Tinkerbot 3.6.1: Controlling brightness of LED with proximity sensor

Tinkerbot 3.6.1

#include <NewPing.h>

const int ULTRASONIC_TRIGGER = 6;
const int ULTRASONIC_ECHO = 7;
const int LED_PIN = 11;

#define MAX_DISTANCE 100

NewPing sonar(ULTRASONIC_TRIGGER, ULTRASONIC_ECHO, MAX_DISTANCE);

void setup() {
  pinMode(ULTRASONIC_TRIGGER, OUTPUT);
  pinMode(ULTRASONIC_ECHO, INPUT);
  
  pinMode(LED_PIN, OUTPUT);
  
  Serial.begin(9600);
}

void loop() {
 
  int distance = sonar.ping_cm();
  // If distance value is 0, it means that the object is very far away
  if (distance == 0) {
    distance = MAX_DISTANCE;
  }
  // We are only interested in the 10cm to 20cm range, so we constrain
  // it to that range, and then map it to the brightness value (inverse map)
  distance = constrain(distance, 10, 20);
  int brightness = map(distance, 10, 20, 128, 0);
  
  // brightness should be a value between 0 and 255
  analogWrite(LED_PIN, brightness);
  Serial.print(distance);
  Serial.print(", ");
  Serial.println(brightness);
  delay(5);
}