Mechanical TV

Before all-electronic TV, there was mechanical TV - Systems which used a single photocell and a whirling perforated disk, lenses, or mirrors to scan a small spot across the image. These systems could only produce low resolution, on the order of 30 lines (about the same resolution as a Windows icon, 32x32). Pushed to the practical limit, these systems might have reached 120 lines at most, and were superceded by electronic scanning means.

Some hobbyist experimenters these days are adapting modern solid-state photocells, transistor circuits, and LEDs for use with the old mechanical techniques, and have even restored phonograph recordings of the old signals.

Read more about it at these links.

Some photos of original mechanical TV gear at the Henry Ford Museum, Dearborn Michigan: