Workshop Wednesday – micro:bit – Show Message


Step One

To get started please visit and select the Let’s Code link from the website navigation bar.


Step Two

Once on the Let’s Code page look for the JavaScript Blocks Editor (PXT) section and select the Let’s Code button.


Step Three

Then that will take you to the JavaScript Blocks Editor (PXT), you then should select the JavaScript tab.


Step Four

Once you have the JavaScript tab selected, you should enter the following code:

const items: string[] = [
    "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
    "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z",
    "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "!", "?", " "

const means a value that doesn’t change and this is set to a string[] called items which is a special kind of value known as an array, which is a list of values, these can be identified with the use of a set of two square brackets, here it is a list of string. To get a particular value from an array you need an index, which is the position in the array, this starts from 0 for the first item and 1 for second and so on, so for example to get the fifth value from the array you’d use the index of 4.

Step Five

While still in the JavaScript tab, below the code entered in the previous step, you should enter the following code:

let counter: number = 0;
let editing: boolean = false;
let display: string = "";
let message: string = "";

let helps create another kind of value, these can change and are know as variables which can contain a single value, there are different types of value used here. First there’s a number which can store a whole number such as 0, 1, 2, 3 and so on. Then there’s a boolean this can be either true or false and here is set to false. Then there are two strings and this can be any kind of text, they have been set to an empty string which is “”

Step Six

Again while still in the JavaScript tab, below the code entered in the previous step, you should enter the following code:

function show(item: string) {

function is a block of code that you can use many times to do the same thing, they can also take in values known as parameters to use in the function. The parameter used here is called item and it is a string. The function will use this value to use or call the basic.showString built in function to display text on the micro:bit using the LEDs on the front.

Step Seven

Once again while still in the JavaScript tab, below the code entered in the previous step, you should enter the following code:

input.onButtonPressed(Button.A, () => {
    if (counter == items.length) {
        counter = 0;
    display = items[counter];

input.onButtonPressed(Button.B, () => {
    message += display;

input.onButtonPressed(Button.AB, () => {
    editing = !editing;

input are things that happen, also known as events, when you do something with the micro:bit, they are as follows:

  1. The first input is when you press the A button on the micro:bit and when you do it will check the counter to see if it is the same value as the size or length of the list string[] array, then it will set display to be the item from the array with the same index as the counter – if this is the first item it will have the value “A”, if second it will be “B” and so on, the line counter++ will increase the value of counter by one for the next item.
  2. The second input is when you press the B button on the micro:bit and when you do the message += display will add the whatever is in the display value onto the end of the message value, it will display a “+” on the micro:bit by using the function show briefly before continuing.
  3. The third input is when you press both the A and B buttons on the micro:bit at the same time editing = !editing; will set the value of editing to the opposite of its value, this is what the ! does which is known as “not”.

Step Eight

Finally while still in the JavaScript tab, below the code entered in the previous step, you should enter the following code:

basic.forever(() => {
    if (editing) {
    else {

basic.forever is a function which will repeat, or loop, forever as long as the example is running on the micro:bit. Inside this function it will check the editing value in an if statement, when it is true the first part of the code will happen, this will show the display value on the micro:bit and in the second part, when editing is false it will show the message value on the micro:bit instead.

Step Nine

That completes the example, in the JavaScript tab of the JavaScript Blocks Editor (PXT) there should be the following code:


Step Ten

Once the example is complete is should have started automatically, if not you can select the Play button near the “on-screen” micro:bit to start the example


Step Eleven

You can create a message by pressing the A+B button on the “on-screen” micro:bit then press the A button to cycle through the list of letters and numbers and then press B button to add the letter or number to the list to be displayed, you can keep doing this to add more letters and numbers then once the message is complete press A+B again to display the full message.


You can also run the example on an actual micro:bit by connecting one to your computer and then choosing the Download option in the JavaScript Blocks Editor (PXT) to download the example to your computer. Once downloaded you can then copy the .hex file from where you’ve downloaded it to the micro:bit the same was you’d copy to another drive or device connected to your computer. Then once the example has been copied to the micro:bit it should start automatically.


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