const int output_1 = 9;
const int output_2 = 10;
const int output_3 = 11;
const int t = 2770;
        //t = 2777; // t*6 = 16662 uS  ===> f = 1/(t*6) = 60.0168 = 60 Hz
        //t = 3310; // t*6 = 19860 uS  ===> f = 1/(t*6) = 50.3524 = 50 Hz
void setup()
{
  pinMode(output_1, OUTPUT); // Phase 1
  pinMode(output_2, OUTPUT); // Phase 2
  pinMode(output_3, OUTPUT); // Phase 3
}
void loop()
{
  delayMicroseconds(t);
  digitalWrite(output_1, LOW);
  delayMicroseconds(t);
  digitalWrite(output_2, HIGH);
  delayMicroseconds(t);
  digitalWrite(output_3, LOW);
  delayMicroseconds(t);
  digitalWrite(output_1, HIGH);
  delayMicroseconds(t);
  digitalWrite(output_2, LOW);
  delayMicroseconds(t);
  digitalWrite(output_3, HIGH);
}