int LED = 0;
int POT = 1;
int SW = 3;  //MOSFET
int TRIG = 2; //Switch
 
void setup() {
  // put your setup code here, to run once:
  pinMode(POT, INPUT);
  pinMode(LED, OUTPUT);
  pinMode(SW, OUTPUT);
  pinMode(TRIG, INPUT_PULLUP); 
}
 
void loop() {
  // put your main code here, to run repeatedly:
  if ( digitalRead(TRIG) == LOW) {
    digitalWrite(LED, LOW);
    float v = analogRead(POT);
    analogWrite(SW, v / 1023.0 * 255.0);
    } else {
     analogWrite(SW, 0);
     digitalWrite(LED, HIGH);
    }
}