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CCA Programming & Electronics, Fall 2015

This course repository contains homework assignments, useful guides, and code for "Programming & Electronics" at CCA, Fall 2015.

The syllabus for this course is available in this repository.

Week 1: Wednesday, September 2, 2015


  • Inspirational Videos
  • Introductions
  • What is programming?
  • Goals & course details

Hands-on activities:

  • Human Embodiment of Programmer & Robot
    • Programs generally run line-by-line.
    • While loops, if statements, and functions break that up.


Homework for Week 1

Week 2: Wednesday, September 9, 2015


  • Homework Review


  • Creating sketches with Processing. Write code to create the following sketches in Processing:
  1. one

  2. two

  3. three

  4. four

  5. five

  6. Look through the Processing reference. Pick a function, and use it in a new sketch of your own choosing.

Homework for Week 2

Week 3: Wednesday, September 16, 2015


  • Homework Review: understanding & improving code
  • Objects!

In today's session, we looked at how you might transform a piece of code that shows a ball bouncing around a screen to use classes. Here's a graphic showing what we did, exactly:

bouncing ball with or without classes

In the diagram above, the blue boxes show the modified code; the left side of each blue box pair shows the traditional code, while the right side shows the class-enabled code that achieves the same effect. The red arrows show where inside the Ball class the traditional code goes.

The variables tracking the position, speed, and radius of the ball, as well as the code for drawing and moving the ball, are all put into the class Ball. We say that the variables and functions are "encapsulated" in the Ball class. In Processing, Ball now describes a new type, like int or float, but more complex, a "compound" type. Whenever we create an "instance" of the Ball class, by writing new Ball(), we are creating a new container object that includes its own x, y, vx, vy, and radius variables -- the instance we create contains those 5 other variables. Then the draw and move functions are called on an object, for example, b.move() is the move function of the b object, it only uses and alters the variables inside the b object.

You can create as many instances of a class as you like, giving them different names (for example, Ball b2 = new Ball()) or storing them in arrays. Each will be independent, and calling a function on one object will only affect that one object's variable. The class describes the object, and the instance contains all the data and can have its functions used.

Try it in the homework!

Homework for Week 3

Week 4: Wednesday, September 23, 2015


  • Homework Review: classes
  • Tools for writing code
  • Arrays and ArrayLists

In today's session, we looked at how you can use an ArrayList object to store large numbers of objects. Here's a graphic showing how we went from two Ball objects to 529 Ball objects in a grid:

bouncing balls with or without arraylists

In the diagram above, the blue boxes highlight the changes we made. (Note that the Ball class itself hasn't changed! What's changed is how the code keeps track of the Ball instances we create.)

In the traditional code, each ball needs a new variable (b1 or b2, for example). To display 529 Ball objects in a grid in the traditional way would require creating 529 Ball-type variables -- what a nightmare! Instead, the code creates a new object of type ArrayList<Ball>, called list, that it'll use to keep track of the 529 Ball objects.

You can think of an ArrayList as a new type of variable that can hold many other variables of the same type. For example, ArrayList<Ball> holds Ball objects, but ArrayList<Particle> would only hold Particle objects. If you haven't yet, take a look at the ArrayList reference.

The rest of the code interacts with the ArrayList object in two ways. First, it uses the add function to add Ball objects to the list inside of setup. Then it picks out those objects using from the list using the get function to draw and move them. In setup, two for loops give each Ball object its own x and y position in the grid of balls. In draw, a single for loop to draw() and move() each ball.


Write code to create the following sketches in Processing:

  1. Animated circle drawing


  2. A grid of bouncing circles


Homework for Week 4

Week 5: Wednesday, September 30, 2015


  • What parts do we need to make Pong?


  • Add the following to your Paddle assignment from last week:
    • Modify the balls so they bounce off the paddles
    • Create user control. Two options:
      • Make keys on the keyboard control the paddles, or
      • Make the mouse control one of the paddles
    • Add scoring when balls pass the paddles

Here's one possible set of code that implements the three points above, using keyboard control, based on the techniques covered in class:

class Ball {
  float initialX, initialY;
  float x, y;
  float vx, vy;
  float size = 10;
  color c;

  Ball(float x, float y, color c) {
    this.x = initialX = x;
    this.y = initialY = y;
    this.c = c;
    vx = 2+random(1);
    vy = random(1);

  void draw() {
    ellipse(x, y, size*2, size*2);
  void reset() {
    x = initialX;
    y = initialY;
    vx = 2+random(1);
    if (random(1) < 0.5) {
      vx = -vx;
    vy = random(2) - 1;

  void move() {
    x += vx;
    y += vy;
    if (x < size || x > width-size) {
      vx = -vx;
    if (y < size || y > height-size) {
      vy = -vy;
    if (x-size < leftPaddle.x + leftPaddle.w) {
      if (y > leftPaddle.y &&
          y < leftPaddle.y + leftPaddle.h) {
        vx = -vx;
      } else {
    if (x+size > rightPaddle.x) {
      if (y > rightPaddle.y &&
          y < rightPaddle.y + rightPaddle.h) {
        vx = -vx;
      } else {

class Paddle {
  float x, y;
  float vy;
  float w = 15, h = 80;
  color c;

