Indoor CO2 Sensor "kukO2" © GPL3+

// inlcude librqries needed:

#include <SoftwareSerial.h>
#include <Servo.h>

// Initiate Servo oject
Servo window_control;

// These constants won't change:
const int sensorPin = A0;    // pin that the sensor is attached to
const int LEDPIN = 9;        // pin that the LED is attached to
const int ZU = 10;            // Position of the servo motor for start (Zu)
const int AUF = 30;         // Position of the servo motor for end - position (a18uf)
const int BAD_AIR = 220;     // Default Wert empirisch ermittelt fr schlechte Luft
const int GOOD_AIR = 150;    // Default Wert empirisch ermittelt fr gute Luft
const int OPEN = 1;          // Define value for "OPEN" using the button
const int CLOSED = 0;        // Define value for "CLOSED" using the button
const int TASTE_IN = 7;      // define digital input channel to connect the button

// variables:
int window_pos = 0;          // Variable controlling the window position (open and closed)
float sensorValue = 0;       // the sensor value
float bad_air = BAD_AIR;     // Loaad limit value with default
float good_air = GOOD_AIR;   // Loaad limit value with default
int window_status = CLOSED;  // Variable storing window status (closed or open)

// ---------------------
// Setup routine:
// ---------------------

void setup() {
  // declare the Input nd output pins used on Arduino:
  pinMode(TASTE_IN, INPUT);  // sets the digital pin 7 as input
  pinMode(LEDPIN, OUTPUT);   // Set external LED control 
  window_control.attach(10); // declare usage of PWM pin "10" 
  Serial.begin(9600);        // initialize the debugging monitor for development purposes
  Window_close();            // Close window at start
  start_sensor();            // Sensor ein paar mal einlesen, bis er gute Werte erzeugt.
}

// --------------------- 
// endless main- loop:
// ---------------------
void loop() {
 
  digitalWrite(LEDPIN, HIGH);         // Light control LED
  Read_CO2_Sensor();                  // Read in the CO2 senor value
  Calibrate();                        // Set a new current "good value" to calibrate the mechanism
  Serial.println(sensorValue);        // send sensor value to debugging window
  if(sensorValue < good_air)          // In case current sensor value is better as worst "good air" limit
  {
    if(window_status != CLOSED)       // Check if window is not closed already
    {
      Window_close();                 // close the window
      window_status = CLOSED;         // remember it was closed
    }
  }
  else if (sensorValue > bad_air)     // Check if current sensor value is worse as allowed bad air limit 
  {
    if(window_status != OPEN)         // Check if window is open already
    {
      Window_open();                  // open the window
      window_status = OPEN;           // remember it was closed
    }  
  }
  digitalWrite(LEDPIN, LOW);          // Reset control LED
}

// ---------------------
// Supporting functions:
// ---------------------

// --------------------------------------------------------------------
// Function Checking for settinng new "good air limit"
// --------------------------------------------------------------------
void Calibrate(void)
{  
  int i;
  int taste;

  taste = digitalRead(TASTE_IN);
  //Serial.print(" Taste: ");       // for better redability in debug window
  //Serial.print(taste);            // send sensor value to debugging window 
  Serial.print("      Limit: ");
  Serial.print(abs(good_air));      // send current good air - limit to debug window
  Serial.print("      Limit: ");
  Serial.print(abs(bad_air));       // send current good air - limit to debug window
  Serial.print("      Act-Value: ");
  
  if(taste == 0) 
  {
 
    good_air = sensorValue;         // set the new good_air limit to the current value (after windos had been opened for a while)
    bad_air = good_air + 30;        // Set the jysteresis to 40PPM
    for(i=0;i<10;i++){              // Start control LED to blink showing new calibratin was made sucessfully
      digitalWrite(LEDPIN, LOW);
      delay(50);
      digitalWrite(LEDPIN, HIGH);
      delay(50);
    }
  }
}

// --------------------------------------------------------------------
// Function to read in analog sensor signal for a while as 
// first measurements are not accurate
// --------------------------------------------------------------------
void start_sensor(void)
{
  const int NUM_OF_READ = 1000;    // number of read cycles not used for "window" control
  int i=0;                        // because the sensor must get warmed up first.
  
  for(i=0;i<NUM_OF_READ;i++)      // for loop
  {
    analogRead(sensorPin);        // read the sensor in
    delay(10);                    // delay by 10ms
  }
} 

// --------------------------------------------------------------------
// Function to read in analog sensor signal and make a "Mittelwert"
// This is because the sensor signal turned out to be very unstable
// --------------------------------------------------------------------
void Read_CO2_Sensor(void)
{
  const int NUM_OF_READ = 200;
  float new_value = 0.0;

  int i=0;
  
  for(i=0;i<NUM_OF_READ;i++)                // for loop reading in NUM_OF_READ sensor vlues and make average
  {                                         // as the sensor is not really stable
    new_value = analogRead(sensorPin);      // read the sensor in
    sensorValue = sensorValue + new_value;  // add to the last sum of sensor values
    delay(10);                              // delay by 10ms
  }
  sensorValue = sensorValue/NUM_OF_READ;    // devide by number of read ins
}

// --------------------------------------------------------------------
// Function closing the window by control of servo motor
// --------------------------------------------------------------------
void Window_close(void)
{
 
 window_control.attach(10);         // declare usage of PWM pin "10" 
 for(window_pos = ZU; window_pos <= AUF; window_pos++)
  {
      window_control.write(window_pos);
      delay(25);
  }
  Serial.println(" - OPEN -");      // Show Closing status on debug window 
  window_control.attach(11);        // declare usage of PWM pin to an unused pin "11" to eliminate permanent noise of motor
                    
}

// --------------------------------------------------------------------
// Function opening the window by control of servo motor
// --------------------------------------------------------------------
void Window_open(void)
{
   tone(3, 70);                       // Make sound with the buzzer
   window_control.attach(10); // declare usage of PWM pin "10" 
   for(window_pos = AUF; window_pos >= ZU; window_pos--)
  {
      window_control.write(window_pos);
      delay(25);
  }
  Serial.println(" - CLOSE -");       // Show Closing status on debug window 
  window_control.attach(11); // declare usage of PWM pin to an unused pin "11" to eliminate permanent noise of motor

  noTone(3);                             // Stop sound
}