Analog Stick Interference / Ghosting?

[MrGeekFreak]

Expected Behavior

Analog addon will allow two sticks to operate simultaneously without interference.

Current Behavior

When using the Analog addon, pressing a direction on either analog stick causes occasional detection on the other - even when the second analog stick is not wired up. I have tested a Sparkfun Analog stick breakout, a SJ@JX PS2-style (using Hall-effect potentiometers) joystick, and a SJ@JX arcade analog stick - all exhibit the same behavior.

Context

Model: Pico-Plus RP2040 Advanced Breakout Board USB Pico Fighting Board Game Controller Board GP2040, small, blue
Link: https://www.amazon.com/dp/B0D3FKHJWK

I am using a Fightbox RP2040 Advanced Breakout Board v5.3E flashed with GP2040-CE v0.7.10-2-g230983f. I previously tried the firmware the board shipped with (I think 0.7.9?), and updated it due to running into this issue. The issue persists on the update.

All other wired buttons into the top green screw-terminal headers function without issue, only the analog sticks wired into pins 26-29 experience the interference / ghosting.

Steps to Reproduce

1. Wire in the analog sticks outputs to pins 26-29.
2. Wire the analog stick voltage-in to VCC.
3. Wire the analog stick ground to the option port grounds.
4. Enable the Analog add-on using the web configurator.
5. Reboot the board into controller mode.
6. Test inputs using Steam Controller settings or various emulator input setup screens.

Screenshots & Files

Video Example of Input Interference / Ghosting:
https://github.com/user-attachments/assets/1ebc981b-337a-40f1-a56c-24bde66a593b
This video was captured while moving the right analog stick when the left was completely disconnected.

[MrGeekFreak]

I ordered a V5.6E GP2040-CE from FocusAttack to see if the issue persists across different boards (indicating I am doing something wrong), I will keep this issue updated once it arrives.

[MrGeekFreak]

I figured it out. It seems the VCC voltage was varying too much - using the filtered 3V3 output on the Expansion Port for the analog sticks resolved the issue!