IEEE Spectrum breed · Technologie

Scanwheel: A Portable Wide-Screen Electromechanical TV

The Scanwheel is a pocket-sized, wide-screen electromechanical television with a resolution of 4,096 by 20 pixels, developed as an evolution from clock-making. It utilizes a 3D-printed drum with holes that pass over LEDs, controlled by a Raspberry Pi Pico and its programmable input/output (PIO) coprocessors.

Electromechanical television, pioneered by John Logie Baird in the 1920s using a Nipkow disk, was the first practical form of television. While cathode-ray tubes replaced this technology, hobbyists continue to build and innovate upon it. This project draws inspiration from plenoptic cameras and volumetric displays, aiming to reverse the process to create light fields.

Instead of a Nipkow disk, the Scanwheel uses a Nipkow drum where holes are arranged in a stair-step pattern along the cylindrical surface. This design allows for horizontally aligned digits and enables a smaller drum diameter compared to a disk for the same number of scan lines, facilitating a portable design. The device uses five light sources, initially conceived for a clock display, which can function as a single wide screen.

The high horizontal resolution, currently at 4K and tested up to 8,000 pixels, is achieved by rapidly modulating LED brightness. Despite its low vertical resolution (20 pixels), the Scanwheel can display legible digits and even stream video.

The Raspberry Pi Pico's RP2040 microcontroller, with its four PIO coprocessors, is crucial for managing the spinning drum and simultaneously modulating the five LEDs, including a color LED. The PIO handles most of the I/O tasks, allowing the CPU to focus on setup. Video data is streamed to the Pico via a network interface, enabling it to mirror a computer screen or act as a separate display.

The 3D-printed casing and drum are customizable using an OpenSCAD file available in the project's GitHub repository, allowing users to adjust parameters for different drum heights or other modifications for their own portable electromechanical displays.

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