int potPin = A5;
int potRead = 0;
int ledPin = D2;
int ledBright = 0;
int switchPin = D3;

void setup() {
    pinMode(ledPin, OUTPUT);
    pinMode(switchPin, INPUT_PULLUP);
    Particle.variable("pot", potRead);
    Particle.variable("led", ledBright);
}

void loop() {
    int switchStatus = digitalRead(switchPin);
    if (switchStatus == LOW){ // if turning on the switch
        potRead = analogRead(potPin);
        // change the range of potRead
        ledBright = map(potRead, 0, 4095, 0, 255);
        analogWrite(ledPin, ledBright);
    }else{ // if turning off the switch
        digitalWrite(ledPin, LOW);
    }
}