static uint16_t highTimeCopy = 3000;
static uint8_t interruptCount = 0;
if(servoHigh)
{
if(++interruptCount == 2)
{
OCR2A = 255;
}
// The servo pin is currently high.
// Check to see if is time for a falling edge.
// Note: We could == instead of >=.
if(servoTime >= highTimeCopy)
{
// The pin has been high enough, so do a falling edge.
digitalWrite(SERVO_PIN, LOW);
servoHigh = false;
interruptCount = 0;
}
}
else
{
// The servo pin is currently low.
if(servoTime >= 40000)
{
// We've hit the end of the period (20 ms),
// so do a rising edge.
highTimeCopy = servoHighTime;
digitalWrite(SERVO_PIN, HIGH);
servoHigh = true;
servoTime = 0;
interruptCount = 0;
OCR2A = ((highTimeCopy % 256) + 256)/2 - 1;
}
}
}
void servoInit()
{
digitalWrite(SERVO_PIN, LOW);
pinMode(SERVO_PIN, OUTPUT);
// Turn on CTC mode. Timer 2 will count up to OCR2A, then
// reset to 0 and cause an interrupt.
TCCR2A = (1 << WGM21);
// Set a 1:8 prescaler. This gives us 0.5us resolution.
TCCR2B = (1 << CS21);
// Put the timer in a good default state.
TCNT2 = 0;
OCR2A = 255;
TIMSK2 |= (1 << OCIE2A); // Enable timer compare interrupt.
sei(); // Enable interrupts.
}
void servoSetPosition(uint16_t highTimeMicroseconds)
{
TIMSK2 &= ~(1 << OCIE2A); // disable timer compare interrupt
servoHighTime = highTimeMicroseconds * 2;
TIMSK2 |= (1 << OCIE2A); // enable timer compare interrupt
}
8.b. Controlling a servo with an Arduino Leonardo
It is possible to modify the Servo library that comes with the Arduino IDE to use Timer 3 instead of Timer 1 on the
Arduino Leonardo. The modified Servo library does not interfere with the ZumoMotors library, making it possible to
simultaneously control servos and the motors.
Pololu Zumo Shield for Arduino User's Guide
© 2001–2013 Pololu Corporation
8. Controlling a servo
Page 37 of 38
