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Analog Thumbstick Questions


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#1 ArugulaZ

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Posted 11 December 2008 - 08:57 AM

A couple of months ago, I made a modular fighting game controller by pulling the chip out of a Sega Saturn joypad, soldering thin wires to the bare traces, then soldering a 15-pin connector to the other end of the wires. The plan is to make this controller compatible with as many other game systems as possible, particularly consoles with stock joypads that don't lend themselves well to old-school gaming.

I've already got it working with the GameCube, the Wii (through the GC port), the Nintendo 64, the 3DO, and now I've adapted it to the Xbox 360 by tearing apart a MadCatz Arcade Pad and using that as an adapter. The MadCatz Arcade Pad doesn't do many things well, but it's great for hacking projects because the button pads are very large, plus it uses a common ground.

It took a couple hours of soldering and testing, but I got the controller working pretty well. Thanks to this site, I was even able to wire up the left and right trigger buttons, which is something I couldn't figure out on my own. The finished controller instantly boosted my score in games like Street Fighter II Hyper Fighting and Pac-Man Championship Edition, but more importantly, it made those games a lot more enjoyable.

As great as this controller is, I'm still not quite satisfied with it. I want to get the analog thumbsticks in on the action... maybe add a port for an Atari paddle so I can play games like Tempest and Space Giraffe. The MadCatz Arcade Pad does have a primitive spinner on it, but anyone who's used it knows that it pretty much sucks... an Atari paddle would be a much better way to go.

There's just one problem, though. I'm not sure how the six pins on the analog thumbstick work. I presume they work like potentiometers, but why are there three pins for each axis instead of two? Shouldn't it be just voltage and ground? If you could explain to me how the analog thumbsticks work, I'd really appreciate the assistance. I'm dying to spin my way to higher Space Giraffe scores!

#2 RDC

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Posted 11 December 2008 - 12:20 PM

How many Potentiometers have you seen that had only 2 pins?

Voltage, Wiper, Ground. The POTs are 10k, like a 10k Resistor between Voltage and Ground, then the Wiper is the signal line the controller IC 'reads' to know where the stick is at. When the stick isn't touched the Wiper is in the center and the voltage divided evenly (it's not that precise but for illustration sake it is) then when pushed in one direction it's closer the Voltage rail and more voltage is on the signal line, pushed the other way it's closer to Ground and less voltage is on the line. There's 2 POTs per stick also for both axis, an X-axis (left/right) and Y-axis (up/down).

#3 ArugulaZ

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Posted 11 December 2008 - 11:24 PM

QUOTE(RDC @ Dec 11 2008, 06:56 AM) View Post

How many Potentiometers have you seen that had only 2 pins?


On the Atari 2600, only two of the three pins on the potentiometer are connected.

#4 RDC

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Posted 13 December 2008 - 03:33 AM

QUOTE(ArugulaZ @ Dec 11 2008, 06:00 PM) View Post

On the Atari 2600, only two of the three pins on the potentiometer are connected.

Still, that's not a 2 pin Potentiometer though. wink.gif

Is it only wired up to two of the pins or is the 3rd pin wired to one of the others? What value is it also?

#5 ArugulaZ

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Posted 13 December 2008 - 11:53 PM

QUOTE(RDC @ Dec 12 2008, 10:09 PM) View Post

Still, that's not a 2 pin Potentiometer though. wink.gif

Is it only wired up to two of the pins or is the 3rd pin wired to one of the others? What value is it also?


Only two of the pins are wired... the third pin isn't connected to anything. The value of the pot is one megaohm, so it offers a lot more resistance than the 10K of the Xbox 360 analog thumbsticks.




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