Objective: In this activity you'll learn how to use a joystick as a slider to control the brightness of a blue LED.

The Concept of "PWM" Pins: Normal digital pins on an Arduino can only take on/off (high voltage/low voltage) output values. But a few of the digital pins are special PWM pins, which means they can take a range of output values in addition to the regular high/low values. ("PWM" stands for "pulse width modulation.") The PWM values range from 0 to 255. PWM pins are marked with a ~ (tilde) in front of the pin number.

Digital pin 11 is one of these PWM pins. If the LED module is plugged into the Arduino, the blue pin of the LED module is in digital pin 11 of the Arduino.

Using the Joystick as a Slider Control: When moving the joystick forward and backward, or right and left, the joystick value ranges from 0 to 1023. We want to take this value and output it to the blue LED in digital pin 11. Depending on the value, the brightness of the blue LED will vary from full brightness to completely off. 

But there's one other complicating factor we have to take care of to make this work. The joystick value ranges from 0 to 1023. But the range of values for a PWM pin, like digital pin 11, is only 0 to 255. So we have to take the value we get from the joystick and convert it to a brightness value the PWM pin can use. If the joystick value is the max value of 1023, then it needs to be converted to 255, the max value the PWM pin can take. If the joystick value is 0, then the PWM value will be 0. And similarly for all the values in between. 

The conversion formula needed is a proportional equation:

\(brightnessvalue = (joystickvalue)(\frac{255}{1023})\)

We can check the formula to make sure it works. For example, if the joystickvalue is 1023, we see that the brightnessvalue will be 255. And if the joystick value is 0, the brightnessvalue will be 0.

It's also good to check the midpoint value of the range. Using integer values only, the midpoint of 0 to 1023 is 512. Putting that value into the equation gives a brightnessvalue of 127, which is the midpoint of 0 to 255.

The Code:

1. Set up digital pin 11 (the blue LED) for output, and digital pin 2 (the joystick's B pin) and analog pin A0 (the joystick's Y pin) for input. 
2. Start a loop that reads the joystick's B pin until it gets a nonzero "high" or "1" signal, indicating that the joystick button was pushed.
3. Inside the loop :
   1. Get the value of the joystick's Y pin. It will be a value between 0 and 1023.
   2. Convert the Y value to a value between 0 and 255, which will be the brightness value for the blue LED.
   3. Send the brightness value to digital pin 11 (the blue LED) using the analogWrite block.
4. When the loop ends, turn off the LED and print "All done."

Connections (see diagram below):
The joystick has five pins: Y, X, B, VCC, and GND.

1. Using male-to-female wires, connect the VCC and GND pins to the 5V and one of the GND pins, respectively, in the Power section of the Arduino.
2. Connect the B (button) pin to digital pin 2 on the Arduino. Connect the Y pin to analog pin A0. For this activity we don't need the X pin.
3. For the LED module (not shown on the diagram), plug in its B, G, and R pins to digital pins 11, 12, and 13, respectively, on the Arduino, with the module's "-" pin going in the GND pin.