I am making a drum controller using Pro Micro (to play Taiko Drum Master). By using Leonardo-Switch-Controller library, I have realized controling NS. For sensor, I used Piezo electric discs. One side connected to Arduino GPIO, the other side connected to GND. In NS Handheld mode, my drum worked well. But in TV mode (that is, the Pro Micro's USB is directly connected to The Nintendo Switch Dock), I did't play the drum, while Pro Micro was frequently triggered automatically.
By oscilloscope, I found that, in TV mode, Pro micro's GPIO will received 800mV noise (Vpp, to GND)(when not beat the drum). But in Handheld mode, the noise only ~40mV. In PC mode, ~20mV.
Is the failure caused by the unstable voltage output of The Nintendo Switch Dock? For my Pro micro, the power and signal ground are shared.
Anyone can told me how to solve the problem? I would be very grateful for your help!
Schematics showing grounds, power and signal would surely help to get an overview.
Thank you for your advice. Below I provide more circuit information.
This is the schematic of the Pro micro. My 4 piezos' signal connected to A0~A3, piezos' GND connected to Arduino's GND. Current limiting resistors are connected in series to the piezos' signal line. The pull-down resistor connects the signal line to GND.
The core of my problem is: Why my Pro micro's GPIO have a big noise (Even without connecting anything) when USB plugging into The Nintendo Switch Dock. And how to solve it.
Thanks.
You tell about different modes but being ignorant about what the difference is, I have no clue.
Where is the piezo device in the schematics?
In Handheld mode, my Pro Micro powered by Console. In TV mode, my Pro Micro powered by Nintendo Switch dock. Perhaps these two websites will make things clearer 
.
In fact, I've got to the root of the problem, but I can't solve it.
When Pro micro powered by Nintendo Switch dock, Pro micro's GPIO has a big noise (~0.8V Vpp) all the time(It's the same when Pro micro not connected to any thing). When Pro micro powered by Console, the value is 0.04mV.
Nintendo Switch dock's USB port make my Pro micro'GPIO getting noise signal all the time. I don't know why and How to fix it.
That raises only more questions having no experience of those devices.
Have You measred the Vcc? Maybe adding some cap to it would bring down the noise.
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