"why are people so obsessed with making things for calculators?"
It's a computer.
I don't see why you are against learning the how computers operate.
This PDF right here shows you the very basis of data transfer for 2.5mm (as well as 3.5mm) link cables. Yes, I tested it with calculators, but because they're mini computers that are easily editable and the hardware is directly accessible through software.
They're great devices for learning how computers work.
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