POV — Persistence of Vision Display

• ATmega328P
• AVR
• Hardware interrupts (INT0)
• Timer1 CTC
• Hall-effect sensor
• Real-time timing

What it is

A persistence-of-vision display: a single column of 8 LEDs on a spinning arm, flashed at exactly the right instants so your eye fuses the flashes into stable text and patterns floating in the air. There's no screen — the image only exists because of precise timing synchronized to the rotation.

How it works

• Revolution sync. A Hall-effect sensor triggers an external interrupt (INT0) once per rotation, marking the exact start of each frame.
• Column clocking. Timer1 in CTC mode emits 120 evenly-spaced columns per revolution, and the LED byte for each column is written just in time.
• Auto-adaptive timing. The firmware re-measures the rotation period every revolution and rescales the column interval, so the image stays stable even as the motor's RPM drifts.

Why it's built this way

This project is pure real-time discipline: the whole illusion collapses if the timing is off by a little. Doing it bare-metal on an AVR — with a hardware interrupt for the position reference and a hardware timer for the columns — is the natural, jitter-resistant way to hit that requirement. The adaptive re-measurement is what makes it robust in the real world instead of only at one fixed speed.