ledRingDisplay3.ino

volatile byte muxCount = 0;
volatile byte mask[16] = {113, 114, 116, 120, 177, 178, 180, 184, 209, 210, 212, 216, 225, 226, 228, 232};
volatile byte ledSegments1[16];
byte n=0;

void setup() {
  cli();
  DDRD = 255;  // sets Arduino pins 0 to 7 as outputs
  //timer setup
  TCCR1A = 0;
  TCCR1B = 0;
  TCNT1 = 58000;
  TCCR1B = _BV(CS10); //prescaler
  TIMSK1 = _BV(TOIE1); //enable overflow interrupt
  sei();
}

ISR(TIMER1_OVF_vect) {
  TCNT1 = 58000;
  if (ledSegments1[muxCount]) { PORTD = mask[muxCount]; } else { PORTD = 0; }
  muxCount = ++muxCount % 16;
}

void loop() {
  delay(70);
  // perform 'clear screen' 
  ledSegments1[0]=0;
  ledSegments1[1]=0;
  ledSegments1[2]=0;
  ledSegments1[3]=0;
  ledSegments1[4]=0;
  ledSegments1[5]=0;
  ledSegments1[6]=0;
  ledSegments1[7]=0;
  ledSegments1[8]=0;
  ledSegments1[9]=0;
  ledSegments1[10]=0;
  ledSegments1[11]=0;
  ledSegments1[12]=0;
  ledSegments1[13]=0;
  ledSegments1[14]=0;
  ledSegments1[15]=0;
  // bit shift
  ledSegments1[n] = 1;
  ledSegments1[(n + 8) % 16] = 1;
  n = ++n % 16;
}