1.3.2 Servo¶

Introduction¶

In this project, we will learn how to make the servo rotate.

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
Servo	BUY

Schematic Diagram¶

Experimental Procedures¶

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

cd ~/raphael-kit/c/1.3.2

Step 3: Compile the code.

gcc 1.3.2_Servo.c -lwiringPi

Step 4: Run the executable file.

sudo ./a.out

After the program is executed, the servo will rotate from 0 degrees to 180 degrees, and then from 180 degrees to 0 degrees, circularly.

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.

Code

#include <wiringPi.h>
#include <softPwm.h>
#include <stdio.h>

#define ServoPin    1       //define the servo to GPIO1
long Map(long value,long fromLow,long fromHigh,long toLow,long toHigh){
    return (toHigh-toLow)*(value-fromLow) / (fromHigh-fromLow) + toLow;
}
void setAngle(int pin, int angle){    //Create a funtion to control the angle of the servo.
    if(angle < 0)
        angle = 0;
    if(angle > 180)
        angle = 180;
    softPwmWrite(pin,Map(angle, 0, 180, 5, 25));
}

int main(void)
{
    int i;
    if(wiringPiSetup() == -1){ //when initialize wiring failed,print message to screen
        printf("setup wiringPi failed !");
        return 1;
    }
    softPwmCreate(ServoPin, 0, 200);       //initialize PMW pin of servo
    while(1){
        for(i=0;i<181;i++){     // Let servo rotate from 0 to 180.                  setAngle(ServoPin,i);
            delay(2);
        }
        delay(1000);
        for(i=181;i>-1;i--){        // Let servo rotate from 180 to 0.              setAngle(ServoPin,i);
            delay(2);
        }
        delay(1000);
    }
    return 0;
}

Code Explanation

long Map(long value,long fromLow,long fromHigh,long toLow,long toHigh){
    return (toHigh-toLow)*(value-fromLow) / (fromHigh-fromLow) + toLow;
}

Create a Map() function to map value in the following code.

void setAngle(int pin, int angle){    //Create a funtion to control the angle of the servo.
    if(angle < 0)
        angle = 0;
    if(angle > 180)
        angle = 180;
    softPwmWrite(pin,Map(angle, 0, 180, 5, 25));
}

Create a funtion, setAngle() to write angle to the servo.

softPwmWrite(pin,Map(angle,0,180,5,25));

This function can change the duty cycle of the PWM.

To make the servo rotate to 0 ~ 180 °, the pulse width should change within the range of 0.5ms ~ 2.5ms when the period is 20ms; in the function, softPwmCreate() , we have set that the period is 200x100us=20ms, thus we need to map 0 ~ 180 to 5x100us ~ 25x100us.

The prototype of this function is shown below.

int softPwmCreate（int pin，int initialValue，int pwmRange）;

pin: Any GPIO pin of Raspberry Pi can be set as PWM pin.
initialValue: The initial pulse width is that initialValue times 100us.
pwmRange: the period of PWM is that pwmRange times 100us.