PC Engine 6 button controller

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lilshawn:
just a thought... i haven't perused your schematic much but your circuits behavior seems to indicate a floating or otherwise not properly pulled input causing random behavior.

typically in circuits, you tie an input line high through a 10k pull-up resistor to drive it definite high... then yank it low through your switch. i see some 47k resistors, perhaps the value is too high and not driving up the input of the chip high enough above the 0/1 switch point threshold.

check the Vil(max) and Vih(min) of your chips datasheets to make sure your high and low states with a voltmeter and see if it's within the ranges specified. (typical 74 series logic has a "0" in the 0.8v and under range and a "1" in the 2.0v and up range... and anything between 0.8 and 2.0 produces 0/1 random gitch switchingness)

something worth looking into anyways.

pbj:
I had another electronics engineer look over the circuit. I’ve only been feeding and inebriating his ass for 25 years. His comment was similar - the 47k pull ups seem too high. And he thinks my capacitor addition is filtering noise. His suggestion was a 10k array. Perhaps those circuits were all 4.7k and nobody noticed the typo for 35 years?

I tried another capacitor value while I had the box of them out - 220pF and it was the same behavior as 100pF.

I did some play testing tonight. Some games are 100% playable in 2 button mode - Dragons Curse, Alien Crush, Devils Crush.

Some will immediately throw a select input when the level starts, but otherwise play normally - Shinobi, Rondo of Blood.

SF2 plays fine, but it brings up a “define buttons” screen before each match and also skips the between round trash talk scenes. Just like smashing the select button would do. In both 2 and six button mode.

I did notice on most games that pressing select made the character have a down input.

I am so tantalizing close on this one…. But even as-is I’m having fun with it.

:cheers:

pbj:
Well, I tried a 10k resistor on select. No change. Then I added the 100pF capacitor. No change.

:dunno

lilshawn:
honestly, I would go down as low as 1k on that circuit. you aren't worrying about fighting another circuit pulling it high/low there, might as well pull hard.

I've gone as low as 470 ohms on some projects just to get the Vih(min) high enough that it doesn't randomly trip the input. (especially on a microcontroller's unused reset line which benefits from being driven high to keep it from randomly resetting due to shenanigans.)

mourix:
I've been chasing the resistor arrays for the most of these posts. 47k makes sense for short pcb traces but for long wires it may not.

1k too low though. Every button you press would pull 5ma from the PC engine which adds up if you push many at the same time. If 4.7K does not work and 1K does, there are different issues than your pull value.

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