Vintage Computing Paper Tape Reader

Overview

This little manual paper tape reader is easy to build and operate. It connects to any modern computer via USB, and performs well with all kinds of 5 to 8 bit paper tape, including translucent paper materials. To compensate for sensor tolerances and adjust to different paper types, it can automatically calibrate its optical sensors.

Paper tape reader, fully assembled

The paper tape reader is controlled by an Arduino Pro Micro. Punched holes are detected optically, via analog inputs to the Arduino and automatic thresholding in software.

Optical readers for punched paper tape have been used since the 1950s. Non-motorized versions, where the tape is pulled through by hand, became popular with early computer amateurs in the 1970s. Oliver Audio Engineering launched the OP80A as a kit or complete unit in 1976; a replica is still commercially available today. And to this day, amateurs interested in the old paper tape format occasionally build their own optical readers.

This project takes a slightly different approach than most builds. While I also use LED & phototransistor pairs to detect the presence of holes or paper, and use the feed (sprocket) hole to trigger a read cycle, this reader does not distinguish “zero” from “one” via hardware comparators or Schmitt triggers. Instead, the on-board microcontroller (a Sparkfun/Arduino Pro Micro) reads the phototransistor currents via its analog inputs. This way it can adjust the detection thresholds in software, to compensate for tolerances between the phototransistors and to adjust to different paper materials.

The sales pitch

Gallery

Paper tape reader, handheld

Operate the reader handheld or mounted to a base plate. Tape is pulled through manually, at up to 1 meter/second feed rate.

Paper tape reader, illumination and detection module

The two main modules are the phototransistor detector (left) and the LED illuminator (right). The Arduino sits on top of the detector module. Only two power connections go to the illuminator.

Paper tape reader, individual parts

All chassis parts are made from PCB material: Circuit boards for phototransistors and LEDs, masks to precisely define the illumination and detection apertures, and light-tight spacers.