help: servo motor

can i change the direction of servo motor by change polarity ?
if not
how can i change the direction of servo motor by using pic 16f877a?
i use servo motori sys s3006
3 wire
void main()
{
int x;
trisb=0;
trisd=0;
portb=0;
portd=0;

for(x=0;x<4;x++)
{
PORTB.F0 = 1;
Delay_us(1000);//1ms Delay
PORTB.F0 = 0;

Delay_us(1000);

}
}
connect single wire to port b pin 0 in pic
i read some threads about change delay time to change direction
but it do not work
help please
thanks

 

To control an RC servo you will need to use PWM with a duty‐cycle of 20ms, and the pulse width contained within those 20ms varies from 1ms to 2ms.

This variation in the pulse width is what controls the servo. As a rule of thumb, if a 1ms
pulse is constantly fed to the servo, it will position itself around ‐60° angle,
1.5ms and it will go to the center (0°), and 2 ms will position the servo at +60°
angle.

Here is an example using a pic16f877a written in Mikropascal:

Code ( (Unknown Language)):

1. //designed for a PIC16F877A with a 4Mhz clock
2. interrupt {
3.      if (TMR0IF flag is raised) {
4.           flagServo = true;
5.           TMR0 := 100;
6.           SetBit(INTCON,TMR0IE);
7.           ClearBit(INTCON,TMR0IF);
8.      }
9. }
10. main_body {
11.      TRISC = 0;
12.      delay = 1000; //-60
13.      increment := 1;
14.      steps := 10; //10 steps = approx. 1 degree
15.      OPTION_REG := $86; //setup TMR0 to trigger
16.      TMR0 := 100; //every 20ms
17.      SetBit(INTCON,GIE);
18.      SetBit(INTCON,TMR0IE);
19.      while (1==1) {
20.           if (flagServo) {
21.           //generate pulse with width = “delay” microseconds
22.               SetBit(PORTC,0);
23.               delay_microseconds(delay);
24.               ClearBit(PORTC,0);
25.          //increase/decrease angle
26.              delay = delay + increment * steps;
27.              if (delay > 2000) {
28.                     delay = 1999;
29.                     increment = -1;
30.             } else if (delay < 900) {
31.                     delay = 901;
32.                     increment = 1;
33.                     }
34.           flagServo = false;
35.           }
36.      }
37. }
38.  

 

thanks of replay
ok if i want to do that with normal pin not pwm pin
i need to change pulse wide time to reverse direction
i try use (.7ms or 2ms ) to change direction but do not work
void main()
{
int x;
trisb=0;
trisd=0;
portb=0;
portd=0;

for(x=0;x<4;x++)
{
PORTB.F0 = 1;
Delay_us(700);
PORTB.F0 = 0;

Delay_ms(1000);

}
}
and this
void main()
{
int x;
trisb=0;
trisd=0;
portb=0;
portd=0;

for(x=0;x<4;x++)
{
PORTB.F0 = 1;
Delay_us(2000);
PORTB.F0 = 0;

Delay_ms(1000);

}
}
what i missed ?
if i change the polarity like dc motor direction will change or motor will damage ?

 

instead of 1000ms you want 20ms, and if you reverse the polarity it could damage the motor, it certainly wouldn't do what you want.

 

Here is another link that shows how servomotors work. http://www.lynxmotion.com/images/html/servo01.htm

Reversing polarity will damage the servo circuitry that allows it to rotate the motor back and forth in a range of 180 degrees.

 

I don't see why you are having issues, when the site you got the circuit from provides the code to run the servo..... you just need to modify it to suit your needs, (and write it in the appropriate compiler language since this is written in MicroC)....

Code ( (Unknown Language)):

1. void main()
2. {
3.   TRISB = 0; // PORTB as Ouput Port
4.   do
5.   {
6.    //To Turn to 0 Degree
7.    PORTB.F0 = 1;
8.    Delay_us(1000);//1ms Delay
9.    PORTB.F0 = 0;
10.  
11.    Delay_ms(1000);
12.  
13.    //To Turn to 90 Degree
14.    PORTB.F0 = 1;
15.    Delay_us(1500);
16.    PORTB.F0 = 0;
17.  
18.    Delay_ms(1000);
19.  
20.    //To Turn to 180 Degree
21.    PORTB.F0 = 1;
22.    Delay_us(2000);
23.    PORTB.F0 = 0;
24.  
25.    Delay_ms(1000);
26.  }while(1);
27. }

 

OK, so I had to try it to see if the code works.... I am using Hi-tech C with a Pic16f887 running at 20Mhz.... this will run the servo from one end to the other looping it constantly... (Just change the word Servo to the I/O pin you are using.....)

Code ( (Unknown Language)):

1. void Move_Servo()
2. {
3.     int x;
4.     while(1){
5.         //to turn to 0 degrees
6.         for (x=0;x<25;x++){
7.             Servo = 1;
8.             DelayMs(1);
9.             Servo = 0;
10.             DelayMs(10);
11.         }//end for
12.  
13.     DelayMs(1000);  //short delay between moves
14.    
15.         //to turn it all the way to 180
16.         for (x=0;x<25;x++){
17.             Servo = 1;
18.             DelayMs(2);
19.             Servo = 0;
20.             DelayMs(10);
21.         }//end for
22.     };//end while
23. }

 

thanks for replay
i make delay (delay_us(3000)
it work nice
thanks again