Game 2: Rock, paper, scissors over the radio

Chapter 7 image


Let’s play a game of rock, paper, scissors! Rock, paper and scissors is a game played with two players. Each player, at the same time, forms one of the three shapes (rock, paper or scissor) with their hands. Then, they use these rules to decide who wins:

  • The rock crushes the scissors.

  • The scissors cuts the paper.

  • The paper covers the rock.

  • If both players choose the same shape, it is a tie.

Figure below shows these rules.

Rock paper scissors game: Rock beats Scissors. Scissors beats Paper. Paper beats Rock.

Figure 1: Rock paper scissors game: Rock beats Scissors. Scissors beats Paper. Paper beats Rock

In this chapter, you will program this game using your micro:bits. Doing so, you will practice:

  • Unicast communication

  • Programming with variables

  • Programming with conditionals

What you’ll need

2 micro:bits
1 whiteboard/board
boardmarkers/postit notes
1 teammate

Programming: Rock, paper, scissors

To program this game, it is best to work with a teammate. Task 1 is for familiarising you with the game and will not use the radio. Starting from Task 2, you will start writing the parts of your program to play this game over the radio.

Task 1: Start with the simple game

Description: To familiarize yourself with the game, try the Rock-Paper-Scissors activity. Notice that the program gives a number to rock, paper and scissors. For example, paper=1, rock=2, and scissors=3.

Instruction: Program the code shown on the Rock-Paper-Scissors activity page, and download it to your micro:bits. Play the game with a friend. You will each shake your micro:bits at the same time and then decide who wins using the games rules as described above.

Task 2: Hand shapes over the radio with unicast

Description: To play the game over the radio, you will use the button A to select paper, rock or scissors. You will use button B to confirm your selection and send it over the radio. Like in Task 1, use paper=0, rock=1, scissors=2.

Instruction: Write a program to do the following:

  1. Use button A to select paper, rock or scissors. Each time you press button A, it should alternately show an icon of either paper, rock or scissors.

  2. Use button B to confirm your selection, and unicast it to your friend’s micro:bit over the radio like you did in Unicast Communication: One to One.

  3. Add code for receiving a number. When you receive a number, show the corresponding icon on the display. For example, if you received 0, display the paper icon.

Test with your teammate that you can send and receive your hand shape values over the radio.

Task 3: Fill the table of rules

Description: Your program, when it receives a number from your teammate’s micro:bit, decides who wins.

Instruction: To decide who wins, compare the number you picked with the number you received. We provided an incomplete table below to help you decide the result [^2]. Using this table, you compare My hand to Opponent's hand. For example, if both of these numbers mean Paper, it is a tie, and the result is a surprised face. But, if My hand is for Paper and the Opponent's hand is for Scissors, the result is a sad face. In contrast, if My hand is for Scissors and the Opponent's hand is for Paper, then the result is a happy face. Using the rules of the game, fill the rest of the table.

Rock paper scissors table<

Figure 2: Incomplete rock, paper, scissors table

Task 4: Play the game

Description: Once you filled the table, you need to decide how to program these rules in your code. Your program will:

  1. play the game based on Rock-Paper-Scissors rules

  2. display a happy face if you won, a sad face if you lost. And if it’s a draw, show a surprised face.

Instruction: Figure below shows a template for programming the table using the if block in the JavaScript Blocks editor Logic menu. Note that this is just a template and it is there to give you an idea of the structure of your program. For instance, your on radio received block will have to be different to do unicast communication (see Unicast Communication: One to One).

You will notice in the template that we used two variables: selected and received. selected is set to True when you make the selection for your hand by pressing button B. received is set to True when you receive your opponent’s hand. In the forever block, the game is only played when both selected and received are True. Once you enter the block to play the game, these variables are initialized to False for the next round.

After you program the game, play it with your teammate! Who wins more often?

let my_hand = 0
let selected = false
input.onButtonPressed(Button.B, function () {
    selected = true
let opponent_hand = 0
let received = false
radio.onReceivedNumber(function (receivedNumber) {
    received = true
    opponent_hand = receivedNumber
let my_hand = 0
let opponent_hand = 0
let received = false
let selected = false
basic.forever(function () {
    if (selected == true && received == true) {
        selected = false
        received = false
        if (opponent_hand == my_hand) {
        } else {
            if (my_hand == 0 && opponent_hand == 1) {
            } else if (0 == 0) {

            } else if (0 == 0) {

            } else {


Figure 3: Rock paper scissors: A template for programming the rules


Exercise 1

How might you expand your program to play rock/paper/scissors/lizard/spock? To learn more about this extension check the website:


  1. How do you test a tie in your program?

  2. How does the Table change, if paper=2, rock=0, and scissors=1? Redraw your table.

  3. To play with a different player, what do you need to change in your program? Remember you are using unicast to send your hand shape.

  4. What happens if you send your hand shape to the other player before they pick theirs? Will there be a problem? Could they cheat!?