millis(): Non-Blocking Timing

The Problem with delay()

delay() blocks your entire program. While delaying, the Arduino can't:

• Read buttons
• Check sensors
• Update displays
• Do anything else

The millis() Solution

millis() returns the number of milliseconds since the Arduino started. Use it to track elapsed time without blocking.

The Pattern

unsigned long previousMillis = 0;
const long interval = 1000;  // 1 second

void loop() {
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;
    // Do your timed action here
  }

  // Other code runs freely here!
}

Why unsigned long?

millis() returns an unsigned long which overflows after ~49 days. The subtraction pattern (currentMillis - previousMillis) handles overflow correctly. Don't use (currentMillis >= previousMillis + interval).

Multiple Timers

You can have as many independent timers as you want:

unsigned long ledTimer = 0;
unsigned long sensorTimer = 0;

void loop() {
  unsigned long now = millis();

  if (now - ledTimer >= 500) {
    ledTimer = now;
    toggleLED();
  }

  if (now - sensorTimer >= 100) {
    sensorTimer = now;
    readSensors();
  }
}