Lesson 7: Parking Assistant & Sensor Dashboard

/*
  DIY KIT - Arduino UNO Sensor & Output Starter Kit
  Lesson 7 of 7: Parking Assistant & Sensor Dashboard (uses every part)

  PIN PLAN - the same pins as Lessons 1-6, so nothing moves:
    Red LED    -> 220 ohm -> pin 2      Yellow LED -> 220 ohm -> pin 3
    Green LED  -> 220 ohm -> pin 4      (LED short legs -> GND)
    Servo signal (orange) -> pin 5      Buzzer S -> pin 6
    HC-SR04 TRIG -> pin 8, ECHO -> pin 9
    LCD RS 12, E 11, D4 10, D5 7, D6 A1, D7 A2; VO -> potentiometer middle pin

  SERVO POWER (ask an adult): the servo's red wire goes to a SEPARATE
  regulated 5 V supply, its brown wire to GND, and that supply's GND joins
  the UNO GND. Never join the supply's + to the UNO 5V pin.
  No supply? Leave the servo unplugged - everything else still works.

  WHAT SHOULD HAPPEN (hold a book in front of the sensor)
    25 cm or more : green LED          10-24 cm : yellow LED
    under 10 cm   : red LED + buzzer   LCD shows the distance and servo angle,
    and the servo arm swings like a gauge between about 5 and 50 cm.
*/

#include <Servo.h>
#include <LiquidCrystal.h>

const int RED_LED    = 2;
const int YELLOW_LED = 3;
const int GREEN_LED  = 4;
const int SERVO_PIN  = 5;
const int BUZZER_PIN = 6;
const int TRIG_PIN   = 8;
const int ECHO_PIN   = 9;

const long NEAR_CM = 10;   // closer than this: red LED + buzzer
const long SLOW_CM = 25;   // closer than this: yellow LED
const bool BUZZER_ACTIVE_LOW = false;   // same setting as Lesson 3

LiquidCrystal lcd(12, 11, 10, 7, A1, A2);   // RS, E, D4, D5, D6, D7
Servo gauge;

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

// Distance in cm, or -1 when no echo comes back (nothing in range).
long readDistanceCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  long us = pulseIn(ECHO_PIN, HIGH, 30000);
  if (us == 0) return -1;
  return us / 58;
}

// Light exactly one LED for the zone - or none when there is no reading.
void showZone(long cm) {
  bool valid = cm > 0;
  digitalWrite(RED_LED,    valid && cm < NEAR_CM);
  digitalWrite(YELLOW_LED, valid && cm >= NEAR_CM && cm < SLOW_CM);
  digitalWrite(GREEN_LED,  valid && cm >= SLOW_CM);
  buzzer(valid && cm < NEAR_CM);
}

// 5 cm -> 170 degrees ... 50 cm -> 20 degrees. No reading -> middle (90).
int gaugeAngle(long cm) {
  if (cm < 0) return 90;
  cm = constrain(cm, 5, 50);
  return map(cm, 5, 50, 170, 20);
}

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);

  lcd.begin(16, 2);
  lcd.print("Parking Assist");
  gauge.attach(SERVO_PIN);
  gauge.write(90);

  Serial.begin(9600);
  Serial.println("Lesson 7: Parking Assistant & Sensor Dashboard");
  delay(1000);
  lcd.clear();
}

void loop() {
  long cm = readDistanceCm();
  int angle = gaugeAngle(cm);

  showZone(cm);
  gauge.write(angle);

  lcd.setCursor(0, 0);
  lcd.print("Dist: ");
  if (cm < 0) {
    lcd.print("--      ");
  } else {
    lcd.print(cm);
    lcd.print(" cm    ");   // spaces wipe old digits
  }
  lcd.setCursor(0, 1);
  lcd.print("Servo: ");
  lcd.print(angle);
  lcd.print(" deg  ");

  Serial.print("dist_cm:");
  Serial.print(cm);
  Serial.print(",servo_deg:");
  Serial.println(angle);

  delay(200);
}