I made a Vetinari Clock

[rdmiller3]

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/*
* vetinariclock - an unsettling timepiece driver for Arduino
*
* Copyleft (GPL) Rick Miller 2010-09-12
*/

const int pinA = 2;
const int pinB = 3;

void setup() {
pinMode(pinA, OUTPUT);
pinMode(pinB, OUTPUT);
digitalWrite(pinA, LOW);
digitalWrite(pinB, LOW);
}

void loop() {
watchTime();
}

unsigned long lastTick = 0;
unsigned long nextTick = 1000;

const int minInterval = 250;
const int maxInterval = 1750;
int ahead = 0;

void watchTime()
{
unsigned long now = millis();
int i;

if ((now > nextTick) &&
((now - nextTick) < 10000)) // in case nextTick rolled over
{
lastTick = nextTick;
if (ahead < (-5000))
{
i = minInterval;
}
else if (ahead > 5000)
{
i = 2000;
}
else
{
i = random(minInterval, maxInterval);
}
nextTick += i;
ahead += (1000 - i);
tick();
}
}

void tick()
{
static boolean polarity = false;

int pin = (polarity ? pinA : pinB);

digitalWrite(pin, HIGH);
delay(100);
digitalWrite(pin, LOW);

polarity = (! polarity);
}