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Servo Test Driver - SG 90 and MG 90 S micro servo

 
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Bhanu Watawana



Joined: 01 Jun 2011
Posts: 15

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Servo Test Driver - SG 90 and MG 90 S micro servo
PostPosted: Wed Jun 01, 2011 7:34 pm     Reply with quote

As you have already experienced, there is no data-sheet available for above servo motors. Below posted is a simple code that you can use for getting an idea about the pulse width of the servo.


Code:


#include <16F877.h>
#device adc=8
#FUSES NOWDT, HS, NOPUT, PROTECT, NOBROWNOUT, NOLVP, NOCPD, NOWRT, NODEBUG
#use delay(clock=20000000)



/************************************************************************************************
/  Used servo - SG 90 and MG 90 S micro servo
/  Pin configuration - RED(+5) BROWN (Ground) Orange/White(Data)
/  Servo SG90 min pulse length - 500 us max pulse length - 2500 us (best performed 800 to 2300)
/  Code by Bhanu Watawana
/  0778111887
/  Uva Wellassa University - Sri Lanka
/  Mechatronics
*/////////////////////////////////////////////////////////////////////////////////////////////////

/*

How servo works
Servo motor data pin value works as a voltage reference to the motor. Inbuilt preset which turns for motor turning works
as a voltage divider and allows the reference voltage(something like PWM) to be equal to the divider voltage.

The pulse should be sent in following manner

          ____                 ____
_________|    |_______________|    |__________
         
         |time|   20 ms low   |time|
Time is the pulse width for the servo ranging 500 us to 2500 us



*/



int16 time=600;                                 // Time variable defining with initial position value - can set as desired

#define LCD_TYPE 2                              // Using LCD
#include <lcd.c>


#define servo pin_C4                            // Servo data pin defined

#int_EXT                                        // External interrupt used for input button with a pull up at B0
void  EXT_isr(void)
{

   disable_interrupts(INT_TIMER1);              // Disabling timer interrupt to stop triggering while external interrupt works
time=time+100;                                  // Always add 100 to the time of the pulse - You can change this as you wish

printf(LCD_PUTC, "\f Time is %Lu",time);        // Printing the time to the LCD - for troubleshooting
delay_ms(1000);                                 // delay for debounce

   enable_interrupts(INT_TIMER1);               // Enabling timer interrupt
}

#int_TIMER1                                     // Timer interrupt
void  TIMER1_isr(void)
{
output_high(servo);                             // Putting the data pin high
delay_us(time);                                 // Delaying the pulse for 'time' period
output_low(servo);                              // Lowering the pin
}



void main()
{
   lcd_init();

   setup_timer_1(T1_INTERNAL|T1_DIV_BY_2);      // Timer set for 26.2ms overflow with 0.4 us resolution   
                                                // This should be 20ms, but works with 10-25 ms range
   enable_interrupts(INT_EXT);
   enable_interrupts(INT_TIMER1);
   enable_interrupts(GLOBAL);
   
   
printf(LCD_PUTC, "\f TEST \nInitial- 600us");                   // For LCD debugging
delay_ms(1000);


while(true){


}

}



LCD is not needed if you can count the pulse, or just you can use Serial communication instead.
_________________
~~~~~~~~~~~~~~~~
Bhanu Watawana
Uva Wellassa University
Sri Lanka


Last edited by Bhanu Watawana on Mon Jun 13, 2011 9:39 pm; edited 1 time in total
aruna1



Joined: 14 Oct 2008
Posts: 103

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PostPosted: Mon Jun 13, 2011 9:32 pm     Reply with quote

ah ela ela
Bhanu Watawana



Joined: 01 Jun 2011
Posts: 15

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PostPosted: Mon Jun 13, 2011 9:34 pm     Reply with quote

aruna1 wrote:
ah ela ela


Thanks bro ;-)
_________________
~~~~~~~~~~~~~~~~
Bhanu Watawana
Uva Wellassa University
Sri Lanka
pacman91



Joined: 17 Jun 2011
Posts: 28
Location: Malaysia

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PostPosted: Thu Jun 30, 2011 11:15 am     Reply with quote

Quote:
setup_timer_1(T1_INTERNAL|T1_DIV_BY_2); // Timer set for 26.2ms overflow with 0.4 us resolution


20Mhz/4/2 = 0.4us

how to set the 26.2ms???
why 0.4us = 26.2ms
how to calculate
Bhanu Watawana



Joined: 01 Jun 2011
Posts: 15

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Re: Pacman
PostPosted: Sat Jul 02, 2011 6:23 am     Reply with quote

Sorry for the delay,

Its so easy if you use the CCS PIC Wizard

http://www.ccsinfo.com/forum/viewtopic.php?t=22467

Read this and it will help you to get an idea about the timers.
_________________
~~~~~~~~~~~~~~~~
Bhanu Watawana
Uva Wellassa University
Sri Lanka
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