8.b. Controlling a servo with an Arduino Leonardo or A-Star 32U4 Prime
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 or A-Star 32U4 Prime. The modified Servo library does not interfere
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// 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
}
Pololu Zumo Shield for Arduino User’s Guide
© 2001–2019 Pololu Corporation
8. Controlling a servo
Page 51 of 52
