Huggables

// Author: Jawad Farooq Naik
// Date Created: April 18, 2025, 10:00 AM EDT
// Location: Boston, MA, USA
// Project: Huggables
// Institution: Massachusetts College of Art and Design
// Department: Dynamic Media Institute
// Project Description:
// Huggables is an interactive project designed to bridge the emotional gap in long-distance relationships.
// It consists of a set of interconnected body pillows that mimic the sensation of hugging a human.
// When one partner’s pillow detects a pulse, the other partner’s pillow immediately actuates—and vice versa.
// The system synchronizes a rhythmic heartbeat, gentle breathing motion, soothing warmth (temperature), and a familiar scent,
// recreating the comforting presence of a real embrace across both pillows.

// —— Library Includes —— 
#include <Servo.h>
#include <PulseSensorPlayground.h>

// —— Pin Assignments —— 
constexpr int PULSE_PIN        = A0;   // PulseSensor → A0
constexpr int BLINK_LED_PIN    = 13;   // Optional LED that blinks on each beat
constexpr int HEART_SERVO_PIN  = 3;    // Heartbeat servo → D3
constexpr int BREATH_SERVO_PIN = 9;    // Breathing servo → D9

// —— Timing Constants —— 
constexpr unsigned long MIN_INTERVAL     = 300;   // Minimum ms between beats (refractory, ≲200 BPM)
constexpr unsigned long IDLE_TIMEOUT     = 2000;  // ms after last beat before idling
constexpr unsigned long BREATH_PHASE_MS  = 500;   // ms per inhale/exhale phase

// —— Global Objects —— 
PulseSensorPlayground pulseSensor; 
Servo                 heartServo, breathServo;

// —— State Variables —— 
unsigned long lastBeatMillis    = 0;    // Timestamp of last detected beat
unsigned long lastBreathMillis  = 0;    // Tracks timing for breathing cycle
byte          breathPhase       = 0;    // 0=inhale,1=neutral,2=exhale,3=neutral
bool          wasActive         = false;// Tracks idle→active transitions

// —— Setup() ——
// Initializes serial port, pulse sensor, and servos.
void setup() {
  Serial.begin(115200);

  // PulseSensorPlayground configuration
  pulseSensor.analogInput(PULSE_PIN);
  pulseSensor.blinkOnPulse(BLINK_LED_PIN);  // Optional LED feedback
  pulseSensor.setThreshold(550);            // Tune threshold between idle/beat
  if (!pulseSensor.begin()) {
    Serial.println("PulseSensor not detected. Check wiring!");
  }

  // Attach and center servos
  heartServo.attach(HEART_SERVO_PIN);
  breathServo.attach(BREATH_SERVO_PIN);
  heartServo.write(90);
  breathServo.write(90);
}

// —— loop() ——
// 1. Detect heartbeats via pulseSensor.sawStartOfBeat()
// 2. On each beat: drive heartbeat servo and mark timestamp
// 3. Determine active state (finger present) vs idle
// 4. On idle→active edge: reset breathing cycle
// 5. While active: run breathing state machine
// 6. When idle: snap servos back to neutral
void loop() {
  unsigned long now = millis();

  // —— 1) HEARTBEAT DETECTION ————————————————————————————————————————————
  if (pulseSensor.sawStartOfBeat()) {
    // Drive heartbeat servo: contract, relax, then neutral
    heartServo.write(100);  // contraction
    delay(120);
    heartServo.write(80);   // relaxation
    delay(120);
    heartServo.write(90);   // neutral

    lastBeatMillis = now;   // record beat time
    Serial.println("Beat!");
  }

  // —— 2) ACTIVE vs IDLE STATE —————————————————————————————————————————
  bool active = (now - lastBeatMillis) < IDLE_TIMEOUT;

  // —— 3) IDLE→ACTIVE EDGE: INITIALIZE BREATHING ————————————————————————
  if (active && !wasActive) {
    breathPhase      = 0;      // start at inhale
    lastBreathMillis = now;
    breathServo.write(100);    // set to inhale position immediately
  }
  wasActive = active;

  // —— 4) BREATHING CYCLE (ONLY WHEN ACTIVE) ———————————————————————————
  if (active) {
    if (now - lastBreathMillis >= BREATH_PHASE_MS) {
      // Advance to next phase: 0→1→2→3→0…
      breathPhase = (breathPhase + 1) & 0x03;
      lastBreathMillis = now;
      switch (breathPhase) {
        case 0: breathServo.write(100); break;  // inhale
        case 1: breathServo.write(90);  break;  // neutral
        case 2: breathServo.write(80);  break;  // exhale
        case 3: breathServo.write(90);  break;  // neutral
      }
    }
  }
  // —— 5) SNAP TO NEUTRAL WHEN IDLE ———————————————————————————————————
  else {
    heartServo.write(90);
    breathServo.write(90);
  }
}