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3.1.8 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 lesson, we will use thermistor, joystick, buzzer,
LED and LCD to make an smart temperature monitoring device whose
threshold is adjustable.

Components
-----------------

.. image:: img/list_Overheat_Monitor.png
    :align: center

.. image:: img/list_Overheat_Monitor2.png
    :align: center

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             
============ ======== ======== ===

.. image:: img/Schematic_three_one8.png
   :width: 700
   :align: center

Experimental Procedures
-----------------------------

**Step 1:** Build the circuit.

.. image:: img/image258.png
   :width: 800

**Step 2**: Go to the folder of the code.

.. raw:: html

   <run></run>

.. code-block:: 

    cd ~/davinci-kit-for-raspberry-pi/c/3.1.8/

**Step 3**: Compile the code.

.. raw:: html

   <run></run>

.. code-block:: 

    gcc 3.1.8_OverheatMonitor.c -lwiringPi -lm

**Step 4**: Run the executable file.

.. raw:: html

   <run></run>

.. code-block:: 

    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.

.. note::

    If it does not work after running, or there is an error prompt: \"wiringPi.h: No such file or directory\", please refer to :ref:`C code is not working?`.


**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.

**Code Explanation**

.. code-block:: c

    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**\".

.. code-block:: c

    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.

.. code-block:: c

    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.

.. code-block:: c

    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.

.. code-block:: c

    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.