Ben Eater explains how the PS/2 keyboard interface works, covering its clocked serial protocol and scancodes. He builds up the hardware-level understanding needed to read keypresses.
Why Hacker News points people here: HN commenters point to it as the clearest explanation of the PS/2 protocol, usually when keyboard interfaces come up.
There's a good video on how PS/2 works here: this video It's pretty straight-forward. There are also pre-made kits for digitizing typewriters if that interests you.
Cites itthristianJul 2021
“He investigates the PS/2 keyboard protocol”
Part of Ben Eater's keyboard protocol video series
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Piggy-backing this comment to add some context for the OP video: This "USB device discovery" video is actually the latest in a series of videos where Ben Eater is building a simple 8-bit computer on breadboards. He hooked up a PS/2 keyboard as an input device, and then got sucked into a tangent of investigating and explaining keyboard protocols. - He investigates the PS/2 keyboard protocol: this video - Somebody on Patreon asked about USB keyboards having higher latency than PS/2, so he made a video about the basic USB protocol: link - He made the OP video about USB keyboards being limited to holding six keys at once.
Cites itbear8642Sep 2021Full comment
think might be at end of this one < this video > though there's a few he's done recently on USB spec
Cites itRJIb8RBYxzAMX9uOct 2021
“Ben Eater's made a few videos discussing how PS/2[0] and USB keyboards[1] work.”
Explains how PS/2 keyboards work
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I'd imagine it would be very difficult, and would require a relatively powerful MCU. Ben Eater's made a few videos discussing how PS/2[0] and USB keyboards[1] work. USB's a vastly more complicated protocol compared to PS/2. [0] this video [1] link