Push button input : pull-up logic

Push button input : pull-up logic

Main Diagram
Last revision • 25/06/2025

Hardware Required

  • PICUNO Microcontroller board
  • 1 × LED
  • 1 × 220Ω resistor
  • 1 × Push Button (4-pin or 2-pin)
  • 1 × 10kΩ resistor
  • Breadboard
  • Jumper wires
  • USB cable

Description

This project demonstrates pull-up logic. When the button is pressed, the pin reads LOW and the LED turns ON.

Circuit Diagram

[Fritzing image to be added here]

Circuit

  • Connect the PICUNO board to the computer using a USB cable.
  • Connect the anode (longer leg) of the LED to GPIO 2 through a 220Ω resistor.
  • Connect the cathode (short leg) of the LED to GND.
  • Connect one leg of the push button to GND.
  • Connect the other leg of the button to GPIO 3.
  • Connect one end of the 10kΩ resistor to GPIO 3 and other end to 3.3V.

Schematic

Button one side → GND

Other side → GPIO 3

GPIO 3 → 10kΩ → 3.3V

GPIO 2 → 220Ω → LED anode

LED cathode → GND

Code - C

#define LED_PIN 2
#define BUTTON_PIN 3

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT);
}

void loop() {
  if (digitalRead(BUTTON_PIN) == LOW) {
    digitalWrite(LED_PIN, HIGH);
  } else {
    digitalWrite(LED_PIN, LOW);
  }
  delay(10);
}
digitalRead(BUTTON_PIN) == LOW - Detects button press.

digitalWrite(LED_PIN, HIGH/LOW) - Controls LED based on button state.

Code - Micropython

from machine import Pin
import time

led = Pin(2, Pin.OUT)
button = Pin(3, Pin.IN)

while True:
    if button.value() == 0:
        led.value(1)
    else:
        led.value(0)
    time.sleep(0.01)
button.value() == 0 - Detects when button is pressed (LOW).

led.value(1) / value(0) - Turns LED ON or OFF.