  Paddle(float x, float y, color c) {
    this.x = x;
    this.y = y;
    this.c = c;
    vy = 0;

  void draw() {
    rect(x, y, w, h);

  void move() {
    y += vy;
    if (y < 0 || y > height-h) {
      vy = 0;
      y = constrain(y, 0, height-h);

ArrayList<Ball> list;
Paddle leftPaddle, rightPaddle;
int leftScore = 0;
int rightScore = 0;

void setup() {
  size(500, 500);
  list = new ArrayList<Ball>();
  list.add(new Ball(width/2, height/2, color(random(255), 255, 255)));

  leftPaddle = new Paddle(15, 150, color(0));
  rightPaddle = new Paddle(width-15-15, 150, color(0));

void drawScores() {
  text(""+leftScore, width/2-30, 40);
  text(""+rightScore, width/2+10, 40);

void draw() {

  for (int i = 0; i < list.size(); i += 1) {


void mousePressed() {
  list.add(new Ball(mouseX, mouseY, color(random(255), 255, 255)));

void keyPressed() {
  if (key == 'q') {
    leftPaddle.vy = -4;
  if (key == 'a') {
    leftPaddle.vy = 4;
  if (key == 'o') {
    rightPaddle.vy = -4;
  if (key == 'l') {
    rightPaddle.vy = 4;

void keyReleased() {
  if (key == 'q' && leftPaddle.vy < 0) {
    leftPaddle.vy = 0;
  if (key == 'a' && leftPaddle.vy > 0) {
    leftPaddle.vy = 0;
  if (key == 'o' && rightPaddle.vy < 0) {
    rightPaddle.vy = 0;
  if (key == 'l' && rightPaddle.vy > 0) {
    rightPaddle.vy = 0;

Extend this code in the homework!

Homework for Week 5

Week 6: Wednesday, October 7, 2015


  • Arduino introduction (slides available in pdf)


  • Building circuits with Arduino and other electronic components!

Homework for Week 6

Week 7: Wednesday, October 14, 2015



  • Start with example AnalogInOutSerial (File > Examples > Analog > AnalogInOutSerial). Here's a simplified version of that code:

    const int analogInPin = A0;  // Analog input pin that the potentiometer is attached to
    const int analogOutPin = 9; // Analog output pin that the LED is attached to
    int sensorValue = 0;        // value read from the pot
    int outputValue = 0;        // value output to the PWM (analog out)
    void setup() {
      // initialize serial communications at 9600 bps:
      pinMode(analogOutPin, OUTPUT);
    void loop() {
      // read the analog in value:
      sensorValue = analogRead(analogInPin);            
      // map it to the range of the analog out:
      outputValue = map(sensorValue, 0, 1023, 0, 255);  
      // change the analog out value:
      analogWrite(analogOutPin, outputValue);           
      // print the results to the serial monitor:
      Serial.print("sensor = " );                       
      Serial.print("\t output = ");      
      // wait 2 milliseconds before the next loop
      // for the analog-to-digital converter to settle
      // after the last reading:

    Make sure you understand what this code does. If not, ask! Here's a schematic of what your circuit should look like:

    potentiometer and LED on pin 9

    Open the serial monitor and see what numbers are printed when you rotate the potentiometer. What's the lowest number you see? Highest?

    1. Modify the code so that instead of changing the brightness of the LED, the Arduino turns on or off the LED (using digitalWrite instead of analogWrite) depending on whether outputValue is greater or less than 127. (Hint: You'll need an if statement. What's the if statement's condition?)

    2. Add 3 more LEDs (4 total) on pins 10, 11, and 12. (Create new variables for the pins they're connected to.) Here's a new schematic: potentiometer and LEDs on pins 9, 10, 11, and 12

    3. Add new if statements so that the 4 LEDs make a "level meter": as you turn the potentiometer from left to right, the LEDs turn on one by one until they're all on when you've turned the potentiometer all the way.

    4. Replace the potentiometer in this circuit with a light-dependent resistor (LDR) in a voltage divider circuit. Here's what you should have:

      LDR and LEDs on pins 9, 10, 11, and 12

      What happens when you cover the LDR?

      Open the serial monitor and see what numbers are printed when you cover and uncover the LDR. What's the lowest number you see? Highest?

    5. Show me your breadboard before moving on.

    6. Replace your LDR with a button. Here's what you should have:

      Button and LEDs on pins 9, 10, 11, and 12

      What happens?

      Open the serial monitor and see what numbers are printed when you push and release the button. What's the lowest number you see? Highest?

      Replace the analogRead function with digitalRead. What happens in the serial monitor now?

  • Use Arduino and Procesing function to create a digital Etch-a-Sketch.

