due date: Monday, Mar. 15th at the start of class

Image of deflated basketball.

(image from the apparently dearly departed clipart.guru which used to be a family-friendly image sharing site)

In basketball, it’s possible to score one, two, or three points at a time. You and your friends want an easy scorekeeping system which is designed to tally the number of points that your team has.

“If the other team sees this awesome system,” you think, “they will be so intimidated by how clever we are at building things that they’ll become terrible at basketball.”

It’s a foolproof plan.


Your clever scoring system will consist of four buttons (described below), three indicator LEDs, and Serial feedback that specifies the Arduino’s internal timer, the last type of basket made, and the current score.

The buttons should be wired using the INPUT_PULLUP pin mode (which will save you a resistor). Their roles are:

  1. The one point button. When pushed, add one point to the score, announce
    millis = xxxxx, free throw scored, x points
    and light a green LED for two seconds.

  2. The two point button. When pushed, add two points to the score, announce
    millis = xxxxx, field goal scored, x points
    and light a yellow LED for two seconds.

  3. The three point button. When pushed, add three points to the score, announce
    millis = xxxxx, three pointer scored, x points
    and light a red LED for two seconds.

  4. The reset button. This button has a safety feature so you don't trigger a reset accidentally during a game: if the button is not held down for at least one second, it has no effect. As soon as it has been held down continuously for one second, announce
    millis = xxxxx, ----- game reset -----, 0 points
    and change the score to zero. (Holding the button down for longer than one second should not reset the system repeatedly.)


Here is an example interaction, to illustrate the intended outcome: shortly after the Arduino turns on, the user holds down the “reset” button for a bit longer than one second, and the Serial feedback reads:

millis = 2492, ----- game reset -----, 0 points

Then, about 10 seconds after the Arduino turns on, the user pushes the three point button. The red LED lights for two seconds, and the Arduino sends a new line of text so that the complete Serial feedback now reads:

millis = 2492, ----- game reset -----, 0 points
millis = 10284, three pointer scored, 3 points

Note that Serial feedback is only sent when a button is pushed. It is not sent once per second, etc.

If, about 20 seconds after the Arduino was turned on, the user were to then push the two point button: the yellow LED would illuminate for one second, and the Arduino would send one more line of text, so the complete Serial feedback would read:

millis = 2492, ----- game reset -----, 0 points
millis = 10284, three pointer scored, 3 points
millis = 20625, field goal scored, 5 points

A final important note: each button’s LED is supposed to light for two seconds after that button was pushed—but during that time, it’s important that the board is still able to receive a new button push on that, or any different button. This means that you can’t simply use a delay() to keep that LED on—you’ve got to use the chip’s on-board timer, called millis(), to help you out.


Upload the following deliverables to this homework’s Canvas assignment:

1. Video

Please shoot a quick(ish) video with the following things in the following order. You can do it all in one take! (No need to edit separate clips together.) Upload this video to the Canvas assignment.

  1. Press any scoring button so I can see the associated LED until it turns off.
  2. Show the serial feedback on your computer screen.
  3. Press a few buttons in rapid succession (for instance, press the 1-point button, then the 2-point button, then the 3-point, without waiting in between) so I can see the associated LEDs until they turn off.
  4. Show the serial feedback on your computer screen.
  5. Press the reset button briefly (the score should not reset).
  6. Show the serial feedback on your screen. (This way I know the score didn’t reset.)
  7. Hold the reset button for three seconds (the score should reset once).
  8. Show the serial feedback on the screen. (The score should be shown as having reset.)
  9. Have fun with your machine! Press lots of buttons or whatever. Ideally, narrate a sweet basketball game, with a thrilling conclusion. Silliness is encouraged!

2. Photo

Capture a clear image of your breadboard and Arduino so I can see all the wiring clearly enough to compare it with your schematic and make sure they match up. Please try to ensure that the lighting is reasonably clear so I can really see what the wiring is, what resistors you’ve chosen, etc.

