Send and receive

Send a number by radio, and react on another micro:bit when it arrives.

Wireless doorbells, car keys and walkie-talkies all send small radio messages to a receiver tuned to the same channel.

Micro:bits can talk to each other by radio. One sends a message; every micro:bit nearby in the same group (like a walkie-talkie channel) receives it. You find radio blocks in Radio.

As soon as your program uses radio, the simulator shows two micro:bits. Both run the same program, so you can press a button on one and watch the other.

Predict: Read the code and say what it will do before you run anything. A wrong guess is fine: it shows you what to look for.
Run: Run it and compare the result with your prediction.
Investigate: Trace how each line of code connects to what you see.
Modify: Change the code on purpose and check the result.
Make: Build something new using what you have learned. Expect a few tries; that is normal.

Explain it to me

Radio sends messages between micro:bits · Sound on for the voiceover

radio set group picks a channel. Only micro:bits in the same group hear each other.

send number sends to every other micro:bit in the group (not to itself).

on radio received is an event: it runs each time a message arrives.

Show as code

radio.setGroup(1)
input.onButtonPressed(Button.A, function () {
    radio.sendNumber(1)
})
radio.onReceivedNumber(function (receivedNumber) {
    basic.showIcon(IconNames.Heart)
    basic.pause(500)
    basic.clearScreen()
})

The example, as blocks

What it makes

PredictRead the code and say what it will do before you run anything. A wrong guess is fine: it shows you what to look for.

Predict

Show as code

lesson.ts

radio.setGroup(1)
input.onButtonPressed(Button.A, function () {
    radio.sendNumber(1)
})
radio.onReceivedNumber(function (receivedNumber) {
    basic.showIcon(IconNames.Heart)
    basic.pause(500)
    basic.clearScreen()
})

send number sends; on radio received waits for a message to arrive.

There are two micro:bits running this program. You press A on the first one. What happens?The heart shows on the second micro:bitThe heart shows on bothThe heart shows on the first micro:bitNothing happens

RunRun it and compare the result with your prediction.

Run

Press A on the first micro:bit, then on the second.

Show as code

lesson.ts

radio.setGroup(1)
input.onButtonPressed(Button.A, function () {
    radio.sendNumber(1)
})
radio.onReceivedNumber(function (receivedNumber) {
    basic.showIcon(IconNames.Heart)
    basic.pause(500)
    basic.clearScreen()
})

Try it yourselfYour edits are saved in this browser.

It takes a few seconds to load. Your work in this step is kept.

I pressed A on each micro:bit in turn and watched which one showed the heart.

InvestigateTrace how each line of code connects to what you see.

Investigate

Show as code

lesson.ts

radio.setGroup(1)
input.onButtonPressed(Button.A, function () {
    radio.sendNumber(1)
})
radio.onReceivedNumber(function (receivedNumber) {
    basic.showIcon(IconNames.Heart)
    basic.pause(500)
    basic.clearScreen()
})

Match each radio block with its job.

Ella's two micro:bits are set to different groups.

radio.set_group(1)
def on_button_pressed_a():
    radio.send_number(1)
input.on_button_pressed(Button.A, on_button_pressed_a)
def on_received_number(receivedNumber):
    basic.show_icon(IconNames.HEART)
    basic.pause(500)
    basic.clear_screen()
radio.on_received_number(on_received_number)

Like a button, a radio message is an event: the micro:bit calls a function each time one arrives.

Match each block with what it does.

radio set group 1

radio send number 1

on radio received

Ella loads the program onto two real micro:bits. Pressing A on either does nothing. She changed one to radio set group 2. Why does nothing arrive?Radio only works in the simulatorsend number needs a pauseThe two micro:bits are in different groups, so neither hears the otherGroup 2 is broken

The same program in Python. Match each line with what it does.

radio.send_number(1)

def on_received_number(receivedNumber):

radio.on_received_number(on_received_number)

ModifyChange the code on purpose and check the result.

Modify

Make a shake send a message too. Shake one micro:bit and watch the other.

Need a hint?

Drag in on shake from Input.

Another hint

Put radio send number inside it.

In a classroom full of micro:bits, everyone on group 1 hears everyone else. Choose your own group number (0 to 255) and agree it with your partner.

Try it yourselfYour edits are saved in this browser.

It takes a few seconds to load. Your work in this step is kept.

