We may be a bit biased, but the storage media of yesteryear has so much more personality than that of today. Yes, it’s a blessing to have terabyte SD cards smaller than your pinky nail and be able to access its data with mind-boggling speed. But there’s a certain charm to a mass storage device that can potentially slice off your finger.

We’re overstating the dangers of the venerable paper tape reader, of course, a mass storage device that [David Hansel] recreated a few years back but we only just became aware of. That seems a bit strange since we’ve featured his Arduino-based Altair 8800 simulator, which is what this tape reader is connected to. Mechanically, the reader is pretty simple — just a wooden frame to hold the LEGO Technic wheels used as tape reels, and some rollers to guide the tape through a read head. That bit is custom-made and uses a pair of PCBs, one for LEDs and one for phototransistors. There are nine of each — eight data bits plus the index hole — and the boards are sandwiched together to guide the paper tape.

The main board has an ATmega328 which reads the parallel input from the read head and controls the tape motor. That part is important thanks to Altair Basic’s requirement for a 100- to 200-ms delay at the end of each typed line. The tape reader, which is just being used as sort of a keyboard wedge, can “type” a lot faster than that, so the motor speed is varied using PWM control as line length changes.

Thanks to [Stephen Walters] for the tip.

When the job at hand is measuring something with micron-range precision, thoughts generally turn to a tool with a Mitutoyo or Starrett nameplate. But with a clever design and a little electronics know-how, it turns out you can 3D print a displacement sensor for measuring in the micron range for only about $10.

While the tool that [BubsBuilds] came up with isn’t as compact as a dial indicator and probably won’t win any industrial design awards, that doesn’t detract from its usefulness. And unlike a dial indicator — at least the analog type — this sensor outputs an easily digitized signal. That comes courtesy of a simple opto-interrupter sensor, which measures the position of a fine blade within its field of view. The blade is attached to a flexure that constrains its movement to a single plane; the other end of the flexure has a steel ball acting as a stylus. In use, any displacement of the stylus results in more or less light being received by the phototransistor in the opto-interrupter; the greater the deflection, the less light and the lower the current through the transistor. In addition to the sensor itself, [Bub] printed a calibration jig that allows precision gauge blocks or simple feeler gauges to be inserted in front of the stylus. The voltage across the emitter resistor for these known displacements is then used to create a calibration curve.

[Bub] says he’s getting 5-micron repeatability with careful calibration and multiple measurements of each gauge block, which seems pretty impressive to us. If you don’t need the digital output, this compliant mechanism dial indicator might be helpful too.

Thanks to [Bub]’s friend [Ethan] for the tip.