mpr121 Arduino laptop charger noise

Other Hardware General Electronics
1

Hello everybody,

There is one problem that is bugging me for a long time, I hope some you wizard can help me!

I make a lot of midi controller with Arduino Pro micros's. if I connect my Arduino to a laptop via usb and when the power supply of the laptop is plugged in some of these instruments start to trigger buttons on its own.

Is there any way how to get rid of these noise for all laptop chargers not just the one that I have?

in the attachment there is a schematic exampel of a midi controller that uses capacitive touch and the input start triggering when its connect to a laptop with a charger, if the charger is unplugged it works as it supposed to do.

Screenshot 2019-09-26 at 12.33.32.png
Screenshot 2019-09-26 at 12.33.32.png1754×1156 333 KB

2

Try it with a NEW laptop. Old ones used high voltage AC for the screen backlight.

Have you actually traced the problem to the laptop PSU? Did you run the laptop from the battery, ONLY?

Paul

3

Paul_KD7HB:
Try it with a NEW laptop. Old ones used high voltage AC for the screen backlight.

Have you actually traced the problem to the laptop PSU? Did you run the laptop from the battery, ONLY?

Paul

The fault only happens with the charger plugged in, so its nothing to do with the screen.

This must be caused by the switching frequency leak-through on the switch-mode charger. You need to ground
the USB ground to cure this.

4

Paul_KD7HB:
Try it with a NEW laptop. Old ones used high voltage AC for the screen backlight.

Have you actually traced the problem to the laptop PSU? Did you run the laptop from the battery, ONLY?

Paul

yes it only happens when I use the laptop charger the laptop is battery has no ground loops/noise.

I use these devices in workshops and music lesson, its Annoying sometimes this USB port are acting weird. I have tried other laptops the cheaper ones have this problem but just using an another laptop doesn't solve anything. I need these to work on any application.

5

It would be wise to not use Arduino UNO with that laptop, that's not noise there's some problem with the ground. If it's an old laptop then maybe the USB jack or the power jack has missed ground.

6

MarkT:
The fault only happens with the charger plugged in, so its nothing to do with the screen.

This must be caused by the switching frequency leak-through on the switch-mode charger. You need to ground
the USB ground to cure this.

How can I ground the usb?

is there any schematic or electronic parts that can filter this so this never can happen?

Will a USB Isolator work?

7

jackthom41:
It would be wise to not use Arduino with that laptop, that's not noise there's some problem with the ground. If it's an old laptop then maybe the USB jack or the power jack has missed ground.

These are new laptops.

Wat are topics I can look up about this problem? is there a topic on how to protect Arduino sensors from noise?
Again just using other laptops is not an option.

8

janwotto:
Will a USB Isolator work?

I don't think that will help.

janwotto:
Wat are topics I can look up about this problem? is there a topic on how to protect Arduino sensors from noise?
Again just using other laptops is not an option.

Normally capacitors are used to remove noise but that won't help here. Maybe some rectifier will help here like kbp210, i am not sure though.