Joystick robot car with an L298N on an Arduino Uno

// Joystick robot car: a thumb stick steers a 2WD chassis on an L298N, the way
// a tank is driven. Push up to go, sideways to turn, up and sideways to curve.
//
//   Joystick  SW -> A0 (INPUT_PULLUP), VRY -> A1, VRX -> A2
//             VCC -> the L298N's 5V terminal, GND
//   L298N     ENA pin 5, IN1 pin 6, IN2 pin 7    left motor (ENA jumper off)
//             ENB pin 10, IN3 pin 8, IN4 pin 9   right motor (ENB jumper off)
//             12V from the 7.4 V pack, GND to the Uno's GND
//
// The stick is two potentiometers, so each axis reads 0 to 1023 with the
// middle about 512. Pushed up, VRY falls toward 0; pushed right, VRX rises
// toward 1023. The sketch turns them into a throttle and a steer from -255
// to 255, then mixes them into the two wheels:
//
//   left  = throttle + steer
//   right = throttle - steer
//
// Full right with no throttle spins the car on the spot. A real stick never
// rests exactly on 512, so anything within DEAD of the middle counts as
// centered, or the car creeps. Press the stick to toggle a slow mode at half
// speed, for tight spaces.
//
// Press Run, then drag the stick's cap.

const int ENA = 5;
const int IN1 = 6;
const int IN2 = 7;
const int ENB = 10;
const int IN3 = 8;
const int IN4 = 9;

const int STICK_SW = A0;  // an analog pin works as a digital input
const int STICK_Y = A1;
const int STICK_X = A2;

const int DEAD = 40;

bool slow = false;
bool wasPressed = false;
int lastLeft = 999;
int lastRight = 999;

// One side of the car, as a signed speed from -255 to 255. Zero brakes.
void side(int en, int a, int b, int s) {
  digitalWrite(a, s > 0 ? HIGH : LOW);
  digitalWrite(b, s < 0 ? HIGH : LOW);
  if (s < 0) s = -s;
  analogWrite(en, s == 0 ? 255 : s);
}

// One axis from 0..1023 to -255..255, with the dead band in the middle.
int axis(int reading) {
  int offset = reading - 512;
  if (abs(offset) <= DEAD) return 0;
  int s = map(abs(offset), DEAD, 511, 0, 255);
  if (s > 255) s = 255;
  return offset > 0 ? s : -s;
}

void setup() {
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
  pinMode(IN3, OUTPUT);
  pinMode(IN4, OUTPUT);
  pinMode(STICK_SW, INPUT_PULLUP);
  Serial.begin(9600);
  Serial.println("Joystick car: push up to drive, sideways to turn, press for slow");
}

void loop() {
  bool pressed = digitalRead(STICK_SW) == LOW;
  if (pressed && !wasPressed) {
    slow = !slow;
    Serial.println(slow ? "slow mode" : "full speed");
  }
  wasPressed = pressed;

  int throttle = -axis(analogRead(STICK_Y));  // up is forward
  int steer = axis(analogRead(STICK_X));
  int left = constrain(throttle + steer, -255, 255);
  int right = constrain(throttle - steer, -255, 255);
  if (slow) {
    left /= 2;
    right /= 2;
  }
  side(ENA, IN1, IN2, left);
  side(ENB, IN3, IN4, right);

  if (abs(left - lastLeft) > 8 || abs(right - lastRight) > 8) {
    lastLeft = left;
    lastRight = right;
    Serial.print("left ");
    Serial.print(left);
    Serial.print("  right ");
    Serial.println(right);
  }
  delay(20);
}