⚡ Timer1 Input Capture Mode — Register-Level (Arduino UNO)

This project demonstrates Timer1 Input Capture Mode on ATmega328P (Arduino UNO) using register-level programming. The timer captures the value of TCNT1 whenever a rising edge appears on the ICP1 pin (PD6 / Arduino D8) and stores it in the ICR1 register. The captured timer value is displayed via Serial Monitor.

⚙️ Hardware Used

Arduino UNO (ATmega328P)

Signal Source → D8 (ICP1 pin)

USB connection for serial data output

🔌 Pin Configuration Function Arduino Pin ATmega328P Pin Port Input Capture (ICP1) D8 14 PD6 TX (Serial Out) D1 3 PD1 GND — — — 🧩 Registers Used Register Purpose TCCR1A / TCCR1B Configure Timer1 mode, edge select, and prescaler TIMSK1 Enable Input Capture Interrupt ICR1 Stores the captured timer value SREG Enables global interrupt TCNT1 Timer counter register TIFR1 Input Capture Flag (handled automatically on ISR) ⚙️ Timer Configuration

Mode: Normal Mode (WGM13:0 = 0)

Edge Select: Rising edge (ICES1 = 1)

Prescaler: 1024 (CS12 + CS10)

Interrupt: Input Capture Interrupt (ICIE1 = 1)

🧠 Working Principle

Timer1 counts continuously with a prescaler of 1024.

When a rising edge appears on the ICP1 (D8) pin:

The current timer value (TCNT1) is copied into ICR1.

The ISR (TIMER1_CAPT_vect) executes.

Inside the ISR, the captured value is printed via the Serial Monitor.

Each edge trigger gives a precise time measurement in timer ticks.

📏 Timing Calculation

At 16 MHz system clock with prescaler = 1024:

Timer frequency = 16,000,000 / 1024 = 15625 Hz Timer tick = 1 / 15625 = 64 µs per count

If ICR1 = 5000, → Captured time = 5000 × 64 µs = 0.32 seconds (320 ms) between two edges.

🧪 Example Output (Serial Monitor) Captured Value: 5000 Captured Value: 5200 Captured Value: 5100

Each value corresponds to the timer count at the moment the rising edge occurred.

💡 Applications

Frequency measurement

Pulse width and duty cycle analysis

Signal timing or RPM measurement

Ultrasonic or sensor timing experiments