Breathalyzer using Alcohol Gas Sensor with Arduino

Arduino Based Breathalyzer

#define qtyLED 6  //Declare the quantity of LED's for the bar graph
int LEDs[qtyLED]; //Array to store the states of the LEDs
int sensorPin = 0; //Variable that will hold the current value of the sensor
int time; //Variable that will hold the amount of time for the sensor to be read
int maxreading; //Variable to store the maximum value read during the last reading
//For loop counting variables
int i;
int j;
 
void setup()
{ 
  //Initialize the counting variables
  //Serial.begin(9600);
  i=0;
  j=2;
  
  while(i < qtyLED) //While i is less than the number of defined LED's
  {                 //...save the value of i+2 in the LEDs array. we add 2 so that it represents one of our digital pins
    LEDs[i] = j;
    i++;
    j++;
  }
  
  for(i=0;i<qtyLED;i++) //Define the LED Pins as outputs. In this case 2->7
  {
    pinMode(LEDs[i], OUTPUT);
  }
  pinMode(13, OUTPUT); //Define pin 13 as an output so we can show when we are not taking a reading from the sensor(Blinkin
                       //...Or when we are taking a reading from the sensor (Solid)
}

void loop()
{
  PORTB = PORTB ^ 100000;  //Invert pin 13 to give the LED a blinking effect
  delay(100); //Delay so that the user can see the blinking happen
  int sensor = analogRead(sensorPin); //Read the sensors value and store it in the sensor variable
  if(sensor >= 40) //If the value is less that 40(value for the chemical being used in this example)
  {  
    digitalWrite(13, HIGH); //Turn on the blue LED indecating that the sensor detected a minimal amount of alcohol (sensor >= 40)
    maxreading = 0;         //Initiate the max reading to 0
    for(time = 0;time <= 5000;time++) //Read the sensor for 5 seconds
    {                                 //...every millisecond update the value of the max reading of the sensor
      int sensor = analogRead(sensorPin);
      delay(1);
      if(sensor > maxreading)
      {
        maxreading = sensor;
      }
    }
    digitalWrite(13, LOW); //As soon as the reading is complete turn off the blue LED
    int level = map(maxreading, 0, 200, 0, qtyLED); //Map the value from 0 to 200(reading from sensor) to 0 and the number of LEDs which is 6
                                                    //...0 to 6(LEDs) level determines how many of them turn on.
    for(i=0;i<qtyLED;i++) //Compare all the leds current state with the value of the level that was read
    {                     //if for example the level read was 5, then LEDs 2->6 would turn on.
      if (i < level) //If the current LED being checked is less that the level
      {
        digitalWrite(LEDs[i], HIGH); //...Turn it on
      }
      else //If the current LED being checked is higher than the level
      {
        digitalWrite(LEDs[i], LOW); //...Turn it off
      }
    }
    delay(10000); //Wait 10 seconds for the user to get the reading from the led bar graph
    for(i=0;i<qtyLED;i++) //Turn off all the LEDs
    {
      digitalWrite(LEDs[i],LOW);
    }
  }
}