Same circuit, new board

An Arduino Uno names its pins by number, and the code must use the number of the pin the wire goes to. pinMode sets a pin as an output; digitalWrite switches it HIGH or LOW. The circuit ideas from the micro:bit carry straight over.

Most electronics kits, sensors and project guides assume an Arduino. The circuits are the ones you already know. What changes is the board, and then the language.

This is an Arduino Uno. Like the micro:bit it has pins, but they are named by number (0 to 13, plus A0 to A5), and it is programmed in C++. The board on this page runs the sketches for you; in Tinkercad Circuits you can build the same thing with blocks and see the C++ beside them.

void setup() {
  pinMode(13, OUTPUT);     // pin 13 is an output
}

void loop() {
  digitalWrite(13, HIGH);  // pin 13 on (5 V)
  delay(500);              // wait half a second
  digitalWrite(13, LOW);   // pin 13 off (0 V)
  delay(500);
}

Predict: Read the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.
Try: Try it on the board and compare the result with your prediction.
Investigate: Work out why it happens, one step at a time.
Modify: Change the problem on purpose and see what happens.
Practise: A few on your own, to check you have it.
Make: Make your own problem using what you have learned. Expect a few tries; that is normal.

WidthMore contexts, same idea.

PredictRead the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.

Which pin?

The LED (with its resistor) is wired to pin 12. The sketch above uses pin 13. When it runs, the LED…Blinks, but dimlyStays onBlinks: the code makes it blinkStays dark

TryTry it on the board and compare the result with your prediction.

Try: run it

Try it yourselfYour edits are saved in this browser.

Upload and run the sketch. What does the LED on pin 12 do?

Use the board. This ticks when you get there.

InvestigateWork out why it happens, one step at a time.

Worked example: read the pins

Worked exampleBefore each step, say what you think comes next.

$\text{pinMode(13, OUTPUT)}$ Sets pin 13 up as an output. Pin 13, not the LED's pin 12.
$\text{digitalWrite(13, HIGH)}$ Switches pin 13 to 5 V. Nothing is wired there.
$\text{digitalWrite(13, LOW)}$ Switches pin 13 back to 0 V.
$\text{LED on pin 12}$ Pin 12 is never set up or switched, so the LED stays dark.
$\text{fix: 12 in every line}$ Or move the wire to pin 13. Code and wiring must agree.

Now find every line to change.

Which lines must change so the sketch blinks the LED on pin 12?Only pinModeAll three: pinMode and both digitalWrite linesOnly the first digitalWriteNone: change the wire instead

Sam's LED is on pin 13. It doesn't blink: it just glows very dimly now and then. Click the line where Sam's sketch goes wrong.

ModifyChange the problem on purpose and see what happens.

Vary: change the pin

Try it yourselfYour edits are saved in this browser.

Need a hint?

Three lines name a pin.

Another hint

pinMode(12, OUTPUT); digitalWrite(12, HIGH); digitalWrite(12, LOW);

Change the sketch so the LED on pin 12 blinks. Upload and run it.

Use the board. This ticks when you get there.

Modify TypicalChange the problem on purpose and see what happens.

Build it in Tinkercad

In Tinkercad: an Arduino Uno, a 220 Ω resistor and an LED on pin 12 to GND. In Code › Blocks, blink pin 12. Then switch to Blocks + Text. I found pinMode and digitalWrite in the C++ beside my blocks.

PractiseA few on your own, to check you have it.

Pins

A buzzer is wired to pin 8. Which line sets it up?pinMode(8);digitalWrite(8, OUTPUT);pinMode(8, OUTPUT);pinMode(OUTPUT, 8);

An LED glows very dimly instead of lighting, and the pin numbers all match. What is the most likely cause?The pin was never set with pinMode(pin, OUTPUT)delay is too shortThe LED is the wrong way roundThe resistor is too small

MakeMake your own problem using what you have learned. Expect a few tries; that is normal.

