FIT / MAKER LAB
Small sketches.
Real understanding.
Write a little, predict what happens, then explore the logic. Take your sketch to a real board when you’re ready.
Your sketch
Ready to editFollow the order of instructions and see how delay changes a signal.
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Change the first delay to 200 and the second to 800. Predict the HIGH and LOW durations, then preview again.
Logic preview
Virtual timePreview setup once, then a few loop passes. Step through the trace at your own pace.
The button setting applies to all INPUT_PULLUP reads for the entire preview.
Your trace will appear here.
Try the starter, then change one instruction.
Preview language & limits
Supported: decimal whole numbers, int and const int variables, assignment, + and −, comparisons, !, if / else with braces, setup() and loop(), pinMode, digitalWrite, digitalRead, delay, Serial.begin and Serial.println. Print a quoted string or a number; comments are allowed.
Modes: OUTPUT and INPUT_PULLUP. UNO pins: 0–13. ESP32 pins: 4, 13, 14, 18, 19, 21–23, 25–27, 32–33. LED_BUILTIN is available only for UNO.
Limits: 8 loop passes, 256 events, 60 seconds of virtual time, 10 seconds per delay and whole numbers within ±1,000,000. No integer-width overflow model. Source size and expression depth are also bounded.
Other C++ features, libraries, arrays, for / while loops, functions, analog I/O, PWM, interrupts, networking and peripherals are unsupported. This is not a compiler check; passing the preview does not prove a sketch will compile or work on hardware.
BEFORE YOU WIRE
Arduino UNO R3
ATmega328P • 5 V logic • 14 digital I/O pins • 6 analog inputs
Blink uses the built-in LED on D13. For the button lesson, connect a momentary switch between D2 and GND. INPUT_PULLUP means released is HIGH and pressed is LOW.
This profile is UNO R3, not UNO R4 or another Arduino board. External LEDs need a series resistor; never connect a motor directly to a GPIO pin.
| Pin | Use / restriction |
|---|---|
| D13 | Built-in LED / digital output |
| D2 | Button input in these lessons |
| D0 / D1 | Serial RX / TX; avoid extra wiring while using Serial |
| A0–A5 | Analog inputs; not modelled in this preview |
Take it to your board
- Export your sketch and open it in Arduino IDE.
- Select your exact board and its installed board package, then use Verify to compile.
- Check the official pinout and wiring before uploading. This preview has not tested your circuit.