Controlling two servo's with an Arduino Uno

Support Servo controllers and servos
1

Hello,

I found a code on your website to control a servo with an Arduino Uno witout using a library.
https://www.pololu.com/docs/0J57/8.a
This code is for one servo, I have two servo’s to control. I changed the code for two servo’s but it didn’t work. Any idea what I’m doing wrong?
Translation of a few words:
Servo rechts = Servo right
Servo links = Servo left

This is the code I made:

[code]//Servo rechts
#define SERVO_RECHTS 10
uint16_t volatile servoTime = 0;
uint16_t volatile servoHighTime = 3000;
boolean volatile servoHigh = false;

//Servo links
#define SERVO_LINKS 11
uint16_t volatile servoTime2 = 0;
uint16_t volatile servoHighTime2 = 3000;
boolean volatile servoHigh2 = false;

ISR(TIMER2_COMPA_vect)
{
//SERVO rechts
servoTime += OCR2A + 1;

static uint16_t highTimeCopy = 3000;
static uint8_t interruptCount = 0;

if(servoHigh)
{
	if(++interruptCount == 2)
	{
		OCR2A = 255;
	}
	if(servoTime >= highTimeCopy)
	{
		digitalWrite(SERVO_RECHTS, LOW);
		servoHigh = false;
		interruptCount = 0;
	}
}
else
{
	if(servoTime >= 40000)
	{
		highTimeCopy = servoHighTime;
		digitalWrite(SERVO_RECHTS, HIGH);
		servoHigh = true;
		servoTime = 0;
		interruptCount = 0;
		OCR2A = ((highTimeCopy % 256) + 256)/2 - 1;
	}
}

//SERVO LINKS
servoTime2 += OCR2A + 1;

static uint16_t highTimeCopy2 = 3000;
static uint8_t interruptCount2 = 0;

if(servoHigh2)
{
	if(++interruptCount2 == 2)
	{
		OCR2A = 255;
	}
	if(servoTime2 >= highTimeCopy2)
	{
		digitalWrite(SERVO_LINKS, LOW);
		servoHigh2 = false;
		interruptCount2 = 0;
	}
}
else
{
	if(servoTime2 >= 40000)
	{
		highTimeCopy2 = servoHighTime2;
		digitalWrite(SERVO_LINKS, HIGH);
		servoHigh2 = true;
		servoTime2 = 0;
		interruptCount2 = 0;
		OCR2A = ((highTimeCopy2 % 256) + 256)/2 - 1;
	}
}

}

void setup()
{
pinMode(SERVO_LINKS, OUTPUT);
digitalWrite(SERVO_LINKS, LOW);
pinMode(SERVO_RECHTS, OUTPUT);
digitalWrite(SERVO_RECHTS, LOW);
TCCR2A = (1 << WGM21);
TCCR2B = (1 << CS21);
TCNT2 = 0;
OCR2A = 255;

TIMSK2 |= (1 << OCIE2A);
sei();
}

void loop()
{
servoLinks(1500); //Between 1501 and 1700 is forward, 1500 is standing still
servoRechts(1500); // Between 1499 and 1300 is backward, 1500 is standing still
}

void servoLinks(uint16_t highTimeMicroseconds)
{
TIMSK2 &= ~(1 << OCIE2A);
servoHighTime2 = highTimeMicroseconds * 2;
TIMSK2 |= (1 << OCIE2A);
}

void servoRechts(uint16_t highTimeMicroseconds)
{
TIMSK2 &= ~(1 << OCIE2A);
servoHighTime = highTimeMicroseconds * 2;
TIMSK2 |= (1 << OCIE2A);
}[/code]

Regards
Chris

PS: Sorry for my bad English

2

Hello, Chris.

This code could probably be expanded to work with more than one servo, but it looks like you simply duplicated a lot of the code and changed one copy to be for your second servo. The modification necessary to make this change would be more involved than that (e.g. you would need to understand more about what the code is doing and think about how to schedule the interrupt).

You might find this “Simple microcontroller approach to controlling a servo” blog post helpful for getting a better understanding of the concept. Also, this “Advanced hobby servo control pulse generation using hardware PWM” blog post helps explain more about interrupts.

-Brandon

3

Thank you for your replay. After the holidays I will read the pages you suggest. Thank you!