car.c

int led = 7
byte brightness = 20
int detect = 9
int bright_max = 255
int bright_min = 20

const CLOSED = LOW;
const OPEN = HIGH;

pinMode(led, OUTPUT);
pinMode(detect, INPUT);

void setup(){

}

void loop() {
    if (digitalRead(detect) == LOW && brightness > bright_min) {
        brightness--;
        analogWrite(led, brightness);
        delay(10);
    } else if (digitalRead(detect) == HIGH && brightness < bright_max) {
        brightness++;
        analogWrite(led, brightness);
        delay(10);
    }
}