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We have designed an HMI, which will contain a 10.1" TFT with PCAP touch panel.

I am using an enclosed power supply to convert the 230V AC to 12V DC. Only DC positive and negative is connected to my board.

I have noticed that when I use to draw over the LCD, the processor will not detect some of the coordinates. I couldn't reproduce the same issue in another building of my company, which lead me to suspect the earthing of the building.

I found the issue in my workplace. Finally, I found that the earthing in my workplace is not proper. When I found out the earthing issue in my workplace, I gave a separate earth connection to my power supply chassis, snd the touchpanel worked fine without any issue.

From the above point, I assumed that the issue is occurring with the noise on power rail - mainly common-mode noise.

In this scenario, I solved the issue by giving proper earthing. But I can't expect all others to provide proper earthing. (Most of the building earthing will be proper, but there is also a chance it may not OK.)

Can anyone suggest a way to suppress this noise in my board without earth connection?

I already tried with different common-mode chokes, but it didn't come out well.

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  • \$\begingroup\$ Try connecting the DC negative terminal of your supply to the nearest earth(if exists to the supply's mains earth pin). You cannot get rid of CM noise entirely without routing the CM currents back to earth. \$\endgroup\$ – Genzo Feb 14 at 13:48

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