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🔘 Push Button Interface — Register-Level (Arduino UNO)

This project demonstrates how to interface a push button switch with the Arduino UNO (ATmega328P) using register-level programming, without any Arduino functions.

⚙️ Hardware Used

  • Arduino UNO (ATmega328P)
  • Push Button Switch
  • LED (for output indication)
  • 220Ω Resistor (LED current limit)
  • Optional: Pull-down resistor (if not using internal pull-up)

🔌 Pin Configuration

Component Function Arduino Pin Port
Push Button Input D2 PD2
LED Output D12 PB4
VCC Power +5V —
GND Ground GND —

🧩 Code Explanation

  • DDRB |= (1 << DDB4) → Configures PB4 as output (LED).
  • DDRD &= ~(1 << DDD2) → Configures PD2 as input (button).
  • PORTD |= (1 << PD2) → Activates internal pull-up resistor.
  • Logic check:
    • Pressed (LOW) → LED ON
    • Released (HIGH) → LED OFF

⚙️ Working Principle

  1. When the button is pressed, PD2 goes LOW, LED turns ON.
  2. When released, PD2 goes HIGH (via pull-up), LED turns OFF.

🧰 Build & Upload

  1. Compile using AVR-GCC, Atmel Studio, or PlatformIO.
  2. Upload the HEX file to Arduino UNO.
  3. Watch the LED respond instantly to button presses.