The Autophenakistoscope

By Dan Rasmussen
Category: Arduino, Electronics
Time Required: A weekend
Difficulty: Easy

Motorize a phenakistoscope, a 19th-century parlor novelty that preceded motion pictures, and keep its frames synched to an LED strobe by using a sensor and an Arduino microcontroller.

Invented in 1832 by Joseph Plateau, this device creates a moving picture from a sequence of stills arranged on a spinning disk and viewed through strategically cut slits. It’s easy to see how this invention and others like it evolved into movies and television.

My 9-year-old daughter and I wanted to make something new with Lego Mindstorms. We had a strobe, and we thought of combining it with a spinning disk to create animation. But it was difficult attaching the disk to the Lego motor, and we couldn’t control the motor and strobe speeds precisely enough to get them to match. The project really came together once we started using a gearmotor to give the disk a smooth, finely controllable rotation speed.

With an adjustable-frequency strobe, we experimented with persistence of vision and sympathetic frequencies, and produced several interesting visual effects. Finally, using an Arduino, a simple C program, and a sensor, we automatically synchronized the strobe with the rotating disk. A switch toggles between manual and microcontroller strobe control.

Steps

Step #1: Prepare the image disc and synchronization wheel.

Download and print a sample disk image and the templates in the documents area. Print the disk image in color, ideally on a laser printer so the colors won’t bleed if the disk gets wet.

Conclusion

Time and motion studies

Just like the movies, the Autophenakistoscope works best in low light. Dim the lights and plug it in. It first spins up the motor to half power, flashes the LED a few times, then starts reading inputs from the potentiometers. When the motor pot is turned all the way down, the motor should be off. When the strobe pot is all the way down, it should flash about once per second (1Hz).

Adjust the motor and the flash frequency to a moderate level. Toggle the mode switch once or twice to figure out which is which — in automatic mode, the image should stabilize; in manual mode, it will wander or not be legible.

It’s time to experiment. Adjust the knobs and you’ll see that multiple frequency combinations can produce smooth moving images. It’s also possible to freeze the image by adjusting the rotational frequency to match the strobe frequency.

When I first built this project, I noticed that the image can “roll” just like it used to on the old black-and-white TV when I was a kid. It turns out that this is a completely analogous result.

Another interesting experiment is to videotape the Autophenakistoscope. You’ll find that the frequencies of the strobe can coincide with the scanning frequency of your recorder. If you get it just right, the scope will appear to be dark in your video when it looks well-lit to your eyes.

Mechanical television

I discovered the phenakistoscope while investigating mechanical television. Mechanical television is actually very simple, but impractical except for very small screens. The scan lines are generated with a perforated spinning disk known as a Nipkow disk.

In the 1920s, television started with 24- or 32-line screens, and there were regular mechanical television broadcasts decades before Milton Berle showed his face in our (grandparents’) living rooms.

A 420-line spinning disk is another story; it would have to spin at very high frequencies to fully paint the screen at a rate that would satisfy the eye. But the Autophenakistoscope would make a great platform for a modern, experimental mechanical television. I’d also like to see it scaled up.

This project first appeared in MAKE Volume 20, page 100.