/*
 * car.ino — Arduino Bluetooth: Make It Connect, chapter 9
 *
 * A Bluetooth-driven two-motor car. Command handling from chapter 8, motion
 * from chapter 9.
 *
 * PINS — these match the real car this book is drawn from.
 *
 *   ENA  5   ENB  6      <- MUST be PWM pins. On an Uno that is 3, 5, 6, 9, 10, 11.
 *   IN1 12   IN3 10
 *   IN2 11   IN4  9
 *
 * ⚠️ The enables are the trap. analogWrite() only produces PWM on pins that
 * have the hardware for it. Anywhere else it silently degrades to a digital
 * write — above 127 is HIGH, below is LOW — so the car drives perfectly at
 * exactly one speed and never reports an error. The car this book is drawn
 * from had its enables on pins 13 and 8 for ten years and nobody noticed the
 * speed control had never once worked.
 *
 * ⚠️ Also pull the jumper caps off the L298N's ENA/ENB headers. Fitted, they
 * tie the enables to +5V and override the Arduino entirely — same one-speed
 * symptom, different cause.
 *
 * POWER — battery + to the L298N's +12V AND to the Arduino's Vin.
 *         battery - to the L298N's GND AND the Arduino's GND.
 * The Arduino needs feeding too; this is the step people miss.
 *
 * The Bluetooth module goes on pins 2 and 3 here, leaving the hardware serial
 * port free so you can watch what arrives while the car is connected.
 *   Module TXD -> pin 2
 *   Module RXD -> pin 3, through the 1k/2k divider
 *
 * troniction.com/code/
 */

#include <SoftwareSerial.h>

SoftwareSerial bt(2, 3);   // RX, TX — from the Arduino's point of view

const int ENA = 5,  IN1 = 12, IN2 = 11;
const int ENB = 6,  IN3 = 10, IN4 = 9;

int speed = 200;           // 0-255. 'S' stops; '0'-'9' set this.

void setup() {
  pinMode(ENA, OUTPUT); pinMode(IN1, OUTPUT); pinMode(IN2, OUTPUT);
  pinMode(ENB, OUTPUT); pinMode(IN3, OUTPUT); pinMode(IN4, OUTPUT);

  Serial.begin(9600);
  bt.begin(9600);
  halt();
  Serial.println(F("Car ready. F B L R S, or 0-9 for speed."));
}

// ---- motion ---------------------------------------------------------------
// Which way is "forward" depends on how the motors are mounted and wired. If a
// wheel turns the wrong way, swap that motor's two wires at the terminal block
// or swap its two pins here. Both are correct fixes — test it, don't reason
// about it.

void drive(bool aFwd, bool bFwd) {
  digitalWrite(IN1, aFwd ? HIGH : LOW);
  digitalWrite(IN2, aFwd ? LOW  : HIGH);
  digitalWrite(IN3, bFwd ? HIGH : LOW);
  digitalWrite(IN4, bFwd ? LOW  : HIGH);
  analogWrite(ENA, speed);
  analogWrite(ENB, speed);
}

void forward()  { drive(true,  true);  }
void backward() { drive(false, false); }
void left()     { drive(false, true);  }   // one side reverses to turn on the spot
void right()    { drive(true,  false); }

void halt() {
  analogWrite(ENA, 0);
  analogWrite(ENB, 0);
  digitalWrite(IN1, LOW); digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW); digitalWrite(IN4, LOW);
}

// ---- commands -------------------------------------------------------------
void loop() {
  if (!bt.available()) return;

  char c = bt.read();

  if (c >= '0' && c <= '9') {
    // Map 0-9 onto the usable part of the range. Below about 60 most cheap
    // gear motors will not start turning at all, so 0 is stop and 1 is the
    // slowest speed that actually moves.
    speed = (c == '0') ? 0 : map(c - '0', 1, 9, 60, 255);
    Serial.print(F("speed ")); Serial.println(speed);
    if (speed == 0) halt();
    return;
  }

  switch (c) {
    case 'F': forward();  break;
    case 'B': backward(); break;
    case 'L': left();     break;
    case 'R': right();    break;
    case 'S': halt();     break;
    default:  break;
  }
}