int pwmPin = 11;  // The Arduino can turn on and off pwn fast.
// This can make LED appear dimmer, and motors turn slower.
// This depends how much they are 'on' and 'off.'
// Only pins 3,5,6,9,10,11 can do this. They are shown with a '~' on the Arduino.

int potPin = 19;   // Pin A5 is the same as pin 19. This matches the ThinkerShield location.
// A Potentiometer or LDR can be used for analog inputs.
// The LDR on the ThinkerShield is at A4.
int ldrPin = A4;


void setup() {
  Serial.begin(9600);
  pinMode(pwmPin, OUTPUT);
  pinMode(potPin, INPUT);
  pinMode(ldrPin, INPUT);

}//EOS

// This loop reads the 2 values, calculated the difference, coverts to 8bit, and dims the LED.

void loop() {
  // The analog value 0-1023 is saved to this variable.
  int potentiometerValue = analogRead(potPin);
  int ldrValue = analogRead(ldrPin);
  
  int pot_Minus_ldr = abs(potentiometerValue - ldrValue);
  
  // The analog value is 'mapped' to the 8bit values (0-255).
  // 0 is LOW. 255 is HIGH. 128 is 50%.
  int pwmValue = map (pot_Minus_ldr, 0, 1023, 0, 255);
  
  //The values are sent to the Serial Monitor.
  Serial.println((String)"Potentiometer Value:" + potentiometerValue + " LDR Value: " +  ldrValue + " Difference: " + pot_Minus_ldr +  " PWM Value: " + pwmValue );

  // analogWrite is used instead of digitalWrite.
  analogWrite(pwmPin, pwmValue);

  // the delay command stops the Arduino working ridiculously fast. 
  // Your loop should always contain at least one delay.
  delay (500);

} //EOL