Rough PM 2.5 Rework of code with AQI Calculation for use in displaying lights.

mp2.5.c

#include "Adafruit_PM25AQI.h"

Adafruit_PM25AQI aqi = Adafruit_PM25AQI();

int redLed=9;
int yellowLed=10;
int greenLed=11;

float LOWER_BOUND=100.00;
float UPPER_BOUND=151.00;
float DANGER=UPPER_BOUND*2.0;

void blinkLights() {
  digitalWrite(greenLed, HIGH);
  digitalWrite(yellowLed, HIGH);
  digitalWrite(redLed, HIGH);
  delay(250);
  digitalWrite(greenLed, LOW);
  digitalWrite(yellowLed, LOW);
  digitalWrite(redLed, LOW);
  delay(250);
}

// https://forum.airnowtech.org/t/aqi-calculations-overview-ozone-pm2-5-and-pm10/168
// https://forum.airnowtech.org/t/the-aqi-equation/169
float chart[6][4] = {
 {0.0, 12.0, 0.0, 50},
 {12.1, 35.4, 51, 100},
 {35.5, 55.4, 101, 150},
 {55.5,150.4, 151, 200},
 {150.5, 250.4, 201, 300},
 {250.5, 500.4, 301, 500}
};


float calculateAQI(float concentration) {
  int use = 6;
  
  for (int i = 0; i < 6; i++) {
    if (concentration >= chart[i][0] && concentration <= chart[i][1]) {
      use = i;
    }
  }

  return (chart[use][3]-chart[use][2])/(chart[use][1]-chart[use][0])*(concentration-chart[use][0])+chart[use][2];
}

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  while (!Serial) delay(10);

  Serial.println("Adafruit PMSA003I Air Quality Sensor");

  delay(1000);

  if (! aqi.begin_I2C()) {
    Serial.println("Could not find PM 2.5 sensor!");
    while (1) delay(10);
  }

  Serial.println("PM25 found!");

  pinMode(redLed, OUTPUT);
  digitalWrite(redLed, HIGH);
  pinMode(yellowLed, OUTPUT);
  digitalWrite(yellowLed, HIGH);
  pinMode(greenLed, OUTPUT);
  digitalWrite(greenLed, HIGH);

  blinkLights();
  blinkLights();
  blinkLights();
}

void loop() {
  // put your main code here, to run repeatedly:
  PM25_AQI_Data data;
  
  if (! aqi.read(&data)) {
    Serial.println("Could not read from AQI");
    delay(500);  // try again in a bit!
    return;
  }
  Serial.println(data.pm25_standard);

  float aqi_calculated = calculateAQI(data.pm25_standard);

  Serial.println(aqi_calculated);
  
  if (aqi_calculated <= LOWER_BOUND) {
    Serial.println("Green"); 
    digitalWrite(greenLed, HIGH);
    digitalWrite(yellowLed, LOW);
    digitalWrite(redLed, LOW);
  } else if ( aqi_calculated > LOWER_BOUND && aqi_calculated < UPPER_BOUND ) {
    Serial.println("Yellow"); 
    digitalWrite(yellowLed, HIGH);
    digitalWrite(greenLed, LOW);
    digitalWrite(redLed, LOW);
  } else if (aqi_calculated > UPPER_BOUND && aqi_calculated < DANGER) {
    Serial.println("Red"); 
    digitalWrite(redLed, HIGH);
    digitalWrite(yellowLed, LOW);
    digitalWrite(greenLed, LOW);
  } else if (aqi_calculated > DANGER) {
      blinkLights();
      blinkLights();
      blinkLights();
  }
  delay(1000);
}