Many of us remember back in our school days taking tests and filling out answers on a Scantron sheet, those long rows of A, B, C, D, and E that had to be filled in with a #2 pencil. Ever wonder why it needed a #2 pencil, or what the point of using a Scantron was at all? That question is answered in the latest video from [SimonRetro], where he takes a look at the Scantron and how it works.
One of the more interesting things about the Scantron is that it’s such a standalone device. No software needed, no keypad to mess with just two rocker switches. The on/off switch is also the way you tell it to forget the last answer sheet and allow you to program in a new test. Upon booting, you feed in a Scantron sheet with some specific boxes filled in, and then it’s programmed and ready to take in and grade all the students’ answers. Opening up the Scantron reveals it’s pretty interesting inside: one control board with early-’90s-era chips. There’s also a lightbulb (no LEDs) shining through the six reading sections of the card, as well as an arrangement of belts and motors to move the card through the machine. The printer is a seven-pin printer used in conjunction with a pair of ink rollers to print out the results on the cards.
[SimonRetro] also went ahead and tried different ways to mark the sheets including pens, Sharpies, colored pencils, and different thicknesses of pencils besides the #2 to see which would and wouldn’t work in the Scantron. Thanks [SimonRetro] for exploring this machine from many of our childhoods and sharing its inner workings. Be sure to check out some of our other reverse engineering articles that explore how classic devices work.
