How can a purely mechanical mechanism distinguish between holes and non-holes in the tape, without deforming/ripping the paper, and then effect a larger difference depending on the sensed bit with more mechanical energy?
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2$\begingroup$ Have a look at the pedal vacuum powered piano roll mechanism: pianola.com/ppworks.htm. $\endgroup$– TransistorCommented May 13 at 23:00
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3 Answers
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The original punchcard mechanism as used on looms they pushed a set of rods through the card. A weak enough spring will allow the rod to push against the card without damaging it. And then a simple micro-switch mechanism can detect the difference between hole and not-hole.
Another option is to have a set of contacts on both sides of the card (one of the spring-loaded). Then when there is a hole there is electrical contact, when no hole the contacts are insulated from each other.
Other than mechanical or light, one could also use compressed air (or a vacuum) with a channel going to a piston, like used in mechanized instruments (for example a self-playing piano).
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Back in 1974, 50 years ago, my high school had a couple of Model 33 teletypes (teleprinters) connected to a DEC PDP 11/70 computer. The paper tape readers they had were mechanical ones which fingers, or rods, that felt the holes in the paper tape. They were noisy. So was the teletype!
Different companies made different types of paper tape readers, but the most common were mechanical fingers, or optical devices. Optical devices were faster and quieter.
One had to be careful with paper tape because if it was mechanically read with fingers because, with repeating reading, eventually the paper would degrade and the paper would break. When this happened a new paper tape would be cut.
One convenient way to store paper tape, so it wouldn't get damaged while in storage was to use small cylindrical plastic containers. My computer studies teacher at the time, used to keep smaller length roles of tape in plastic containers that used to contain Kodak 35 mm photographic film for SLR cameras.
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The punched tape readers collected the data by shining a light through the holes with sensors to record the patterns.
You can get an overview here: https://gcodetutor.com/fanuc-training-course/punch-tapes.html
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$\begingroup$ That is simpler/faster but I have heard it mentioned (here for example: youtube.com/watch?v=JafQYA7vV6s) that there existed, and for the purpose of this question am only interested in, purely mechanical ones $\endgroup$– 2080Commented May 13 at 7:50