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I'm trying to solder a TTP223 capacitive touch sensor to a USB switch (specifically a "UGREEN USB 3.0 Switch, 2 In 4 Output") to rig a sort of capacitive KVM switch to a desk PC I'm building, however I'm having trouble with it. It seems that when I connect the VCC and IO ports to the switch, it takes two presses of the button to work and I'm not entirely sure why. I've tried the same thing with a DisplayPort switch (CABLEDECONN DisplayPort 8K DP 1.4 Switch) and it works fine.

Apologies if I've missed any important details, this is my first real dive into anything electronics based, so I'm not even really sure how to go about debugging it. I haven't connected the ground wire to anything, and I'm not sure if it should be. Does anyone have any ideas of what may be the issue, or how I go about testing things?

Below I have a picture of the board that does work: DisplayPort Switch

and the one that doesn't: USB Switch

EDIT: I've tested both boards with a multimeter, and the voltage over the DisplayPort board is 3V whereas the USB has 5V. I'm guessing this has an impact, but I'm not really sure what to do about it.

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    \$\begingroup\$ What Cs value did you choose? \$\endgroup\$ – Tony Stewart EE75 Feb 27 at 14:24
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    \$\begingroup\$ What do the various data sheets tell you about this? \$\endgroup\$ – Andy aka Feb 27 at 14:27
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    \$\begingroup\$ @Andyaka I have the datasheet for the TTP223 button (components101.com/admin/sites/default/files/component_datasheet/…), but can't really see any information as to why two presses would be required. As for the other two chips, I can't find any data sheets on them unfortunately, I'm guessing because they're proprietary. \$\endgroup\$ – ktx Mar 1 at 9:48
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    \$\begingroup\$ I think you should add some capacitance reduce the bounce \$\endgroup\$ – Tony Stewart EE75 Mar 1 at 14:58
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    \$\begingroup\$ The wires in the first pic appear to have cold solder joints. \$\endgroup\$ – Lundin Mar 2 at 14:50

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