const byte brocheEcho = 10;
const byte brocheTrig = 11;
const byte brocheBuzz = 5;
const byte brocheLed = 4;

const unsigned int distanceSeuil = 50;  // cm
const unsigned int deltaSeuil = 5;      // cm

const unsigned long dureeBuzz = 1000;   // ms
unsigned long chronoDebutBuzz;


enum {REPOS, ACTIVATION, ACTIF} etat = REPOS;

unsigned long distance() {
  static unsigned long d;
  const unsigned long periodeMesure = 100; // en ms => 10Hz (min 29ms entre 2 pings)
  unsigned long chronoDerniereMesure = -periodeMesure;
  if (millis() - chronoDerniereMesure >= periodeMesure) {
    digitalWrite(brocheTrig, HIGH);
    delayMicroseconds(10);
    digitalWrite(brocheTrig, LOW);
    d = pulseIn(brocheEcho, HIGH) / 58;
    chronoDerniereMesure = millis();
  }
  return d;
}

void setup() {
  pinMode(brocheBuzz, OUTPUT);
  pinMode(brocheLed, OUTPUT);
  pinMode(brocheTrig, OUTPUT);
  pinMode(brocheEcho, INPUT);
}

void loop() {
  switch (etat) {
    case REPOS:
      if (distance() < distanceSeuil) {
        chronoDebutBuzz = millis();
        tone(brocheBuzz, 500);
        digitalWrite(brocheLed, HIGH);
        etat = ACTIVATION;
      }
      break;

    case ACTIVATION:
      if (millis() - chronoDebutBuzz >= dureeBuzz) {
        noTone(brocheBuzz);
        etat = ACTIF;
      } else {
        if (distance() >= distanceSeuil + deltaSeuil) {
          noTone(brocheBuzz);
          digitalWrite(brocheLed, LOW);
          etat = REPOS;
        }
      }
      break;

    case ACTIF:
      if (distance() >= distanceSeuil + deltaSeuil) {
        digitalWrite(brocheLed, LOW);
        etat = REPOS;
      }
      break;
  }
}