Do I need to buy hardware for this tutorial?

No. Everything runs in the browser: Circuitly simulates the board, the components and the code. Real hardware is optional if you want to rebuild the circuit afterwards.

Which components are used?

Arduino UNO board, 5 mm LED, 220 Ω resistor. They are already available in the simulator library.

How long does it take?

About 10 minutes, beginner level, in 3 guided steps.

What should I know before starting?

The previous tutorial in the series, “Blink an LED”, is enough preparation. No software install is required.

Is the code provided and checked?

The simulator checks your wiring and your code automatically at every step, and shows the commented solution if you get stuck.

All tutorials

1 · First steps

Two alternating LEDs

Beginner10 min

Goal

Alternate two LEDs (pins 12 and 13) like a level crossing.

Why it matters

You learn to drive several independent outputs inside the same loop.

What you need

Arduino UNO board
5 mm LED
220 Ω resistor

Nothing to buy: every component below is simulated in the browser.

Steps

01Add a second LED + resistor on pin 12.
02Declare both pins as OUTPUT.
03In loop(), set one HIGH while the other is LOW, then swap.

This tutorial runs inside the Circuitly simulator: your wiring and your code are checked automatically at every step.

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Frequently asked questions

Do I need to buy hardware for this tutorial?: No. Everything runs in the browser: Circuitly simulates the board, the components and the code. Real hardware is optional if you want to rebuild the circuit afterwards.
Which components are used?: Arduino UNO board, 5 mm LED, 220 Ω resistor. They are already available in the simulator library.
How long does it take?: About 10 minutes, beginner level, in 3 guided steps.
What should I know before starting?: The previous tutorial in the series, “Blink an LED”, is enough preparation. No software install is required.
Is the code provided and checked?: The simulator checks your wiring and your code automatically at every step, and shows the commented solution if you get stuck.

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