Access

Right now I am using an Atmel AVR microcontroller (atmega16 series, clock speed = 8MHz) to actuate a servo.
To actuate the servo, the microcontroller generates the PWM signal (instead of an RC receiver).
My question is, how many individual 'steps' (positions) does an individual servo have; is it 256 or is it more? And is it standard or does it differ from servo to servo?

Right now I am using a Futaba S3004 and even with 256 different PWM pulse settings it still seems to jerk a bit rather than move smoothly.
I know it has a least 256 since I already tried 1/256 and 1/1024 timer prescaler settings (see below) and there is a definate improvement in smoothness going to the 1/64 timer prescaler setting. Will I gain even more precision if I go to a timer prescaler setting of 1/8, which will also force me to use the 16-bit timer? I figured I'd ask first, maybe someone else has already done the same thing and I don't want to have to rework everything for no benefit.

This is my interrupt handler that actually moves the servo:
prescaler is set in this line: "TCCR0 = _BV (CS01) | _BV (CS00); // prescaler = 1/64"

SIGNAL (SIG_OUTPUT_COMPARE0) {
/*
// full interrupt-driven implementation
if (cp_state == CP_STATE_DOWN) {
PORTA |= 0x80;
cp_state = CP_STATE_UP;
OCR0 = TIME_INITIAL + servo_up;
} else if (cp_state == CP_STATE_UP) {
PORTA &= 0x7f;
cp_state = CP_STATE_DOWN;
TCNT0 = 0;
OCR0 = TIME_INITIAL;
}
*/

// blocking implementation
TCCR0 = _BV (CS01) | _BV (CS00); // prescaler = 1/64

PORTA |= 0x80;
cp_state = CP_STATE_UP;

TCNT0 = 0;
while (TCNT0 < (SERVO_PREWAIT))
;

TCNT0 = 0;
if (servo_up < 128) {
while (TCNT0 < servo_up * SERVO_MULTIPLIER)
;
} else {
while (TCNT0 < 128)
;
TCNT0 = 0;
uint8_t servo_up_minus;
servo_up_minus = servo_up - 128;
while (TCNT0 < servo_up_minus * SERVO_MULTIPLIER)
;
}

PORTA &= 0x7f;
cp_state = CP_STATE_DOWN;
TCCR0 = _BV (CS02) | _BV (CS00);
TCNT0 = 0;
}

I know the blocking implementation is non-optimal but I don't think a full interrupt-driven implemention could later be expanded to control multiple servos.

dirtybird

My Feedback: (5)

Since it really is an analog servo, the S3004 theoretically has infinite steps. PCM systems found that 512 digital steps was not adaquate so switched to 1028. There is a system now available that has 2048 steps but I think that is gilding the lilly.