🔘 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.

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⚙️ 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)

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🔌 Pin Configuration

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

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🧩 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

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⚙️ 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.

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🧰 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.