3.1.7 Overheat Monitor

Introduction

You may want to make an overheat monitoring device that applies to various situations, ex., in the factory, if we want to have an alarm and the timely automatic turning off of the machine when there is a circuit overheating. In this project, we will use thermistor, joystick, buzzer, LED and LCD to make an smart temperature monitoring device whose threshold is adjustable.

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
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
Joystick Module	-
ADC0834	-
Transistor	BUY
I2C LCD1602	BUY
Thermistor	BUY
Buzzer	-

Schematic Diagram

T-Board Name	physical	wiringPi	BCM
GPIO17	Pin 11	0	17
GPIO18	Pin 12	1	18
GPIO27	Pin 13	2	27
GPIO22	Pin15	3	22
GPIO23	Pin16	4	23
GPIO24	Pin18	5	24
SDA1	Pin 3
SCL1	Pin 5

Experimental Procedures

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

cd ~/raphael-kit/c/3.1.7/

Step 3: Compile the code.

gcc 3.1.7_OverheatMonitor.c -lm -lwiringPi

Step 4: Run the executable file.

sudo ./a.out

As the code runs, the current temperature and the high-temperature threshold 40 are displayed on I2C LCD1602. If the current temperature is larger than the threshold, the buzzer and LED are started to alarm you.

Joystick here is for your pressing to adjust the high-temperature threshold. Toggling the Joystick in the direction of X-axis and Y-axis can adjust (turn up or down) the current high-temperature threshold. Press the Joystick once again to reset the threshold to initial value.

Note

• If there is an error prompt wiringPi.h: No such file or directory, please refer to Install and Check the WiringPi.

• If you get Unable to open I2C device: No such file or directory error, you need to refer to I2C Configuration to enable I2C and check if the wiring is correct.

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

Code Explanation

int get_joystick_value(){
    uchar x_val;
    uchar y_val;
    x_val = get_ADC_Result(1);
    y_val = get_ADC_Result(2);
    if (x_val > 200){
        return 1;
    }
    else if(x_val < 50){
        return -1;
    }
    else if(y_val > 200){
        return -10;
    }
    else if(y_val < 50){
        return 10;
    }
    else{
        return 0;
    }
}

This function reads values of X and Y. If X>200, there will return 1; X<50, return -1; y>200, return -10, and y<50, return 10.

void upper_tem_setting(){
    write(0, 0, "Upper Adjust:");
    int change = get_joystick_value();
    upperTem = upperTem + change;
    char str[6];
    snprintf(str,3,"%d",upperTem);
write(0,1,str);
int len;
  len = strlen(str);
  write(len,1,"             ");
    delay(100);
}

This function is for adjusting the threshold and displaying it on the I2C LCD1602.

double temperature(){
    unsigned char temp_value;
    double Vr, Rt, temp, cel, Fah;
    temp_value = get_ADC_Result(0);
    Vr = 5 * (double)(temp_value) / 255;
    Rt = 10000 * (double)(Vr) / (5 - (double)(Vr));
    temp = 1 / (((log(Rt/10000)) / 3950)+(1 / (273.15 + 25)));
    cel = temp - 273.15;
    Fah = cel * 1.8 +32;
    return cel;
}

Read the analog value of the CH0 (thermistor) of ADC0834 and then convert it to temperature value.

void monitoring_temp(){
    char str[6];
    double cel = temperature();
    snprintf(str,6,"%.2f",cel);
    write(0, 0, "Temp: ");
    write(6, 0, str);
    snprintf(str,3,"%d",upperTem);
    write(0, 1, "Upper: ");
    write(7, 1, str);
    delay(100);
    if(cel >= upperTem){
        digitalWrite(buzzPin, HIGH);
        digitalWrite(LedPin, HIGH);
    }
    else if(cel < upperTem){
        digitalWrite(buzzPin, LOW);
        digitalWrite(LedPin, LOW);
    }
}

As the code runs, the current temperature and the high-temperature threshold 40 are displayed on I2C LCD1602. If the current temperature is larger than the threshold, the buzzer and LED are started to alarm you.

int main(void)
{
    setup();
    int lastState =1;
    int stage=0;
    while (1)
    {
        int currentState = digitalRead(Joy_BtnPin);
        if(currentState==1 && lastState == 0){
            stage=(stage+1)%2;
            delay(100);
            lcd_clear();
        }
        lastState=currentState;
        if (stage==1){
            upper_tem_setting();
        }
        else{
            monitoring_temp();
        }
    }
    return 0;
}

The function main() contains the whole program process as shown:

1. When the program starts, the initial value of stage is 0, and the current temperature and the high-temperature threshold 40 are displayed on I2C LCD1602. If the current temperature is larger than the threshold, the buzzer and the LED are started to alarm you.

2. Press the Joystick, and stage will be 1 and you can adjust the high-temperature threshold. Toggling the Joystick in the direction of X-axis and Y-axis can adjust (turn up or down) the current threshold. Press the Joystick once again to reset the threshold to initial value.

Phenomenon Picture