Send data to the computer

A micro:bit sends each sensor reading down the USB cable as a line of text, such as light:128. The computer turns the stream of lines into a graph.

Weather stations, heart-rate monitors and the sensors in a science lab all do the same simple thing: send a reading, wait, send the next. A computer collects the readings and draws the graph.

In micro:bit Foundations, everything you made stayed on the micro:bit. Now it talks to the computer it is plugged into. A cable that sends text one line at a time is called serial.

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.

WidthMore contexts, same idea.

Explain it to me

Serial sends text down the USB cable, one line at a time.

serial write value sends a named reading, such as light:128.
Put it in forever with a pause to send a reading again and again.
The computer turns the lines into a table or a graph.

Show as code

basic.forever(function () {
    serial.writeValue("light", input.lightLevel())
    basic.pause(500)
})

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

send.ts

basic.forever(function () {
    serial.writeValue("light", input.lightLevel())
    basic.pause(500)
})

This program runs on a micro:bit plugged into a computer. What arrives at the computer every half second?A picture of the LEDsJust the number 128A line of text, such as light:128A graph

RunRun it and compare the result with your prediction.

Run

Run it in the simulator. Under the micro:bit, click Show data (it appears once a program sends values) to see the readings as numbers and as a graph. Drag the simulator's light level up and down.

Show as code

send.ts

basic.forever(function () {
    serial.writeValue("light", input.lightLevel())
    basic.pause(500)
})

Try it yourselfYour edits are saved in this browser.

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

I changed the light level in the simulator and watched the values change under Show data.

Run TypicalRun it and compare the result with your prediction.

On a real micro:bit

Click Download in the editor and copy the program to your micro:bit. Leave it plugged in, then click Connect a micro:bit below and choose it. Cover the micro:bit with your hand, then shine a torch on it.

Try it yourselfYour edits are saved in this browser.

Download the program to a micro:bit, connect it, and collect at least 10 light readings.

Use the board. This ticks when you get there.

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

Investigate

Show as code

send.ts

basic.forever(function () {
    serial.writeValue("light", input.lightLevel())
    basic.pause(500)
})

Ben's program:

Show as code

serial.writeValue("light", input.lightLevel())

Why does each line start with a name (light:)?To make the number biggerSo the micro:bit remembers itThe cable needs a name to workSo the computer can tell different values apart when there are several

You delete the pause. What happens?One reading is sent, then it stopsNothing is sentThe readings get more accurateReadings pour out as fast as the micro:bit can send them, far more than you need

Ben's program sends one reading when the micro:bit starts, then nothing. Why?Light level only works onceThe board can only read one lineThe cable is brokenThe block is in on start, not in forever, so it runs only once

ModifyChange the code on purpose and check the result.

Modify

Send the temperature too, with its own name. In Show data (or on the board), each name gets its own line.

Need a hint?

Add a second serial write value inside forever, named temperature, with temperature (°C) from Input.

Make it send ten readings a second.

Need a hint?

Change the pause so it sends ten readings a second.

Try it yourselfYour edits are saved in this browser.

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

Send the temperature as well as the light level, each with its own name.

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

Send ten light readings a second.

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

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

Make

Make a tilt logger: send the micro:bit's x and y acceleration five times a second, and send the line mark when A is pressed, so you can mark a moment on the record. Tilt it in the simulator and watch Show data.

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?

Acceleration (mg) is in Input; choose x, then y.

Another hint

Two serial write value blocks in forever: x and y. On button A pressed: serial write line mark.

A tilt logger: send x and y acceleration five times a second, and send the line mark when A is pressed.

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

For teachers

Students make a micro:bit send sensor readings to the computer over USB as named lines of text, and watch them graphed. About 45 minutes.

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

Students will be able to

I can send a sensor reading to the computer again and again.
I can explain what travels down the cable (a named line of text).
I can send two values and choose how often they are sent.

Before class

The idea: a micro:bit plugged into a computer can send text down the USB cable, one line at a time (this is called serial). serial write value sends a line such as light:128: a name, a colon and a number. Whatever is on the other end (MakeCode's Show data, the board in this lesson, a spreadsheet) turns those lines into a table or a graph.

Without micro:bits: the MakeCode simulator shows the values under Show data, so every required step works in the browser. The board step ("On a real micro:bit") is optional and needs a micro:bit, a data USB cable and Chrome or Edge.

With micro:bits: students download the program, leave the micro:bit plugged in, and click Connect a micro:bit on the board. Only one page can use the cable at a time, so if MakeCode is connected to the micro:bit, disconnect it there first.

Running the lesson

Predict: most say a graph. Ask: who draws the graph, the micro:bit or the computer?
Run: Show data appears under the simulator once values arrive.
On a real micro:bit: covering it and shining a torch makes a clear graph.
Investigate: Ben's logger is the on start versus forever slip from Foundations.

The hard part (on purpose)

The text format links the micro:bit and the board. When nothing shows, ask whether the program is running and the write block is inside forever.

When students get stuck

Show data never appears. Ask: Is the program running? Is serial write value inside forever? Fix: Restart the simulator; put the send inside forever.
Connect a micro:bit lists nothing. Ask: Are you in Chrome or Edge, with a data cable? Fix: Use Chrome or Edge; try another cable (some only charge).
Only one reading arrives. Ask: Which block is the send in? Fix: Move it into forever with a pause.

Stretch and support

Stretch: Send the sound level too, and find out which is noisier: the classroom or the corridor.

Support: Give the Make program with x done; students add y and the button.

Where it leads

Next: the computer sends commands to the micro:bit. Real world: data loggers in science labs, weather stations and fitness trackers.

What each step is for

On a real micro:bit: The same lines arrive from a real micro:bit, and a different program (this board) can graph them: the text format is what connects the two.
Investigate: Each reading is a named line of text sent again and again; the name tells values apart and the pause sets how often a reading is sent.
Modify: A second named value appears as its own line on the graph; changing the pause changes how often readings arrive.

Now you can

Send a sensor reading to the computer again and again.
Explain what travels down the cable (a named line of text).
Send two values and choose how often they are sent.

Next lesson2. Commands from the computerThe computer can send lines of text too. The micro:bit reads each whole line and its program decides what the word means, so both sides must agree on every word.

Source: content/code/microbit-computer/send-data/lesson.md