#define RLOAD 2.0                 //parameters of sensor calibration
#define RZERO 546
#define PARA 116.6020682
#define PARB 2.769034857

#define ledRED  9                 // blue, yellow and red Leds
#define ledBLUE  8
#define ledYELLOW  7

int val = 0;
#include <SoftwareSerial.h>

int rx=4;                         // pins used to send data
int tx=6;

SoftwareSerial bluetoothSerial(rx,tx);

int ppm = 0;

void setup() {

  bluetoothSerial.begin(9600);    // begin serial
  pinMode(rx,INPUT);
  pinMode(tx,OUTPUT);
  
  //leds as outputs
  pinMode(ledBLUE, OUTPUT);       // leds as outputs
  pinMode(ledYELLOW, OUTPUT);
  pinMode(ledRED, OUTPUT);
}

void loop()
{
  val = analogRead(2);            // Read sensor analog pin 2
  
  //ppm=val;                      // due to lack of memory the analog imput 
                                  // can be sent and the math done in the APP!
  
  float val2 = (1023 / val * 5 - 1) * RLOAD;     //some math
  ppm = PARA * (val2 / RZERO) * (val2 / RZERO);  // Value in ppm

  if (ppm < 750) {                               // Blue led on
    digitalWrite(ledBLUE, HIGH);
    digitalWrite(ledYELLOW, LOW);
    digitalWrite(ledRED, LOW);
  }
  if (ppm >= 751 && ppm < 1300) {                //Yellow led on
    digitalWrite(ledBLUE, LOW);
    digitalWrite(ledYELLOW, HIGH);
    digitalWrite(ledRED, LOW);
  }
  if (ppm >= 1301) {                             // Red led on
    digitalWrite(ledBLUE, LOW);
    digitalWrite(ledYELLOW, LOW);
    digitalWrite(ledRED, HIGH);
  }

  bluetoothSerial.print(ppm);                   // print value
  delay(400);                                   // wait 400 ms
}