For people new to using the Arduino IDE with various hardware, it might be worth pointing out that while a pullup is needed, and the Atmega328 has internal pullups when configured with INPUT_PULLUP, ...

If you want a button or switch as an input on a microcontroller (MCU), you can use a “pullup resistor” so that the input is seen as a logical high when the (normally open) switch or button is closed.

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Leonardo Russo’s ArduinoSimulator is an open-source Arduino Simulator written in JavaScript that runs code directly in your web browser and shows the serial output and digital/analog pins status for ...