Two hands on an Arduino Uno

// Two hands: a biaxial stepper is a clock face's movement, two motors on
// one axis, driven here through two A4988s in full step, a minute every
// second so it can be watched.
//
//   pin 3  outer hand's STEP   pin 4  its DIR    (the minutes)
//   pin 5  inner hand's STEP   pin 6  its DIR    (the hours)
//   both drivers: VMOT on 12 V, VDD on 5 V, RST linked to SLP, the mode pins
//   left low (full step), the grounds to the Uno's
//
// 200 full steps turn a hand once. The minute hand goes round in 60 minutes
// and the hour hand in 12 hours, so after m minutes they should have taken
// m x 200 / 60 and m x 200 / 720 steps. Neither is a whole number per
// minute, so the sketch keeps the count it owes each hand and steps until
// it has paid it, the way a Bresenham line keeps its error.

const int STEP_OUTER = 3;
const int DIR_OUTER = 4;
const int STEP_INNER = 5;
const int DIR_INNER = 6;

long minutes = 0;
long outerSteps = 0;
long innerSteps = 0;

void pulse(int pin) {
  digitalWrite(pin, HIGH);
  delayMicroseconds(5);
  digitalWrite(pin, LOW);
  delay(3);
}

void setup() {
  Serial.begin(9600);
  pinMode(STEP_OUTER, OUTPUT);
  pinMode(DIR_OUTER, OUTPUT);
  pinMode(STEP_INNER, OUTPUT);
  pinMode(DIR_INNER, OUTPUT);
  digitalWrite(DIR_OUTER, HIGH);
  digitalWrite(DIR_INNER, HIGH);
  Serial.println("Two hands: a minute a second");
}

void loop() {
  minutes++;
  while (outerSteps < minutes * 200 / 60) {
    pulse(STEP_OUTER);
    outerSteps++;
  }
  while (innerSteps < minutes * 200 / 720) {
    pulse(STEP_INNER);
    innerSteps++;
  }
  Serial.print(minutes / 60 % 12);
  Serial.print(":");
  if (minutes % 60 < 10) Serial.print("0");
  Serial.println(minutes % 60);
  delay(1000);
}