A few months ago I made a prototype punched card reader. It worked by pressing nails against the card as it was fed through the device. When holes in the card passed under the nails, the nails made contact with other nails on the other side of the card. A video of it can be found here.

There are several problems with it that might be fixable after a few prototyping iterations: the nails were at too steep an angle, the nails tended to pop out and needed to be held in with a rubber band, part of the frame had to be resized with a knife because the cogs kept getting caught, the flexible tines that held the nails in place were under constant strain and deformed over time.

An alternative card reading mechanism occurred to me, based on a pegboard with movable pegs. Movable pegs make it possible to reprogram the card without having to print or punch another one.

The photos below show a prototype. It is made using glued together parts of the earlier punched card reading prototype - this iteration is aimed at getting the dimensions right before printing out a new version.

This video shows the operation of a single sensing tine:

This video shows all four tines in place, successfully reading the state of the pegs as they pass through: