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3.1.4 Smart Fan

Note

Depending on your kit version, please identify whether you have ADC0834 or MCP3008 and proceed with the matching section.

Introduction

In this course, we will use motors, buttons and thermistors to make a manual + automatic smart fan whose wind speed is adjustable.

Components

Schematic Diagram

T-Board Name	physical	wiringPi	BCM
GPIO17	Pin 11	0	17
GPIO18	Pin 12	1	18
GPIO27	Pin 13	2	27
GPIO22	Pin 15	3	22
GPIO5	Pin 29	21	5
GPIO6	Pin 31	22	6
GPIO13	Pin 33	23	13

Experimental Procedures

Step 1: Build the circuit.

Note

The power module can apply a 9V battery with the 9V Battery Buckle in the kit. Insert the jumper cap of the power module into the 5V bus strips of the breadboard.

For C Language Users

Step 2: Get into the folder of the code.

cd ~/davinci-kit-for-raspberry-pi/c/3.1.4/

Step 3: Compile.

gcc 3.1.4_SmartFan.c -lwiringPi -lm

Step 4: Run the executable file above.

sudo ./a.out

As the code runs, start the fan by pressing the button. Every time you press, 1 speed grade is adjusted up or down. There are 5 kinds of speed grades: 0~4. When set to the 4^th speed grade and you press the button, the fan stops working with a 0 wind speed.

Note

If it does not work after running, or there is an error prompt: "wiringPi.h: No such file or directory", please refer to Install and Check the WiringPi.

Once the temperature goes up or down for more than 2℃, the speed automatically gets 1-grade faster or slower.

Code Explanation

int temperture(){
    unsigned char analogVal;
    double Vr, Rt, temp, cel, Fah;
    analogVal = get_ADC_Result(0);
    Vr = 5 * (double)(analogVal) / 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;
    int t=cel;
    return t;
}

Temperture() works by converting thermistor values read by ADC0834 into temperature values. Refer to 2.2.2 Thermistor for more details.

int motor(int level){
    if(level==0){
        digitalWrite(MotorEnable,LOW);
        return 0;
    }
    if (level>=4){
        level =4;
    }
    digitalWrite(MotorEnable,HIGH);
    softPwmWrite(MotorPin1, level*25);
    return level;
}

This function controls the rotating speed of the motor. The range of the Level: 0-4 (level 0 stops the working motor). One level adjustment stands for a 25% change of the wind speed.

int main(void)
{
    setup();
    int currentState,lastState=0;
    int level = 0;
    int currentTemp,markTemp=0;
    while(1){
        currentState=digitalRead(BtnPin);
        currentTemp=temperture();
        if (currentTemp<=0){continue;}
        if (currentState==1&&lastState==0){
            level=(level+1)%5;
            markTemp=currentTemp;
            delay(500);
        }
        lastState=currentState;
        if (level!=0){
            if (currentTemp-markTemp<=-2){
                level=level-1;
                markTemp=currentTemp;
            }
            if (currentTemp-markTemp>=2){
                level=level+1;
                markTemp=currentTemp;
            }
        }
        level=motor(level);
    }
    return 0;
}

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

Constantly read the button state and the current temperature.
Every press makes level+1 and at the same time, the temperature is updated. The Level ranges 1~4.
As the fan works ( the level is not 0), the temperature is under detection. A 2℃+ change causes the up and down of the level.
The motor changes the rotating speed with the Level.