6.3 High Temperature Alarm

Next, we will make a high temperature alarm device using thermistor, push button, potentiometer and LCD. The LCD1602 shows the temperature detected by the thermistor and the high temperature threshold value, which can be adjusted using a potentiometer. The threshold value is stored on EEPROM at the same time, so if the current temperature exceeds the threshold value, the buzzer will sound.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
3 in 1 Starter Kit	380+	3 in 1 Starter Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
SunFounder R3 Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
Buzzer	-
Button	BUY
I2C LCD1602	BUY
Thermistor	BUY
Potentiometer	BUY

Schematic

Wiring

Code

Note

• You can open the file 6.3.high_tem_alarm.ino under the path of 3in1-kit\basic_project\6.3.high_tem_alarm directly.

• Or copy this code into Arduino IDE 1/2.

• The LiquidCrystal I2C library is used here, you can install it from the Library Manager.

  

After the code is successfully uploaded, The LCD1602 shows the temperature detected by the thermistor and the high temperature threshold value, which can be adjusted using a potentiometer. The threshold value is stored on EEPROM at the same time, so if the current temperature exceeds the threshold value, the buzzer will sound.

Note

If the code and wiring are fine, but the LCD still does not display content, you can turn the potentiometer on the back.

How it works?

1. Initialize the button, buzzer and I2C LCD1602, and read the EEPROM values. An interrupt is also used here to read the button status.

   void setup()
   {
       pinMode(buzzerPin, OUTPUT);
       pinMode(buttonPin, INPUT);
       lcd.init();
       lcd.backlight();
       upperTem = EEPROM.read(0);
       delay(1000);
       attachInterrupt(digitalPinToInterrupt(buttonPin), buttonState, FALLING);
   }
   

   • The interrupt is used here to read the button’s state. When the button is pressed, buttonPin changes from low to high.

   • The function buttonState is called when the interrupt triggers, and it toggles the value of the variable state.

   • FALLING means the interrupt occurs when buttonPin goes from low to high.

2. To set the high temperature threshold, the function upperTemSetting() is called when state is 1 (state switches between 0 and 1 with button press) in the main program, otherwise monitoringTemp() is called to display the current temperature and the set threshold.

   void loop()
   {
       if (state == 1)
       {
           upperTemSetting();
       }
       else {
           monitoringTemp();
       }
   }
   

3. About upperTemSetting() function.

   void upperTemSetting()
   {
       int setTem = 0;
   
       lcd.clear();
       lcd.setCursor(0, 0);
       lcd.print("Adjusting...");
       lcd.setCursor(0, 1);
       lcd.print("Upper Tem: ");
   
       while (1) {
           lcd.setCursor(11, 1);
           setTem = map(analogRead(potPin), 0, 1023, 0, 100);
           lcd.print(setTem);
           if (state == 0)
           {
               EEPROM.write(0, setTem);
               upperTem = setTem;
               lcd.clear();
               return;
           }
       }
   }
   

   • A threshold can be set with this function. When you enter this function, the LCD1602 displays the current threshold value, which can be modified using the potentiometer. This threshold value will be stored in EEPROM and exited when the button is pressed again.

4. About monitoringTemp() function.

   void monitoringTemp()
   {
   long a = analogRead(temPin);
   float tempC = beta / (log((1025.0 * 10 / a - 10) / 10) + beta / 298.0) - 273.0;
   float tempF = 1.8 * tempC + 32.0;
   lcd.setCursor(0, 0);
   lcd.print("Temp: ");
   lcd.print(tempC);
   lcd.print(char(223));
   lcd.print("C   ");
   lcd.setCursor(0, 1);
   lcd.print("Upper: ");
   lcd.print(upperTem);
   lcd.print(char(223));
   lcd.print("C   ");
   delay(300);
   if (tempC >= upperTem)
   {
       digitalWrite(buzzerPin, HIGH);
       delay(50);
       digitalWrite(buzzerPin, LOW);
       delay(10);
   }
   else
   {
       digitalWrite(buzzerPin, LOW);
   }
   }
   

   • Using this function, you can display temperature and set an alarm.

   • The thermistor value is read and then converted to Celsius temperature by the formula and displayed on the LCD1602.

   • The set threshold is also displayed on the LCD.

   • If the current temperature is greater than the threshold, the buzzer will sound an alarm.