a calming blinking light — https://caffo.link/led

calming.c

const int ledPin = 13;
unsigned long startTime;
float currentDelay;
float initialBPM;
float finalBPM;
unsigned long interval;      // Duration of BPM change
unsigned long holdInterval;  // Duration to hold at final BPM
unsigned long fadeInterval;  // Duration of fade to off
unsigned long totalTime;     // Total time until LED turns off

// Function to convert minutes to milliseconds
unsigned long minutesToInterval(float minutes) {
  return minutes * 60 * 1000;
}

void setup() {
  pinMode(ledPin, OUTPUT);
  startTime = millis();  // Record the start time

  // Set your desired BPM and intervals here
  initialBPM = 220.0;    // Starting BPM
  finalBPM = 60.0;       // Final BPM
  interval = minutesToInterval(20);     // Duration of BPM change (20 minutes)
  holdInterval = minutesToInterval(20); // Hold at final BPM (20 minutes)
  fadeInterval = minutesToInterval(30); // Fade duration (30 minutes)
  totalTime = interval + holdInterval + fadeInterval;  // Total duration

  // Calculate the initial delay in milliseconds
  currentDelay = 60000.0 / initialBPM;  // 60,000 milliseconds in a minute
}

void loop() {
  unsigned long currentTime = millis();
  unsigned long elapsedTime = currentTime - startTime;

  if (elapsedTime < interval) {
    // Gradually change BPM
    float intervalFraction = (float)elapsedTime / interval;
    float bpm = initialBPM + (finalBPM - initialBPM) * intervalFraction;
    currentDelay = 60000.0 / bpm;
  } else if (elapsedTime < interval + holdInterval) {
    // Hold at final BPM
    currentDelay = 60000.0 / finalBPM;
  } else if (elapsedTime < totalTime) {
    // Fading logic will be added here later
  } else {
    // Turn off LED after total duration
    digitalWrite(ledPin, LOW);
    return; // Stop the loop
  }

  // Blink the LED
  digitalWrite(ledPin, HIGH);
  delay((int)currentDelay);
  digitalWrite(ledPin, LOW);
  delay((int)currentDelay);
}