Your own sketch

Try it yourselfYour edits are saved in this browser.

Need a hint?

setup() runs first: set the pin up there.

Another hint

pinMode(7, OUTPUT); in setup(), digitalWrite(7, HIGH); in loop().

Another hint

Every line ends with ;

The LED is wired to pin 7. Write the sketch to switch it on (and keep it on).

Use the board. This ticks when you get there.

For teachers

Students run a blink sketch whose pin number doesn't match the wiring, fix every pin number, see the dim pull-up glow of a missing pinMode, build the circuit on an Uno in Tinkercad blocks and read the C++ beside them, then write a short sketch for a new pin. About 40 minutes.

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

Students will be able to

I can match the pin numbers in a sketch to the wiring.
I can set a pin as an output and switch it on and off.
I can find the C++ behind Tinkercad's blocks.

Before class

The board in the lesson runs a subset of Arduino C++ against a model of an Uno (5 V pins, an LED and resistor per pin, simulated time). It behaves like the real board for the things these lessons teach: a missing ; stops the upload, a pin written HIGH without pinMode glows dimly (the internal pull-up), = in an if assigns. It is not a full compiler; real hardware comes in the next unit.

Tinkercad: Arduino Uno R3 is in the components list; Code › Blocks + Text shows the generated C++ beside the blocks (it can't be edited until you switch to Text). Same class code as the micro:bit unit.

Running the lesson

Predict: ask students to point at the pin number in each line of the sketch.
Find the mistake: the dim glow is a real effect students will see on hardware; name it the pull-up.
Tinkercad: ask which block made which line of C++.

The hard part (on purpose)

C++ looks dense after blocks. Read it aloud line by line and point at the pin number in each.

When students get stuck

A student changes only pinMode. Ask: Which pin does each digitalWrite line switch? Fix: Every line that names a pin.
Upload fails with a ; error. Ask: Which line does the message name, and how does it end? Fix: Every statement ends with ;

Stretch and support

Stretch: Wire a second LED on pin 9 and blink them in turn.

Support: A printed sketch with the pin numbers highlighted.

Where it leads

Next: Reading the C++ (what setup() and loop() do, and timing with delay).

Circuits with the micro:bit: the same loop and resistor ideas.

Sources

Tinkercad Circuits (Autodesk): simulator, link only (checked 12 October 2026)
Arduino language reference (link) (checked 12 October 2026)
SparkFun Inventor's Kit Experiment Guide v4.1 (benchmark; CC BY-SA 4.0) (checked 12 October 2026)

What each step is for

which pin?: Committing to what happens when the code names a different pin from the wire tests the new move: pin numbers in code must match the wiring. The wrong options are the 'code works whatever pin' picture.
Try: run it: Running the sketch settles the prediction: the board shows pin 13 not wired, and the LED on pin 12 never changes.
Worked example: read the pins: Reading each line for its pin number models the move: every pin number must be the wired pin. Sam's half-changed sketch is planted after the method, with its real symptom (a dim glow from the pull-up).
Vary: change the pin: Changing every pin number in the code, then running it, applies the move directly.
Build it in Tinkercad: Building the circuit on an Uno in Tinkercad with blocks, then opening the Blocks + Text view, shows that the blocks are this C++.
pins: Reading pin numbers and modes in short sketches, with the pull-up glow as the symptom of a missing pinMode.
your own sketch: Writing pinMode and digitalWrite from scratch for a new pin puts the lesson's two lines together without a model to copy.

Now you can

Match the pin numbers in a sketch to the wiring.
Set a pin as an output and switch it on and off.
Find the C++ behind Tinkercad's blocks.

Next lesson2. Reading the C++Every sketch has two parts: setup() runs once when the board starts, then loop() runs again and again for ever. delay(ms) waits that many milliseconds, so the delays set the timing of a blink.

Source: content/engineering/arduino/pins/lesson.md