetHumidityScore() {  //Calculate humidity contribution to IAQ index
+  float current_humidity = bme.readHumidity();
+  if (current_humidity >= 38 && current_humidity <= 42) // Humidity +/-5% around optimum
+    humidity_score = 0.25 * 100;
+  else
+  { // Humidity is sub-optimal
+    if (current_humidity < 38)
+      humidity_score = 0.25 / hum_reference * current_humidity * 100;
+    else
+    {
+      humidity_score = ((-0.25 / (100 - hum_reference) * current_humidity) + 0.416666) * 100;
+    }
+  }
+  return humidity_score;
+}
+
+int GetGasScore() {
+  //Calculate gas contribution to IAQ index
+  gas_score = (0.75 / (gas_upper_limit - gas_lower_limit) * gas_reference - (gas_lower_limit * (0.75 / (gas_upper_limit - gas_lower_limit)))) * 100.00;
+  if (gas_score > 75) gas_score = 75; // Sometimes gas readings can go outside of expected scale maximum
+  if (gas_score <  0) gas_score = 0;  // Sometimes gas readings can go outside of expected scale minimum
+  return gas_score;
+}