#include <Wire.h>

#define PIN_LED       3

int potValue = 0;

void setup() {
  pinMode(PIN_LED, OUTPUT);
  
  Wire.begin();
}

void loop() {
  potValue = analogRead(A0);
  potValue = map(potValue, 0, 1023, 0, 255);

  Wire.beginTransmission(42);
  Wire.write(potValue);
  Wire.endTransmission();

  analogWrite(PIN_LED, potValue);
}