Please help in eliminating ground loop for my Arduino Mega MIDI Drums Project

I'm a newbie to electronics and programming. I've built a 16pcs electronic drum kit using Arduino Mega, 16pcs 27mm piezo transducers, via Hairless MIDI USB serial bridge using Superior Drummer 2.0 as my drum module software. It is a basic circuit with just piezos with 5.1v zener diodes and 1M resistors in each piezos. It is working pretty good, almost comparable to the pad sensitivity of Roland VDrums series BUT only when my laptop is running on battery. If I play drums while my laptop is connected to power (wall outlet) the piezo tends to double trigger specially when hitting the pad harder. I've tried to increase the piezo threshold from 10 to 20 it fixes it but it sacrifices sensitivity to soft hits not allowing me to play buzz rolls. The pad I've made is made of 10mm thick plywood that I've cut into circular shape approximately 7 inches in diameter with 10mm thick rubber mat glued on top as a padding and to provide stick bounce. It is already my final make since making some more adjustments with the wood and padding thickness does not make things comfortable for me. Everything is fine if I play drums with my laptop only running on battery. I am aware that unused analog pins should be connected to ground, but it is still the same when using all inputs or having unused inputs connected to ground. This problem only happens if my laptop is connected to power so I'm thinking that this has something to do with ground loop since I am having a similar problem when connecting a USB audio mixer to my laptop, it produces a little static, buzzing noise that only happens if the laptop is connected to power, does not matter if I use a different laptop. And its also manifested by ringing effect when touching the brass side of the piezo that only happens when my laptop is connected to power. If someone can help me fix this ground loop issue with my Arduino Mega MIDI Drums Project I would greatly appreciate it, I've already spent several months trying to find a solution. Please help.

How have you got your piezos wired and how long are the leads from the elements to the controller?
Are your leads shielded?
Do you tie all their gnd to one point or daisy chain.

Can you post a picture of your project?

Thanks… Tom… :slight_smile:

Thanks for replying Tom. Hmmm… I feel so stupid now that you asked how I made the circuit and the leads/wire. You will be surprised how messy it is. I’m too shy to show my circuit but I guess I have no choice, I really want to eliminate the annoying ground loop problem.

Please see attached photos…

The piezos are attached to the center of each pads underneath the wood, I soldered them to an RCA jack, so I use a long speaker wire with RCA plugs on both ends to connect the piezos to arduino. The RCA jacks that are soldered to inputs A0-A15 are all connected to common ground.

2017-01-06 18.54.29.jpg

Hi, The project looks really good mate. The enclosure is not metal so that might be a bit of a problem. I would use shielded cable on all you piezo leads and internal wiring, shielded microphone cable would do the job.

If you unplug the piezo, does the hum disappear?

Tom... :)

Oh.. Sorry if I've confused you with my very long explanation of the problem, There is no problem with hum, static or any unwanted noise.. Its just that when I'm playing drums while my laptop is connected to power the piezo double triggers specially if I hit the pad hard, it would give me a max midi velocity (127) then followed by 15 or sometimes less, even though I only hit the pad once. It only happens when my laptop is connected to power.. Everything is fine if I play the drums when my laptop is on battery. And also, when my laptop is connected to power, if I touch the brass side of the piezo, it will make the midi note ring, this never happens when my laptop is on battery so I really think it is due to ground loop. I will try to do what you have suggested. I will also try to use a metal enclosure. Thank you.

Hi, Grounding discussed on THIS INCOMPLETE PAGE

,, I'm working on it; not ready for prime time...

Thanks for this very helpful page. Very detailed. I will try all your suggestions and I'll get back to you guys.

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