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Best way to control a servo?

Mike Akkerman

Hi,

This might be a little OT but I've been exploring a few new ways of controling a servo.

I'm using a 8051 board of my own design, a Hitec HS300BB servo and the control line of the servo is connected to a digital out line.

Up untill now I've been using code similar to this:

sbit P1_1 = P1^1;
unsigned int wait;

P1_1 = 1;
for(x = 0; x <= wait; x++);
P1_1 = 0;
for(x = 0; x <= wait; x++);

This solution works but it isn't a very nice way of doing it cause it's strongly depended on lots os variables like overhead and processing power.

For my question, what is considerd to be the best way of controlling a servo which isn't as sensitive for overhead? (with the material I have ofcourse) Some example code would be apriciated.

TIA,
Mike

Parents
  • 0 in reply to Drew Davis

    Here's what I figured out using a Timer 2 example I found on the Keil site:

    void init_timer2 (void) {
	/*--------------------------------------
	Set the reload values to be 20000 clocks.
	--------------------------------------*/
	CRCL = (65535UL-0000UL);
	CRCH = (65535UL-20000UL) >> 8;

	CCEN = 0x08;

	CCL1 = (65535UL-1700UL);
	CCH1 = (65535UL-1700UL) >> 8;

	TL2 = CRCL;
	TH2 = CRCH;

	/*--------------------------------------
	Set Timer2 for 16-bit auto-reload.
	The timer counts to 0xFFFF, overflows,
	is reloaded, and generates an interrupt.
	--------------------------------------*/
	T2CON = 0x11;                /* 0XX10001 */


	/*--------------------------------------
	--------------------------------------*/
	ET2 = 1;                      /* Enable Timer 2 Interrupts */
	EAL = 1;                      /* Global Interrupt Enable */

	P5 = 0x18;
}

void timer1_ISR (void) interrupt 5 {
	TF2 = 0;
}

    I've set it to reload every 20000 systemticks (1MHz / 20Khz = 50Hz) which should generate a interupt every 20 ms.

    So far everything okay... But I have to generate a pulse of 1.7 ms to center the servo, 8.5 ms to go absolute left and 2.5 ms to go absolute right.

    Am I doing something wrong or is this a defective servo?

Reply
  • 0 in reply to Drew Davis

    Here's what I figured out using a Timer 2 example I found on the Keil site:

    void init_timer2 (void) {
	/*--------------------------------------
	Set the reload values to be 20000 clocks.
	--------------------------------------*/
	CRCL = (65535UL-0000UL);
	CRCH = (65535UL-20000UL) >> 8;

	CCEN = 0x08;

	CCL1 = (65535UL-1700UL);
	CCH1 = (65535UL-1700UL) >> 8;

	TL2 = CRCL;
	TH2 = CRCH;

	/*--------------------------------------
	Set Timer2 for 16-bit auto-reload.
	The timer counts to 0xFFFF, overflows,
	is reloaded, and generates an interrupt.
	--------------------------------------*/
	T2CON = 0x11;                /* 0XX10001 */


	/*--------------------------------------
	--------------------------------------*/
	ET2 = 1;                      /* Enable Timer 2 Interrupts */
	EAL = 1;                      /* Global Interrupt Enable */

	P5 = 0x18;
}

void timer1_ISR (void) interrupt 5 {
	TF2 = 0;
}

    I've set it to reload every 20000 systemticks (1MHz / 20Khz = 50Hz) which should generate a interupt every 20 ms.

    So far everything okay... But I have to generate a pulse of 1.7 ms to center the servo, 8.5 ms to go absolute left and 2.5 ms to go absolute right.

    Am I doing something wrong or is this a defective servo?

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