Advice for a problem with N64 analog stick modding

hebble

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Feb 2, 2023
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Hey,
I have a question about N64 pad hacking I am hoping I can get answered here, or least some direction on.

My current project is to create a fight stick for playing AKI wrestling games on the N64.

The games use the D-pad for movement and allow of the button, which are all straight forward to wire up to arcade buttons and joysticks. The trick part is that the games require the player to push the analog stick in any direction to execute a taunt. Taunting is a key game play mechanic as it enables the player to enter a special state from which signature moves can be executed.

Here is the fight stick I want to put the padhack into
IMG_1446.jpg

Ideally I would like some kind of control where the 24mm start button is located on the ride side. But after extracting the pad, wiring up all the buttons, and getting to the analog control I realise I was pretty naive sticking this project. Initially I thought I could bridge some pins on the analog input with a momentary switch. Pressing the button will increase an axis value, but releasing the button does not decrease it (of course) so the wrestler gets stuck in a taunting state as the axis value does not return to neutral.

I have since done some research and I am hoping it is possible to wire up a potentiometer to one of the axis. As the N64 sets the initial position of the analog stick as neutral when powered on, I figure the potentiometer's initial position would 0,0 and moving it would make it 0,100 for a taunt then turning to the initial position would be back at 0,0. Even better if the potentiometer is spring loaded to go back to 0,0 (Maybe this doesn't actually exist as I can't find one online)
I don't have a potentiometer to test at the moment.

But after more reading, I am not sure if the CNT-NUS chip will accept the potentiometer's signal? Nintendo uses optical sensors to determine the sticks position an sends back two signals for each axis, YA YB and XA XB, where as potentiometer only sends back one, maybe. I don't really know.




I get the feeling it would be better to use a third party pad that has potentiometers by default. That would be cheaper that a N64 Stick Converter PCB V3 or a teensy 4.1 running USB64.
I guess in that case the potentiometer would be from -100 to +100 on the axis and would need to return to twelve o'clock to be at 0. Likewise the other axis may need the appropriate resitor to lock it at 0.

You can probably tell I am pretty lost at the moment, so any ideas or input would be appreciated.

TL;DR. How can I create an input that mimics pushing an analog direction and then returning to neutral?
 

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hebble

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Alright, so thinking about this some more..

I don't think I need a potentiometer, just a change in resistance that resets with a button push. I am taking a complete guess here, but maybe a circuit like this may get me where I need?

curcuit2.png


I am completely unsure if I need both XA and XB activated by a switch, either separately or combined.

I am planning to test it out when I have time. Though now I think a need a breadboard to make prototyping easier.

One thing I worry about is that while poking around I bridged two pins on the analog stick connector and the N64 shutdown. When I tried powering it on, it wouldn't until I had left it for a good while. Any idea what combination of pins might have done that? I guess VCC and something else, feeding too much voltage down the wrong path. Anyway, I am hoping I don't fry the N64 permanently in pursuit of this crazy idea.

Hacking a third party controller which uses potentiometers already seems like the path of least resistance ( no pun intended )
 
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hebble

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Sorry to keep posting to my own thread like this, but Its been a few days and I have a development.

I decided to go the route of hacking a third party pad instead. I chose a Yobo pad because it obviously had a gamecube/psx type stick, so I figured it would definitely have pots instead of optical sensors. And... jackpot!

The wiring matches this diagram by ShockSlayer in this old thread https://bitbuilt.net/forums/index.p...for-oem-n64-controller.1031/page-2#post-11553


I added a button to bridge the two x wires like so
IMG_1841.jpg


Pressing the button changes the x value enough to trigger a taunt, and releasing it returns to normal. Happy lad.
The resting resistance of the pot, a.k.a. neutral, is 20K ohms. So I can remove the stick completely and just wiring in some resistors to maintain the neutral state of x and y.
I just wired up a button directly and it works fine, no need for resistors. lol


I won't update until I am finished or something else comes up, but I want to say this forum has been valuable. Not only as a source of info and inspiration, but also as a platform for me to rubber duck this problem. Cheers
 
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