Lesson 3: Parking Beeper

/*
  DIY KIT - Arduino Ultrasonic Distance & Parking Learning Kit
  Lesson 3 of 9: Parking Beeper

  WIRING (unplug the USB cable before you wire)
    Keep the sensor and LEDs from Lessons 1-2.
    Active buzzer module, with 3 male-to-female jumper wires:
      I/O (signal, may be labelled S or IN) -> UNO pin 8
      VCC (+)                               -> 5V  (+ rail)
      GND (-)                               -> GND (- rail)

  WHAT SHOULD HAPPEN
    Green  50 cm or more   silent
    Yellow 20 to 49 cm     silent
    Red    10 to 19 cm     slow beeps
    Red    under 10 cm     fast beeps
    No echo: yellow blinks and the buzzer stays silent.
    A tabletop model of a parking sensor - never use it on a real vehicle.
*/

const int RED_LED = 5;
const int YELLOW_LED = 6;
const int GREEN_LED = 7;
const int BUZZER_PIN = 8;
const int TRIG_PIN = 9;
const int ECHO_PIN = 10;

const int CLEAR_CM = 50;      // this far or more: green
const int NEAR_CM = 20;       // closer than this: red + slow beeps
const int CRITICAL_CM = 10;   // closer than this: red + fast beeps

const unsigned long SLOW_ON_MS = 120, SLOW_OFF_MS = 380;   // slow beep
const unsigned long FAST_ON_MS = 100, FAST_OFF_MS = 100;   // fast beep

// Most modules beep when the pin is HIGH. If yours beeps in the gaps or
// all the time, change false to true and upload again.
const bool BUZZER_ACTIVE_LOW = false;

const unsigned long ECHO_TIMEOUT_US = 30000;
const int MIN_CM = 2;
const int MAX_CM = 400;

bool buzzerOn = false;
unsigned long nextBeepChange = 0;

long readOnceCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  unsigned long us = pulseIn(ECHO_PIN, HIGH, ECHO_TIMEOUT_US);
  if (us == 0) return 0;
  long cm = us / 58;
  if (cm < MIN_CM || cm > MAX_CM) return 0;
  return cm;
}

void showLights(bool red, bool yellow, bool green) {
  digitalWrite(RED_LED, red ? HIGH : LOW);
  digitalWrite(YELLOW_LED, yellow ? HIGH : LOW);
  digitalWrite(GREEN_LED, green ? HIGH : LOW);
}

void buzzer(bool on) {
  buzzerOn = on;
  if (BUZZER_ACTIVE_LOW) digitalWrite(BUZZER_PIN, on ? LOW : HIGH);
  else                   digitalWrite(BUZZER_PIN, on ? HIGH : LOW);
}

// Beep with the given on and off times without stopping the program:
// millis() tells us when it is time to switch.
void beep(unsigned long onMs, unsigned long offMs) {
  unsigned long now = millis();
  if (now >= nextBeepChange) {
    buzzer(!buzzerOn);
    nextBeepChange = now + (buzzerOn ? onMs : offMs);
  }
}

void setup() {
  pinMode(RED_LED, OUTPUT);
  pinMode(YELLOW_LED, OUTPUT);
  pinMode(GREEN_LED, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  buzzer(false);
  Serial.begin(9600);
  Serial.println("Lesson 3: Parking Beeper - learning model only");
  Serial.println("cm, zone, buzzer");
}

void loop() {
  long cm = readOnceCm();
  const char *zone;

  if (cm == 0) {
    zone = "NO_ECHO";
    unsigned long halfSeconds = millis() / 500;   // blink yellow, as in Lesson 2
    showLights(false, halfSeconds % 2 == 0, false);
    buzzer(false);                       // unknown: never beep "all clear" or "danger"
  } else if (cm < CRITICAL_CM) {
    zone = "CRITICAL";
    showLights(true, false, false);
    beep(FAST_ON_MS, FAST_OFF_MS);
  } else if (cm < NEAR_CM) {
    zone = "NEAR";
    showLights(true, false, false);
    beep(SLOW_ON_MS, SLOW_OFF_MS);
  } else if (cm < CLEAR_CM) {
    zone = "CAUTION";
    showLights(false, true, false);
    buzzer(false);
  } else {
    zone = "CLEAR";
    showLights(false, false, true);
    buzzer(false);
  }

  Serial.print(cm);
  Serial.print(", ");
  Serial.print(zone);
  Serial.print(", ");
  Serial.println(buzzerOn ? 1 : 0);
  delay(40);
}