You can already show messages and numbers on the micro:bit and respond to a button.

Today you will build a Reaction Timer: a short countdown, a random wait, a full-screen signal, and a reading in milliseconds when you press A. You will then run fair attempts and compare times as a class.

Before anyone runs the finished idea: when do you think the full screen should appear, and what should the number on the screen mean?

First, go to the Micro:bit website. Click on 'New Project' and name your project as 'Reaction Timer'.

Let's start by creating a welcome message that will be displayed when you power on your Microbit.

Add the following code to your project:

basic.showString("Get Ready")

After the welcome message, we are going to create a countdown from 3 to 1 and then show a line on the screen.

Add the following new code to your project:

basic.showString("Get Ready")
basic.showNumber(3)
basic.pause(1000)
basic.showNumber(2)
basic.pause(1000)
basic.showNumber(1)
basic.pause(1000)
basic.showLeds(`
    . . . . .
    . . . . .
    # # # # #
    . . . . .
    . . . . .
    `)

To make the game unpredictable, let's add a random delay after the countdown. 

Add the following new code to create a random delay between 1 to 5 seconds (1,000 to 5,000 milliseconds) and then show the signal (a fully lit up LED screen) to the player.

basic.showString("Get Ready")
basic.showNumber(3)
basic.pause(1000)
basic.showNumber(2)
basic.pause(1000)
basic.showNumber(1)
basic.pause(1000)
basic.showLeds(`
    . . . . .
    . . . . .
    # # # # #
    . . . . .
    . . . . .
    `)
basic.pause(Math.randomRange(1000, 5000))
basic.showLeds(`
    # # # # #
    # # # # #
    # # # # #
    # # # # #
    # # # # #
    `)