3. Technical documentation

  • One image which has a functional block diagram on top and a schematic drawing below, completed using draw.io with the help of the Smart Makerspaces custom parts libraries. Export this as a reasonably high-resolution (1000 pixels wide is fine) .jpg to share.
    • Special update on the custom libraries: go to this link to easily add the block and schematic parts to your draw.io setup. Write Zach if you’re having any trouble with this—it’s in beta but all our testing shows it working properly.
  • Code submission; your file name should have the form andrewID-hw4.ino.

Be sure to include a course-standard comment block at the top of the code you submit, and use good code practice:

  • Select good names for variables, including camelCase names for variables which will change values and ALLCAPS for those which won’t
  • Use the const qualifier for any variable that won’t change, such as pin assignments, e.g. const int BUTTONPIN = 7 or other constants, e.g. const float PI = 3.1416.
  • Add comments as needed to help explain non-obvious things to any future readers


Limited collaboration with your colleagues is permitted. You must build your own circuit and write your own code, but you can talk with other students to get advice and reason through the problem together. You are not permitted to copy anybody else’s code (whether that person is in this class or not). You are permitted to use any internet/book/etc. resource you’d like for guidance, so long as you do not copy code verbatim from such a source. Be sure to list your sources in the “Collaboration” section of your comment block.


points assignment
1 inputs wired properly (and using INPUT_PULLUP configuration)
1 outputs wired properly (with current-limiting resistors)
4 button and LED timing working properly
5 serial feedback (working as described above, and formatted properly)
3 schematic (legible, clean, and valid)
6 code written cleanly, clearly, and with appropriate commenting practice
20 total

A millis() reminder

The Arduino has a built-in timer that begins counting as soon as the board gets power. It counts up in milliseconds, which means the number gets pretty big, pretty quickly. This timer is not affected by a delay() statement or any other thing going on in your code—it’s a very reliable value.

To find out precisely how many milliseconds it’s been since the chip turned on, you simply run the built-in function millis(), which will return the answer. For instance, if you want to find out where millis() is at this moment, simply run


The power of millis() is that by referring to this active timer, you can make things happen on a schedule without using delay() statements. This is a big deal! It means that multiple tasks can run concurrently on their own schedules, without interfering with each other.

See the Blink without blocking section of Code bites for some implementation details.

Using millis() to run a one-second timer: the event-loop model

Here is some minimalistic code which outlines in short form how to use millis() to time a task:

unsigned long timer = 0;

void setup() {}

void loop() {
  // something I want to run every second
  if (millis() - timer >= 1000){    // greater than or equal!
    // this happens once per second
    timer = millis();

Please note that you will need to implement a structure that’s not quite the same as the one shown above in order to get the LEDs to turn off with the correct timing, and a different structure to get your reset button to need to be held down for a second before working. Remember the timing graphs we drew in class to help yourself reason out the logic here!

Help! My buttons keep pressing!

Why do your buttons keep pressing over and over? Because once you’ve gotten rid of the delay()s in your code, those button-press detections are able to run over and over as the loop() keeps executing repeatedly. Part of the challenge of this assignment is solving this problem.

You’ll need to debounce your button presses. There’s a tutorial on that topic featuring example code, but here’s a one-sentence clue of how you might want to approach the problem: instead of detecting the current button state on each loop, detect the state change from unpressed to pressed.


  • Use some global state variables, perhaps like this:
    bool buttonState = true;
    bool lastButtonState = true;
  • Use these variables in your loop to detect when a button transitions from unpressed to pressed
  • Be careful to update the variables at the appropriate times
  • Recall that true and HIGH are synonymous, and false and LOW are as well. (This is somewhat imprecise speech, but it basically holds true in Arduinoland.)
  • Remember that when you’re using INPUT_PULLUP mode, a button will be HIGH until it’s pressed