Microbit Programming: Simple AI for Game Playing

Last week, we wrote our first game on Microbit: Catching Apples. My two sons loved playing it, competing for the highest score, which seems to be capped at 35 points.

The code for the Catching Apples game and the Microbit simulator: https://makecode.microbit.org/_DV93uT7i0WuK

Is there a limit? Even if we react quickly enough and make no mistakes, is there a scenario where we cannot catch the apple?

Introduction to AI – Letting the Computer Play

AI, known as artificial intelligence, is typically referred to as computers having human-like intelligence. We can teach Microbit how to play this game using a very simple strategy: move towards the apple (if the apple is above the plate, stay still). Let’s define a function called letComputerPlay.

function letComputerPlay() {
    if (pixel.x() < apple.x()) {
        moveRight();
    } else if (pixel.x() > apple.x()) {
        moveLeft();
    }
}

Then, we can place this function into the main game loop function. We can remove the code that handles the buttons (A and B keys) and provide corresponding functions to move left or right:

function moveLeft() {
    px--;
    if (px < 0) px = 4;
    pixel.setX(px);
}
 
function moveRight() {
    px++;
    if (px > 4) px = 0;
    pixel.setX(px);
}

The code and Microbit simulator: https://makecode.microbit.org/_93CihTgAFLk2

Success! Microbit knows how to play the game and will never get tired. In fact, Microbit is very good at playing this game.

Improved Version of MICROBIT AI – Game Strategy

If you let Microbit play for a while, you won’t see the game end because, theoretically, Microbit can always catch the apple, even if it starts the farthest away—it needs four moves to reach it, and the apple takes five moves to trigger the game over!

However, we can still optimize by choosing the shorter move direction. We just need to calculate the cost (steps) of moving left or right. This strategy will make Microbit appear smarter. Here is our improved version of MicrobitAI:

function letComputerPlay() {
    if (pixel.x() == apple.x()) {
        return ;
    }
    let costOfMovingLeft, costOfMovingRight;
    // Calculate the cost of moving left
    if (pixel.x() < apple.x()) { // Apple is on the right
        costOfMovingLeft = pixel.x() + 5 - apple.x();
    } else { // Apple is on the left
        costOfMovingLeft = pixel.x() - apple.x();
    }
    // Calculate the cost of moving right
    if (pixel.x() < apple.x()) { // Apple is on the right
        costOfMovingRight = apple.x() - pixel.x();
    } else { // Apple is on the left
        costOfMovingRight = 5 - pixel.x() + apple.x();
    }
    if (costOfMovingLeft < costOfMovingRight) { // Moving left is cheaper
        moveLeft();
    } else if (costOfMovingLeft > costOfMovingRight) {// Moving to the right is faster
        moveRight();
    } else if (Math.randomRange(0, 1) == 0) { // Random direction is fine
        moveLeft();
    } else {
        moveRight();
    }
}

As you can see, we first calculate the costs of moving left (costOfMovingLeft) and right (costOfMovingRight), and choose the shorter (better) direction as our strategy. In case both left and right costs are the same, we randomly choose a direction (using Math.randomRange(0, 1) to generate a number that is either 0 or 1, each with a 50% chance).

The code and Microbit simulator: https://makecode.microbit.org/_FpoaisRKC6ws

As you can see, the AI here is very simple – Microbit strictly follows human instructions to play the game. Microbit’s intelligence comes from decision making. It is very suitable for computers. The computation will make decisions based on the current situation, which can often be calculated based on existing conditions (variables).

Video: https://helloacm.com/wp-content/uploads/2019/12/microbit-plays-game-with-ai.mp4

Computers do not make mistakes and do not get tired – this is superior to humans.

English: https://helloacm.com/microbit-programming-introduction-to-ai-letting-computer-play-the-game/

Sync to blog: https://justyy.com/archives/31436

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Introduction to AI – Letting the Computer Play

Improved Version of MICROBIT AI – Game Strategy

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