    1. Connect two potentiometers to analog pins A0 and A1. Here's a schematic:

      two potentiometers

    2. Write an Arduino sketch, using the Serial library, that reads the two analog inputs (using analogRead) and prints those values to serial port, two per line, separated by commas. The outputs should look like this in the serial monitor:


      You will likely need both Serial.print and Serial.println. The first number should correspond to the value from pin A0, and the second from pin A1.

    3. Here's a Processing sketch that reads these pairs of numbers from the serial port, and then draws a line from the old coordinate to the new coordinate. But it has a bug! So it doesn't quite work. Fix the bug. (Hint: the bug isn't with the readSerial function!)

      // Etch-a-Sketch
      // based on a sketch by Trevor Shannon
      import processing.serial.*;
      Serial port;
      int oldX = -1;
      int oldY = -1;
      void setup() {
        size(512, 512);
        port = new Serial(this, Serial.list()[Serial.list().length-1], 9600);  
      void drawNextLine(int x, int y) {
        if (oldX >= 0 && oldY >= 0) {
          // draw a line from the old x,y coordinates to the new x,y coordinates
          line(x, y, oldX, oldY);
        // update the "old" x,y coordinates for the next frame
        oldX = x;
        oldY = x;
      void draw() {
        int[] values = readSerial(2);
        if (values != null) {
          drawNextLine(values[0], values[1]);
      void mouseClicked() {
      int[] readSerial(int minValues) {  
        int x; int y;
        String s = port.readStringUntil('\n');
        if (s != null) {
          String[] parts = s.substring(0, s.length()-2).split(",");
          int[] values = new int[parts.length];
          for (int i = 0; i < parts.length; i++) {
            values[i] = int(parts[i]);
          if (values.length < minValues) {
            return null;
          } else {
            return values;
        } else {
          return null;
    4. Replace the potentiometer on pin A1 with a sensing resistor of your choice in a voltage divider -- you can use an LDR like in the previous example, or a force-sensitive resistor, or a thermistor, or... A digital multimeter may help in picking the right corresponding resistor.

    5. Modify the Processing code so that it draws a graph of the value of the second coordinate only (that is, the number that changes when you rotate the potentiometer that you've connected to pin A1).

      You'll need to modify the drawNextLine function so that it doesn't draw a line from x,y to oldX,oldY anymore. Instead, it will use a slowly-increasing x coordinate. Try these two changes:

      1. Create a new variable called columnPosition and use that instead of x in the line function.

      2. Increase columnPosition a little bit on every frame.

    6. Challenge: Also graph the value of the first coordinate!

Homework for Week 7

Week 8: Wednesday, October 21, 2015


  • Homework review
  • More electronics


  • Continuiation of last week's lab; pong with potentiometers.

Homework for Week 8

Week 9: Wednesday, October 28, 2015


  • Practice Quiz review
  • Motors, transistors, and motor drivers.


  • Experiments with motors!
  1. Build the following circuits, one at a time, and observe what happens. Pay particular attention to the speed and strength of the motors. (For the latter two schematics, use the blink sketch or write your own.)

    Motor Circuits

  2. In the third schematic above, you're using the transistor as a digital switch. As we discussed, you can control a motor using 4 switches in this configuration, called an H-Bridge:


  3. Using switches S1, S2, S3, and S4, figure out how to open or close each switch to cause current to flow from left to right through the motor (spinning it "forward") and from right to left through the motor (spinning it "backward"). Make a handy table.

  4. Note that your table never has switches S1 and S3 both closed or S2 and S4 both closed -- why?

  5. That means that the circuit we want is effectively this:

    Two switches

  6. This schematic merges S1 and S3 into a single switch on the left, and S2 and S4 into a single switch on the right. For each switch, there are now three positions: up, down, or "off" (that is, not connected to anything).

  7. This circuit is created for us in the form of a "Half-H Bridge" integrated circuit. We'll use the SN7544 in class -- but there are many others (like the L293D), with the main difference being voltage and current ratings. Here's what it looks like. Note the position of the notch.

    Quad H-bridge

  8. The inputs to the chip are the pins labeled with A, e.g., 1A, 2A, etc. The corresponding outputs (that you connect to your motor) are the pins labeled with Y, e.g., 1Y, 2Y. Send a high voltage on the input pin, and the output pin will be connected to a high voltage -- and similarly with low voltage.

  9. Wire up your motor to one side of the H-bridge.

  10. Write a function in Arduino, void forward(), that spins the motor forward, using pins connected to 1A and 2A

  11. Write an analogous function, void reverse(), for the reverse.

  12. Write an Arduino sketch that uses your two functions to spin the motor forward for 2 seconds, waits for 1 second, then reverses for 1 second.

  13. Add a potentiometer to your sketch -- when rotated one way, the motor should spin in one direction, when rotated the other way, the motor should spin in the other direction. In the middle range, the motor shouldn't spin at all. (What code can you write to stop the motor?)

  14. Add a second motor, connect it to the other half of the integrated circuit.

Homework for Week 9

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