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NYC Resistor’s phooky built a punchtape reader to read some old punchtapes. After an initial attempt, he built a new reader:

This time I used proper phototransistors and IR LEDs I scrounged up around the space (thanks, Miria and Raphael!). Because they’re 5mm in diameter (and the spacing between channels is only 2.54mm), I had to come up with a new sensor packing. This one reads bits from four separate columns over a space of five columns, requiring an internal buffer of five columns to reconstruct a single column of data. Even so, the spacing was tight, and I had to sand down the flanges of the phototransistors and LEDs to make everything fit. I milled simple PCBs for both sides to keep things nice and neat, and used a small surface-mount potentiometer to limit the current to the LEDs in case the paper wasn’t thick enough to block enough light. The light mask is made of black acetal this time, and the spacers include runners to help keep the tape straight. There’s still no automatic feed mechanism, but we now have a reader that’s fast and reliable enough to read tapes in earnest.

phooky has a github repository with his design files.

John Baichtal

My interests include writing, electronics, RPGs, scifi, hackers & hackerspaces, 3D printing, building sets & toys. @johnbaichtal nerdage.net


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Comments

  1. Byron Winchell says:

    I wonder if fiber optics could have used to manage the packing problem. Probably would have made for a bulky machine.

  2. Chrisw says:

    I still have a punch tape which has ASCII art of Santa and his sleigh. I got it from our timeshare provider in the early 70′s.

  3. PaulG says:

    How did the original punch tape readers work? Were they optical, or did they use some other mechanism? (piano rolls use pneumatics, for example)

    My memory of paper tape was from travelling to Alaska with my father when I was eight. As a private pilot, he would have to check in at the Flight Service Stations before filing flight plans, and they used teletypes with paper tapes for the weather reports.

  4. Rahere says:

    The IBM ones we used in the 60s were mechanical, using lightly-sprung feeler probes about the size of a hair pin and a metal contact.

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