Science Olympiad Electric Vehicle code. Target distance is set using 3 rotary dials and progress is counted using a hall effect sensor.

electric_vehicle.ino

long cm; //goal distance
long target; //target # of pulses
volatile long pulses; //current # of pulses
long timer; //time elapsed since start
float conv = 10.208; //cm per 100 pulses
long gatecm = 900; //distance to run before slowing down
long gateTarget; //number of pulses the previous translates to
long dir; //current direction of motion

void setup()
{
    pinMode(4, INPUT_PULLUP); // SW1 bit 0
    pinMode(5, INPUT_PULLUP); // SW1 bit 1
    pinMode(6, INPUT_PULLUP); // SW1 bit 2
    pinMode(7, INPUT_PULLUP); // SW1 bit 3

    pinMode(15, INPUT_PULLUP); // SW2 bit 0
    pinMode(14, INPUT_PULLUP); // SW2 bit 1
    pinMode(8, INPUT_PULLUP); // SW2 bit 2
    pinMode(9, INPUT_PULLUP); // SW2 bit 3

    pinMode(19, INPUT_PULLUP); // SW3 bit 0
    pinMode(18, INPUT_PULLUP); // SW3 bit 1
    pinMode(17, INPUT_PULLUP); // SW3 bit 2
    pinMode(16, INPUT_PULLUP); // SW3 bit 3

    pinMode(2, INPUT_PULLUP);   // encoder
    pinMode(13, INPUT_PULLUP);  // switch
    
    attachInterrupt(0, encoderPinChange, CHANGE);
    
    Serial.begin(115200);
}
void loop() {
    int hun, ten, one, val, i;
  
    // The rotary switch bits are pulled up when open.
    // When closed, they connect to ground, so an "active"
    // bit reads 0/low

  hun = 0;
  hun += digitalRead(4) == 0 ? 100 : 0;
  hun += digitalRead(5) == 0 ? 200 : 0;
  hun += digitalRead(6) == 0 ? 400 : 0;
  hun += digitalRead(7) == 0 ? 800 : 0;

  ten = 0;
  ten += digitalRead(15) == 0 ? 10 : 0;
  ten += digitalRead(14) == 0 ? 20 : 0;
  ten += digitalRead(8) == 0 ? 40 : 0;
  ten += digitalRead(9) == 0 ? 80 : 0;

  one = 0;
  one += digitalRead(19) == 0 ? 1 : 0;
  one += digitalRead(18) == 0 ? 2 : 0;
  one += digitalRead(17) == 0 ? 4 : 0;
  one += digitalRead(16) == 0 ? 8 : 0;
  
  cm = hun + ten + one; //read target value from dials
  target = (cm * 100L) / conv; //calculate needed pulses until target
  gateTarget = (gatecm * 100L) / conv; //calculate needed pulses until gate

  while (digitalRead(13) == 1); //wait for switch to be pressed
  delay(10); //wait to  avoid bouncing
  pulses = 0; //reset encoder
  timer = millis(); //set time out count
  dir = 1;
  analogWrite(10, 230);
  analogWrite(11, 0);
  while (pulses <= gateTarget && digitalRead(13) == 0 && millis() <= timer + 10000); //encoder count to 9 meters or time out if never reached
  analogWrite(10, 0);
  analogWrite(11, 0);
  delay(10); //wait to dissipate field
  analogWrite(10,0);
  analogWrite(11, 230);
  delay(1000);
  analogWrite(10, 0);
  analogWrite(11, 100); //turn on brakes
  delay(2000); //wait to finish coast
  analogWrite(11, 0);
  analogWrite(11, 50); //turn on brakes
  delay(2000); //wait to finish coast
  
  if (pulses < target) { //if we have yet to reach it,
    timer = millis(); //reset time out baseline
    dir = 1;
    analogWrite(10, 120); //motor creep in original direction
    analogWrite(11, 0);  //motor still off in other direction
    while (pulses < target && digitalRead(13) == 0 && millis() <= timer + 10000); //encoder count to target
    analogWrite(11, 0);
    analogWrite(10, 0);
    delay(10); //wait to dissipate EM field
    analogWrite(10, 0);
    analogWrite(11, 30); //turn on brakes
    delay(3000); //wait to finish coast
  }
  analogWrite(10, 0); //turn off
  analogWrite(11, 0); //motor completely
  while (digitalRead(13) == 0) //wait for switch to be flipped back up
    Serial.println(pulses);
}

void encoderPinChange() {
  pulses += dir;
}