Make a shake send a message too, so the heart also shows on the other micro:bit.

This ticks by itself when your blocks do what is asked.

I changed the group to a number of my own, so only my micro:bits hear each other.

InvestigateTrace how each line of code connects to what you see.

Mix it up

A function from last lesson, with no radio in it.

Show as code

lesson.ts

function flash () {
    basic.showIcon(IconNames.Heart)
    basic.pause(200)
    basic.clearScreen()
    basic.pause(200)
}
input.onButtonPressed(Button.A, function () {
    flash()
    flash()
})
input.onGesture(Gesture.Shake, function () {
    flash()
})

flash is called twice from A and once from shake. You press A, then shake. How many flashes in all?

MakeBuild something new using what you have learned. Expect a few tries; that is normal.

Make

Make a doorbell. Pressing A on the front door's micro:bit sends a number. The micro:bit inside calls a function, ring, that flashes a bell or a face (your choice).

Try it yourselfYour edits are saved in this browser.

It takes a few seconds to load. Your work in this step is kept.

Need a hint?

Make a function ring that flashes a picture, and call it from on radio received.

Another hint

On the sender: on button A pressed, radio send number 1.

A doorbell: A sends a number, and the other micro:bit calls a function of yours when it arrives.

This ticks by itself when your blocks do what is asked.

ModifyChange the code on purpose and check the result.

Change a quiet signal

A teacher presses A, and every student's micro:bit shows a raised hand: time to listen. Choose your own picture and group, then make B send the signal too.

Try it yourselfYour edits are saved in this browser.

It takes a few seconds to load. Your work in this step is kept.

For teachers

Students send a number by radio and react on another micro:bit when it arrives, and see that only micro:bits in the same group hear each other. About 40 minutes.

Open the teacher guide: answers, solutions, slides and a worksheet.

Students will be able to

I can send a number from one micro:bit to another.
I can react when a radio message arrives.
I can say why both micro:bits need the same group.

Before class

Radio sends short messages between micro:bits. radio set group chooses a channel (0 to 255); only micro:bits in the same group hear each other. send number sends to every other micro:bit in the group (never to itself). on radio received is an event: it runs each time a message arrives. In the simulator, a second micro:bit appears once the program uses radio; both run the same program. Using the number that arrived (receivedNumber) is next lesson. With real micro:bits in a classroom, pairs must choose their own group number or they will hear everyone.

Running the lesson

Predict: many students say 'on both'. Ask: who is listening, and who is talking? Or: does a walkie-talkie play your own voice back to you?
Run: press A on each micro:bit in turn. The heart always shows on the other one.
Investigate: Ella's groups are the most common real-classroom problem. The Python peek shows radio received as one more function the micro:bit calls.
Modify: any event can send. Then each pair picks a group.
Mix it up: counting function calls, from last lesson.
Make: the doorbell calls a function from on radio received.

The hard part (on purpose)

Two micro:bits, one group, and a micro:bit never hears itself. When nothing arrives, ask which one is sending and which group each is in.

When students get stuck

Nothing arrives. Ask: Are both micro:bits in the same group? Are you pressing on the sender? Fix: Check radio set group on both, and press on one while watching the other.
The heart shows on the micro:bit that was pressed. Ask: Is there a show icon inside the button event as well? Fix: Keep the button event for sending only; showing belongs in on radio received.
The second micro:bit is missing from the simulator. Ask: Is there a radio block in the program? Fix: The second micro:bit appears once any radio block is used.

Stretch and support

Stretch: Make the doorbell ring differently for a shake (a knock) and for A (the bell). How does the receiver know which? (Next lesson.)

Support: Give students the ring function already made, and ask them to add the sender and the receiver.

Where it leads

Next lesson: the number that arrives can say which message it was, so one receiver does different things. Class idea: a relay where a message passes around the room micro:bit to micro:bit.

What each step is for

Investigate: send number reaches every other micro:bit in the same group, and on radio received is an event that runs each time a message arrives.
Modify: Any event can send a message, and a group number of your own keeps your micro:bits to themselves.
Mix it up: A function runs once for each call, wherever the call is.

Now you can

Send a number from one micro:bit to another.
React when a radio message arrives.
Say why both micro:bits need the same group.

Next lesson3. Which message?Use the number that arrives by radio to do something different for each message, and send words as well as numbers.

Source: content/code/microbit-play/microbit-radio/lesson.md