Tau-Punkt-Lueftung/Taupunkt/Taupunkt.ino

// load library for display
#include <LiquidCrystal.h>
// load library for DHT22 sensor
#include <DHT22.h>

#define TRESHOLD   2
#define HYSTERESIS 1   
#define MIN_OUT_TEMP 5 // °C

#define RELAY_PIN 5

#define DHT22_OUTSIDE_PIN 6
#define DHT22_INSIDE_PIN 7

#define LCD_D7_PIN  8
#define LCD_D6_PIN  9
#define LCD_D5_PIN 10
#define LCD_D4_PIN 11
#define LCD_EN_PIN 12
#define LCD_RS_PIN 13


// create objects for sensor communication
DHT22 dht22inside(DHT22_INSIDE_PIN);
DHT22 dht22outside(DHT22_OUTSIDE_PIN);

// create object for LCD communication
LiquidCrystal lcd(LCD_RS_PIN, LCD_EN_PIN, LCD_D4_PIN, LCD_D5_PIN, LCD_D6_PIN, LCD_D7_PIN);

// these variables are used to capture error states of the sensors:
int inside_state = 0;
int outside_state = 0;

// these variables hold measures from the sensors
float inside_temp = 0, outside_temp = 0, inside_humi = 0, outside_humi = 0;

// these arrays are used to create some special characters for the LCD
byte degree[8] = {
  0b00010,
  0b00101,
  0b00010,
  0b00000,
  0b00000,
  0b00000,
  0b00000,
  0b00000
};

byte tau[8] = {
  0b00000,
  0b00000,
  0b11110,
  0b01000,
  0b01000,
  0b01001,
  0b00110,
  0b00000
};

byte on[8] = {
  0b11111,
  0b10001,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b10001,
  0b11111
};

byte off[8] = {
  0b11111,
  0b10001,
  0b10001,
  0b10001,
  0b10001,
  0b10001,
  0b10001,
  0b11111
};


void setup() {
  // set up the LCD
  lcd.begin(16, 4);
  lcd.createChar(0, degree); 
  lcd.createChar(1, tau); 
  lcd.createChar(2, on); 
  lcd.createChar(3, off); 

  // prepare "table" on LCD
  lcd.setCursor(0,0);
  lcd.print("     IN   OUT");
  
  lcd.setCursor(0,1);
  lcd.print("Temp   .    . ");
  lcd.write((int)0);
  lcd.print("C");
  
  lcd.setCursor(0,2);
  lcd.print("Humi   .    .  %");
  
  lcd.setCursor(0,3);
  lcd.print("   ");
  lcd.write((int)1);
  lcd.print("   .    . ");
  lcd.write((int)0);
  lcd.print("C");


  // set up the relay
  pinMode(RELAY_PIN,OUTPUT);

  // TODO: is this needed any longer?
  pinMode(4,OUTPUT);
  digitalWrite(4,LOW);
}

void printVal(float v){
  if (v<10) lcd.print(" ");
  lcd.print(v,1);
}

void relayOff(){
  lcd.setCursor(0,0);
  lcd.print("OFF");
  digitalWrite(RELAY_PIN,LOW);
}

void relayOn(){
  lcd.setCursor(0,0);
  lcd.print("ON ");
  digitalWrite(RELAY_PIN,HIGH);
}

void fehler(int col, int code){
    lcd.setCursor(col,1);    
    lcd.print("Err ");    
    lcd.setCursor(col,2);
    lcd.print("  ");
    lcd.print(code);
    lcd.print(" ");
    lcd.setCursor(col,3);  
    lcd.print("--- ");
    relayOff();
}

float taupunkt(float t, float r) {  
  float a, b;
  
  if (t >= 0) {
    a = 7.5;
    b = 237.3;
  } else {
    a = 7.6;
    b = 240.7;
  }
  
  // Sättigungsdampfdruck in hPa
  float sdd = 6.1078 * pow(10, (a*t)/(b+t));
  
  // Dampfdruck in hPa
  float dd = sdd * (r/100);
  
  // v-Parameter
  float v = log10(dd/6.1078);
  
  // Taupunkttemperatur (°C)
  return  (b*v) / (a-v);
}

void loop() {  
  delay(2500); // dht 22 sensor may only be read every two seconds
  inside_temp  = dht22inside.getTemperature();
  inside_humi  = dht22inside.getHumidity();
  inside_state = dht22inside.getLastError();
  outside_temp  = dht22outside.getTemperature();
  outside_humi  = dht22outside.getHumidity();
  outside_state = dht22outside.getLastError();
  
  boolean inside_error = false, outside_error = false;
  
  if (inside_state != dht22inside.OK || isnan(inside_temp)||isnan(inside_humi)) {    
    fehler(5,inside_state);
    inside_error = true;
  } else {    
    if (inside_temp<-40 || inside_temp>80){
      lcd.setCursor(5,1);    
      lcd.print("OOR!"); // out of range!
      inside_error = true;
    } else {
      lcd.setCursor(5,1);    
      printVal(inside_temp);      
    }
    if (inside_humi<0 || inside_humi>100){
      lcd.setCursor(5,2);    
      lcd.print("OOR!"); // out of range
      inside_error = true;
    } else {
      lcd.setCursor(5,2);
      printVal(inside_humi);
    }
  }

  if (outside_state != dht22outside.OK) {    
    fehler(10,outside_state);
    outside_error = true;
  } else {    
    if (outside_temp<-40 || outside_temp>80){
      lcd.setCursor(10,1);    
      lcd.print("OOR!"); // out of range!
      outside_error = true;
    } else {
      lcd.setCursor(10,1);    
      printVal(outside_temp);      
    }
    if (outside_humi<0 || outside_humi>100){
      lcd.setCursor(10,2);    
      lcd.print("ORR!"); // out of range!
      outside_error = true;
    } else {
      lcd.setCursor(10,2);
      printVal(outside_humi);
    }
  }  

  lcd.setCursor(5,3);    
  float tau_outside, tau_inside;
  if (inside_error){
    lcd.print("----");
  } else {
    tau_inside = taupunkt(inside_temp,inside_humi);    
    printVal(tau_inside);
  }

  lcd.setCursor(10,3); 
  if (outside_error){
    lcd.print("----");
  } else {
    tau_outside = taupunkt(outside_temp,outside_humi);    
    printVal(tau_outside);    
  }  

  if (inside_error || outside_error || outside_temp < MIN_OUT_TEMP){
    relayOff();
  } else {
    if (tau_inside > tau_outside + TRESHOLD + HYSTERESIS) {
      relayOn();
    } 
    if (tau_inside < tau_outside + TRESHOLD) {
      relayOff();
    }
  }
}