this post was submitted on 12 Aug 2025
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Big keyboard jack, serial for mouse, parallel for printer
Don't forget the serial input for gamepads and joysticks in the dedicated sound board for some reason
Except that wasn't a serial port, it was midi, and the reason it was on the sound card was because the input was analog.
Your joystick was just two fancy potentiometers, and your soundcard decoded the voltage on the middle legs into a position.
Soundcards handled joysticks because they had the fastest ADCs.
They didn't even use an ADC. They used 555 timers to produce a pulse. They measured the length of the pulse to determine the potentiometer position. Since there are 4 analog inputs, they typically used the 558 timer which is the quad version of the 555.
And here I thought I had it all figured out. But it does make sense. Doing it with an analog signal introduces noise and measuring pulse widths is going to be simpler.
I don't know what I'm going to do with this information but I'm glad it's in my brain now.