INPUT_PULLUP
Keeps the input HIGH until the switch connects it to GND.
Arduino sample guide
roboda-sample-0252 - Digital Input Pullup 11
Read a button or limit switch reliably using the internal pullup resistor.
Step-by-step build
Read buttons, limit switches, and contact sensors with stable internal pullups.
1
Wire one side of the switch to the input pin and the other side to GND.
2
Enable INPUT_PULLUP so no external resistor is required.
3
Treat LOW as pressed and HIGH as released.
4
Mirror the state to D13 and Serial Monitor.
Important code parts
These are the sections learners should understand before changing the sketch.
bool pressed
Converts the raw pin read into a meaningful state.
Serial.println()
Prints the state so learners can debug wiring.
Pin mapping for this sample
Use this first table for the exact sample wiring, then use the board-family table when moving the sketch to another Arduino board.
| Code name | Sample pin | Mode | Connect to | Note |
|---|---|---|---|---|
| buttonPin | D12 | INPUT_PULLUP | Push button or limit switch to GND | Pressed reads LOW because the internal pullup is enabled. |
| outputPin | D13 | OUTPUT | Built-in LED or indicator LED through resistor | D13 is safe for the onboard LED on most Arduino boards. |
Arduino board pin reference
The code names stay the same; only the physical board pins may change by family. Always confirm with the board silkscreen when using clones or special variants.
| Board family | Digital | PWM | Analog | I2C | SPI | Interrupt |
|---|---|---|---|---|---|---|
| Uno / Nano / Pro MiniDefault target for these samples. | D0-D13 | D3, D5, D6, D9, D10, D11 | A0-A5 | A4 SDA, A5 SCL | D10 SS, D11 MOSI, D12 MISO, D13 SCK / ICSP | D2, D3 |
| Mega 2560Best for many sensors or multiple serial ports. | D0-D53 | D2-D13, D44-D46 | A0-A15 | D20 SDA, D21 SCL | D50 MISO, D51 MOSI, D52 SCK, D53 SS / ICSP | D2, D3, D18, D19, D20, D21 |
| Leonardo / MicroUSB serial can behave differently because the main MCU handles USB. | D0-D13 | D3, D5, D6, D9, D10, D11, D13 | A0-A5 plus extra analog-capable pins by board | D2 SDA, D3 SCL | ICSP header | D0, D1, D2, D3, D7 |
| Nano Every / Uno WiFi Rev2Check the board package pinout for exact PWM labels. | D0-D13 | PWM-marked digital pins | A0-A7 on Nano Every, A0-A5 on Uno WiFi Rev2 | SDA/SCL marked pins | ICSP/SPI marked pins | Use pins supported by digitalPinToInterrupt() |
| Uno R4 Minima / Uno R4 WiFi5V logic board; still confirm shield/library compatibility. | D0-D13 | PWM-marked digital pins | A0-A5 | SDA/SCL marked pins | ICSP/SPI marked pins | Use digitalPinToInterrupt(pin) |
| Due3.3V logic only; protect pins from 5V sensors. | D0-D53 | PWM-marked digital pins | A0-A11 | SDA/SCL and SDA1/SCL1 | SPI header | Use digitalPinToInterrupt(pin) |
| MKR / Nano 33 family3.3V logic. Some AVR-only libraries may need alternatives. | Board-marked digital pins | PWM-marked pins | Board-marked analog pins | SDA/SCL marked pins | SPI marked pins | Use digitalPinToInterrupt(pin) |
Full sample code
/*
Roboda verified Arduino sample 0252
Feature: Digital Input Pullup
Generated for online build, classroom practice, and hardware upload testing.
*/
const byte buttonPin = 12;
const byte outputPin = 13;
void setup() {
pinMode(buttonPin, INPUT_PULLUP);
pinMode(outputPin, OUTPUT);
Serial.begin(9600);
}
void loop() {
bool pressed = digitalRead(buttonPin) == LOW;
digitalWrite(outputPin, pressed ? HIGH : LOW);
Serial.println(pressed ? "pressed" : "released");
delay(430);
}
Teacher notes
- Compile the sample before changing wiring or constants.
- When changing boards, keep the code names the same and update only the pin number constants.
- For 3.3V boards, level-shift 5V sensors and modules before connecting signal pins.
- Use the first compiler error and the Roboda diagnostic suggestion before fixing later warnings.