Blink without delay in Arduino

millis never blocks: compare timestamps instead of sleeping.

// millis never blocks: compare timestamps instead of sleeping.
const unsigned long INTERVAL_MS = 750;

unsigned long lastToggle = 0;
bool ledOn = false;

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  unsigned long now = millis();
  // Subtraction stays correct even when millis wraps around.
  if (now - lastToggle >= INTERVAL_MS) {
    lastToggle = now;
    ledOn = !ledOn;
    digitalWrite(LED_BUILTIN, ledOn ? HIGH : LOW);
  }
}

How it works

1. millis() is the free-running clock since power-on.
2. now - lastToggle >= INTERVAL_MS survives the 49-day wraparound.
3. The loop stays free to do other work between toggles.

Keywords and builtins used here

• HIGH
• LED_BUILTIN
• LOW
• OUTPUT
• bool
• const
• digitalWrite
• false
• if
• long
• loop
• millis
• pinMode
• setup
• unsigned
• void

The run, in numbers

Lines

19

Characters to type

430

Tokens

78

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 72 seconds.

Type this snippet

Step 1 of 3 in Timing, step 10 of 27 in Language basics.

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