Supercon Badge Reads A “Punch” Card

David Beckam

This 12 months’s Hackaday Supercon, the primary since 2019 because of the pandemic, was once an excessively equivalent affair to these of the previous. Virtually each and every hardware-orientated hacker match has its personal customized digital badge, and Supercon was once no other. This 12 months’s badge is a simulation platform for a hypothetical 4-bit CPU created via our personal [Voja Antonic], and introduced an actual problem for probably the most attendees who had by no means touched gadget code all the way through their youth. The problem set was once to get a hold of probably the most fascinating hack for the badge, so collaborators [Ben Hencke] and [Zach Fredin] set about nailing the ‘expandr’ class of the contest with their optical punched card reader bolt-on.

Peripheral connectivity is slightly restricted. The speculation was once to construct a bolt-on board with its personal native processing — the use of a PixelBlaze board [Ben] introduced alongside — to take care of all of the scanning main points. Then, as soon as this system at the card was once learn, sell off the entire thing over to the badge CPU by means of its serial interface. With out get admission to to theirPrinted paper faux punch card showing read LEDs and an array of set and reset bits of the encoding same old amenities again house, [Ben] and [Zach] clearly needed to improvise with no matter they’d with them, and no matter might be scrounged off different badges or different {hardware} mendacity round.

One giant factor was once that the general public don’t typically elevate photodiodes with them, however thankfully they remembered that an LED can be utilized as a photodiode when reverse-biased accurately. Feeding the sign advanced over a one Meg resistance, right into a transconductance amplifier courtesy of a donated LM358 there was once sufficient variation for the STM32 ADC to reliably hit upon the variation between unfilled and crammed check-boxes at the filled-in program playing cards.

The CPU required 12-bit opcodes, which clearly implies 12 photodiodes and 12 LEDs to learn every phrase. The PixelBlaze board does no longer have this many analog inputs. A easy trick was once as a substitute of getting discrete inputs, all 12 photodiodes had been stressed out in parallel and fed right into a unmarried enter amplifier. To distinguish the other bits, the illumination LEDs as a substitute had been charlieplexed, thus turning in the person bits as a series of values into the ADC, for next de-serialising. The demonstration video presentations that it really works, with a program loaded from a card and kicked into operation manually. Such amusing!

Punch playing cards typically have a hollow thru them and can also be learn routinely, and are a good way to configure testers like this fascinating vacuum valve tester we coated a twinkling of an eye again.

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