topic Re: MPR121 PCB Layout in Sensors

MPR121 PCB Layout

2dom — Sat, 20 Sep 2025 06:34:38 GMT

Hi all,

I created what I thought is a very simple design of a MPR121 touch button matrix. But for some reason I cannot get it to register any touches. Any help would be highly appreciated. (See board and schematics attached)

Dom

Re: MPR121 PCB Layout

2dom — Sat, 20 Sep 2025 10:53:40 GMT

I am using the standard arduino mpr121 library with auto configuration and some debug output:

08:36:16.760 -> send soft reset.. 08:36:16.760 - read: MPR121_CONFIG2 24
08:36:16.760 - write Configuration to sensor ...
08:36:16.826 - MPR121 found!
08:36:16.924 - Initial CDC/CDT values:
08:36:16.924 - ========================================
08:36:16.924 - CHAN 00 01 02 03 04 05 06 07 08 09 10 11
08:36:16.924 - -- -- -- -- -- -- -- -- -- -- -- --
08:36:16.924 - CDC: 0 0 0 0 0 0 0 0 0 0 0 0
08:36:16.924 - CDT: 0 0 0 0 0 0 0 0 0 0 0 0
08:36:16.924 - ========================================

Re: MPR121 PCB Layout

TomasVaverka — Mon, 22 Sep 2025 07:04:34 GMT

Hello Dominic,

The MPR121 is no longer manufactured and supported by NXP.

Resurgent Semiconductor (Flip Electronics) has received the manufacturing rights for the MPR121 and I recommend reaching out to their technical support:
https://www.flipelectronics.com/Product/MPR121QR2-53295

Thank you for your understanding.

BRs, Tomas

Re: MPR121 PCB Layout

2dom — Thu, 25 Sep 2025 21:45:50 GMT

Thanks for letting me know. I think I found the problem - the MPR121 appears to be rather sensitive to high soldering temperatures. The hot air gun simply cooked the chip. Using a temperature controlled hot plate for soldering did the trick.