If you look at the schematic provided you will see 8 potentiometers. The value of the pots I'm using are 50k but other values higher than 5k should work. That's 8 per controller. 4 per stick and 2 per controller potentiometer. Two potentiometers are needed to calibrate one potentiometer on the joy stick. The wiring for them is pretty straight forward. Two pots have their wipers wired together and from there that junction will connect to one wiper for one pot on one analog stick. One of the outputs for one the pots that are tied together by the wiper is going to the analog stick positive side and the other pots output is going to ground. This wiring allows us to run a potentiometer acting as a variable resistor in parallel with the wiper to high and in parallel from the wiper to ground.
But what does that mean?
That means we can adjust the overall resistance of the pot on the controller from wiper to high and low by using the new parallel resistance created from the pots we added. This makes more sense if you have an understanding of how resistors behave when wired in parallel.
Why is that important?
In order to understand why that's important we need to understand what causes stick drift but before that we need to understand the workings of an analog stick in very simple terms. I cover this in my YouTube video but I will try my best to explain it in written form. An analog stick uses two potentiometers per stick to relay how the stick is being moved. A potentiometer is basically a resistor with a 3rd pin, that third pin is called the "wiper" and it moves along the path of the resistor. The wipers value changes depending on where it moves along that path. The controller uses this to create a changing voltage by moving that wiper closer to ground or closer to a positive voltage. On a perfect potentiometer you will see a resistance of 10k across both outer pins and when the stick isn't being moved you would expect a resistance of 5k from the wiper to both outputs. Even with OEM brand new sticks this resistance isn't always promised but in my experience close enough is good enough.
Are we there yet?
Almost! I swear! So now that we know the ideal resistance values of a good stick we can understand drift and how this mod accounts for it. In my video I measure a bad analog sticks potentiometer that has an overall resistance of 9.5k and from the wiper to one output we read a resistance value of 5.5k and from the wiper to the other output we see a reading of 5.3k. This difference in resistance is what causes stick drift. This can be a result of a bad pot, a stick that doesn't bounce back, breaking material or change over time. The reason why this causes drift is because the wiper of the pot is closer to one output pin rather than being centered and it makes your controller think the stick is being moved. This mod allows for that difference to be adjusted to a perfect balance by turning the pots and creating a balanced resistance from the wiper to high and the wiper to low. With the use of a game controller tester app we can easily see how adjusting the added pots affects the analog sticks drift. This part is best covered in the video, not so much in written form.
I hope I explained this well! If not feel free to ask any questions