Bumper car on an Arduino Uno

// Bumper car: a 2WD chassis on a DRV8833, with two lever microswitches
// mounted on the front corners as bumpers.
//
//   DRV8833  AIN1 pin 5, AIN2 pin 6     left motor
//            BIN1 pin 9, BIN2 pin 10    right motor
//            VM from the four-AA pack (6 V), GND to the Uno's GND
//            SLP left unwired: the breakout pulls it up, so the chip is awake
//   bumpers  COM to GND, NO to pin 7 (left) and pin 8 (right), INPUT_PULLUP
//
// The DRV8833 has two inputs per motor and no enable pin. One input held low
// and a PWM on the other is drive and coast in turn, so the duty is the speed.
// Both low coasts; both high brakes.
//
// A bumper reads LOW while it is pressed, because its NO contact joins the pin
// to ground. The car backs off and turns away from whichever side hit. Hold a
// switch with the mouse to bump the car on the canvas.

const int AIN1 = 5;
const int AIN2 = 6;
const int BIN1 = 9;
const int BIN2 = 10;
const int BUMP_LEFT = 7;
const int BUMP_RIGHT = 8;

const int CRUISE = 180;

// One motor as a signed speed, -255 to 255: PWM on one input, the other low.
void motor(int in1, int in2, int speed) {
  if (speed >= 0) {
    digitalWrite(in2, LOW);
    analogWrite(in1, speed > 255 ? 255 : speed);
  } else {
    digitalWrite(in1, LOW);
    analogWrite(in2, -speed > 255 ? 255 : -speed);
  }
}

void drive(int left, int right) {
  motor(AIN1, AIN2, left);
  motor(BIN1, BIN2, right);
}

void brake() {
  digitalWrite(AIN1, HIGH);
  digitalWrite(AIN2, HIGH);
  digitalWrite(BIN1, HIGH);
  digitalWrite(BIN2, HIGH);
}

void escape(const char *side, int turnLeft, int turnRight) {
  Serial.print("bumped on the ");
  Serial.print(side);
  Serial.println(": back off and turn away");
  brake();
  delay(150);
  drive(-CRUISE, -CRUISE);
  delay(500);
  drive(turnLeft, turnRight);
  delay(400);
}

void setup() {
  pinMode(AIN1, OUTPUT);
  pinMode(AIN2, OUTPUT);
  pinMode(BIN1, OUTPUT);
  pinMode(BIN2, OUTPUT);
  pinMode(BUMP_LEFT, INPUT_PULLUP);
  pinMode(BUMP_RIGHT, INPUT_PULLUP);
  Serial.begin(115200);
  Serial.println("bumper car: ready");
}

void loop() {
  if (digitalRead(BUMP_LEFT) == LOW) {
    escape("left", CRUISE, -CRUISE);
  } else if (digitalRead(BUMP_RIGHT) == LOW) {
    escape("right", -CRUISE, CRUISE);
  } else {
    drive(CRUISE, CRUISE);
  }
  delay(10);
}