Examples

Use the built-in pull-up

Reads a button with INPUT_PULLUP and no external resistor — pressed reads 0.

Arduino Uno R30 libraries46 linesOverall confidence 100%

SourceRead onlydigital_input_pullup.ino

/* Input Pull-up Serial This example demonstrates the use of pinMode(INPUT_PULLUP). It reads a digital input on pin 2 and prints the results to the Serial Monitor. The circuit: - momentary switch attached from pin 2 to ground - built-in LED on pin 13 Unlike pinMode(INPUT), there is no pull-down resistor necessary. An internal 20K-ohm resistor is pulled to 5V. This configuration causes the input to read HIGH when the switch is open, and LOW when it is closed. created 14 Mar 2012 by Scott Fitzgerald This example code is in the public domain. https://docs.arduino.cc/built-in-examples/digital/InputPullupSerial/ */ void setup() { //start serial connection Serial.begin(9600); //configure pin 2 as an input and enable the internal pull-up resistor pinMode(2, INPUT_PULLUP); pinMode(13, OUTPUT); } void loop() { //read the pushbutton value into a variable int sensorVal = digitalRead(2); //print out the value of the pushbutton Serial.println(sensorVal); // Keep in mind the pull-up means the pushbutton's logic is inverted. It goes // HIGH when it's open, and LOW when it's pressed. Turn on pin 13 when the // button's pressed, and off when it's not: if (sensorVal == HIGH) { digitalWrite(13, LOW); } else { digitalWrite(13, HIGH); } }

What the parser saw

Extracted from #include · #define · pinMode · constructor arguments. The output of a deterministic parser, not an AI.

Parts

buttonusage pinMode(2, INPUT_PULLUP)

50%

ledusage pinMode(13, OUTPUT)

50%

Buses

—

Libraries

No libraries — read from pin names and pinMode alone.

Pin contract

An immutable contract owned by the project. It survives level changes; on a target board only the physical pins are remapped.

Logical name	Pin	Direction	Signal	Declared as
2	D2	in	digital	literal
13	D13	out	digital	literal

This page passes no verification gate. Logic (simulator), electrical (ERC · DRC) and physical (your confirmation) verification each run separately inside a project.

Next step

Same sketch, from simulation to PCB

The code stays as it is. Run it on avr8js in the Playground; import it into a project and the 8-pass electrical verification, KiCad board generation and Gerber export follow.

Run in Playground Import into a project