Wood smoker temperature controller

1// Temperature controller code for a smoker
2// Temperature of the smoker is measured by a K-type thermocouple with a MAX6675 amplifier board.
3// Temperature of the smoker is controlled by a SG90 servo and a 12v fan.
4// When the temperature is below MIN_TEMP the servo opens the airway into the smoker using a flap and turns on a fan to provide air for the fire
5// When the temperature rises above MAX_TEMP the servo closes the airway into the smoker using the flap and turns off the fan to stop the temperature from rising
6
7#include <LiquidCrystal.h>
8#include "max6675.h"
9#include <Servo.h>
10
11// LCD1602 screen without a 2IC unit
12const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
13
14// Max and min temperature witch can be set by the potentiometers
15const int MAX_TEMP = 300;
16const int MIN_TEMP = 0;
17
18// Number of readings for potentiometer values
19const int NUM_READINGS = 100;
20
21const int relay = 9;
22
23// MAX6675 pins
24int soPin = 6;
25int csPin = 7;
26int sckPin = 8;
27
28// Variables
29float temperature = 0.0;
30int lowerLimit = 0;
31int upperLimit = 0;
32
33// Objects
34LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
35MAX6675 thermocouple(sckPin, csPin, soPin);
36Servo servo;
37
38
39void setup() {
40  servo.write(0);
41  servo.attach(10);
42  lcd.begin(16,2);
43  lcd.clear();
44  pinMode(relay, OUTPUT);
45  digitalWrite(relay, LOW);
46  delay(1000); // Waits for the MAX6675 to stabilize
47}
48
49
50void loop() {
51  readTemperatures();
52  printTemperature();
53  control(); 
54  delay(1000);
55}
56
57
58// Reads the smoker temperature and limits set by potentiometers.
59void readTemperatures() {
60
61  unsigned long lowerSum = 0;
62  unsigned long upperSum = 0;
63  temperature = thermocouple.readCelsius();
64
65  // Reads the potentiometer values NUM_READINGS times and calculates the averages to get consistent values for the limits
66  for (int i = 0; i < NUM_READINGS; i++) {
67    lowerSum += map(analogRead(A2), 0, 1023, MIN_TEMP, MAX_TEMP);
68    upperSum += map(analogRead(A3), 0, 1023, MIN_TEMP, MAX_TEMP);
69  }
70  lowerLimit = lowerSum / NUM_READINGS;
71  upperLimit = upperSum / NUM_READINGS;
72}
73
74
75// Controls the SG90 servo and 12v fan according to the temperature
76void control(){     
77
78  if(lowerLimit > temperature){
79    digitalWrite(relay, HIGH);
80    servo.write(0);
81  }
82  else if(upperLimit < temperature){
83    digitalWrite(relay, LOW); 
84    servo.write(160);
85  }
86}
87
88
89// Prints the lower and upper limit on the LCD screen
90// Printed text is in finnish but you can change it to your desired language.
91void printTemperature(){
92  
93  // Lower limit
94  lcd.setCursor(0,0);
95  lcd.print("Alaraja = ");
96  lcd.print(lowerLimit);
97  lcd.print((char)223);
98  lcd.print("C           ");
99
100  // Upper limit
101  lcd.setCursor(0,1);
102  lcd.print("Ylaraja = ");
103  lcd.print(upperLimit);
104  lcd.print((char)223);
105  lcd.print("C            ");
106  lcd.setCursor(0,0);
107}