Objective: In this activity you'll expand on the previous "control an LED" activity by learning how to use the forwards-backwards action of a joystick to move a Linkbot robot forward or backward. The code also changes the robot's LED to green when moving forward and red when moving backward.

The code: The pre-placed code blocks set up the digital pins for the LED lights and the joystick's button and the analog pin A0 for the joystick's Y pin. It also initializes a variable named "movingforward" to keep track of when the robot is moving forward (value of 1), stopped (value of 0), and moving backward (value of -1).

As before, the code uses 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. The code then ends. While the loop is running, the code inside the loop uses a conditional "if-elseif-else" statement to check the state of the joystick's Y value.

If the Y value is greater than 712, and if the robot is not already moving forward, it sets the robot speed to positive 4 in/sec and issues a driveForeverNB command (and changes the robot's LED to green).

If the Y value is less than 312, and if the robot is not already moving backward, it sets the speed to -4 in/sec and issues a driveForeverNB command (and changes the robot's LED to red).

Otherwise, it stops the robot and changes the robot's LED to blue (the else clause).

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