Talking skull on an Arduino Uno

// Talking skull: a PIR sees a trick-or-treater, the skull's eyes light up and
// its jaw moves in time with a spoken line played by a DFPlayer Mini.
//
//   PIR        VCC -> 5 V   GND -> GND   OUT -> pin 2   (high while it sees movement)
//   jaw servo  PWM -> pin 9, VCC -> 5 V, GND -> GND
//   DFPlayer   VCC -> 5 V   GND -> GND   TX -> pin 10   RX <- 1 k <- pin 11
//              BUSY -> pin 3 (low while a track plays), speaker on SPK_1 and SPK_2
//   eyes       two green LEDs on pins 5 and 6, each through 220 ohms to GND
//
// How the jaw keeps time. There are two honest ways to sync a jaw to a voice.
//
//   1. Follow the audio. Rectify and smooth the speaker signal into an
//      envelope, read it on an analog pin, and open the jaw as far as the
//      voice is loud. Ready-made "audio servo driver" boards do exactly this.
//      It works with any recording, but the jaw chatters on every breath.
//   2. Script it. Listen to the track once, note when each syllable starts,
//      and write those moments down as cues. It takes ten minutes per line and
//      looks crisp, because you decide when the mouth shuts.
//
// This sketch does the second. SCRIPT below is the cue list for track 001:
// "Welcome... to my HAUNTED house! Heh heh heh heh." Each cue says when, in
// milliseconds from the start of the track, the jaw should be at what angle.
// The simulated DFPlayer plays silence, so there is no audio to follow here;
// a scripted jaw moves exactly as it will on the porch.
//
// The track's real end comes from BUSY, not from the script, so a longer
// recording never leaves the jaw hanging open.
//
// On the bench: a PIR needs about a minute after power-up to settle, and
// fires at random until it has. Give the servo its own 5 V supply with its
// ground joined to the Uno's.
//
// Things to try. Click the PIR. Record your own line, time its syllables, and
// replace SCRIPT. Make the eyes flare on the loud syllables: the cue's angle
// is a good stand-in for how loud it is.

#include <SoftwareSerial.h>
#include <DFRobotDFPlayerMini.h>
#include <Servo.h>

const int PIR_PIN = 2;
const int BUSY_PIN = 3;
const int JAW_PIN = 9;
const int EYE_LEFT = 5;
const int EYE_RIGHT = 6;

const int JAW_SHUT = 5;                // degrees
const unsigned long REST_MS = 10000;   // quiet time between visitors

struct Cue {
  uint16_t at;    // ms from the start of the track
  uint8_t angle;  // jaw angle, JAW_SHUT is closed
};

// "Wel-come... to my HAUN-TED house! Heh heh heh heh."
const Cue SCRIPT[] = {
  {0, 30},    {200, 5},   {320, 35},  {560, 5},              // wel-come
  {900, 20},  {1040, 5},  {1120, 25}, {1260, 5},             // to my
  {1450, 45}, {1700, 10}, {1780, 40}, {1980, 5},             // HAUN-TED
  {2100, 35}, {2450, 5},                                     // house!
  {2700, 30}, {2850, 5},  {2950, 30}, {3100, 5},             // heh heh
  {3200, 30}, {3350, 5},  {3450, 30}, {3600, 5},             // heh heh
};
const int CUES = sizeof(SCRIPT) / sizeof(SCRIPT[0]);

SoftwareSerial link(10, 11);           // RX, TX
DFRobotDFPlayerMini player;
Servo jaw;
bool haveSound = false;

bool talking = false;
unsigned long started = 0;
unsigned long quietSince = 0;
int nextCue = 0;
unsigned int visitors = 0;

void eyes(int level) {
  analogWrite(EYE_LEFT, level);
  analogWrite(EYE_RIGHT, level);
}

void speak() {
  talking = true;
  started = millis();
  nextCue = 0;
  eyes(255);
  if (haveSound) player.play(1);
  visitors++;
  Serial.print("Talking to visitor ");
  Serial.println(visitors);
}

void setup() {
  Serial.begin(9600);
  link.begin(9600);
  pinMode(PIR_PIN, INPUT);
  pinMode(BUSY_PIN, INPUT);
  jaw.attach(JAW_PIN);
  jaw.write(JAW_SHUT);
  haveSound = player.begin(link);
  if (haveSound) {
    player.volume(24);
  } else {
    Serial.println("No DFPlayer answered: the skull will mime");
  }
  Serial.println("Skull ready, saying hello once");
  speak();
}

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

  if (talking) {
    unsigned long t = now - started;
    // Play every cue whose moment has come.
    while (nextCue < CUES && t >= SCRIPT[nextCue].at) {
      jaw.write(SCRIPT[nextCue].angle);
      nextCue++;
    }
    // Done when the script is spent and the player says the track is over
    // (BUSY goes high). Without a player, the script alone decides.
    bool playing = haveSound && digitalRead(BUSY_PIN) == LOW;
    if (nextCue >= CUES && !playing && t > 500) {
      talking = false;
      quietSince = now;
      jaw.write(JAW_SHUT);
      eyes(20);
      Serial.println("Done, waiting for the next visitor");
    }
    return;
  }

  if (now - quietSince >= REST_MS && digitalRead(PIR_PIN) == HIGH) {
    speak();
  }
}