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Plans for uploading reference design for Capactive Touch applications?

Hello, deavteam. This is MANGO.

The Capacitive Touch on the nRF52 series blog post is really impressive.

I'm planning to start a haptic driver project using TI's DRV2605 driver, an LRA (Linear Resonant Actuators), and Nordic's nRF52 MCU in the 4th quarter of 2018 or 1st quarter of 2019.

EVM

The DRV2605EVM-CT evaluation board provided 6 capacitive circle buttons.

Replacing the MSP430, which is populated on the evaluation board, to the nRF52 for my custom PCB is my main objective.

Although the erratum 84 (COMP: ISOURCE not functional) sound daunting to me,

I think there might be a chance for that anomaly to be fixed and see a button sensor reference design that has

Pad

SNR

  • low power consumption

  • low Parasitic Capacitance (Cp)

  • SNR (ratio of capacitive touch signal to noise) greater than or equal to 5:1

  • Annular gap (the air gap between the sensor and ground) considering decreased noise immunity

  • Hatch ground fill, connected to a ground shield, to reduce the Cp (surrounding the sensor + PCB bottom layer)

Since nRF52 supports NFC-A, a feature required for my project, choosing other Bluetooth chip vendors is not an option for me.

in short,

  1. Just like the GitHub nRF5 reference design, are there any plans to upload an Eagle/Altium design project on GitHub to demonstrate a reference design for capacitive touch applications?

  2. Is there any news about the erratum 84? If that anomaly can be fixed,

users might expect 2 reference design; RC charge timing / Relaxation oscillator application design

  1. If there are plans to create the reference design, can a tutorial be provided together to create the touch sensor layout using EAGLE or Altium?

EAGLE doesn't allow copper to be placed in a device footprint, except for SMD pads. If you try, DRC will complain about it.

I had difficulties handling the layout, so I was curious how the deavteam handles this problem.

-Best regards, MANGO

  • Hi,

    1. The Touch sensor PCBs used in the blog post were not made by Nordic. If you look at the images you can google their serial numbers to find them. Not sure if you will find layout files though.

    2. Unfortunately there are no immediate plans of fixing erratum 84. We recently released a second revision of the nRF52832, but other errata were prioritized.

    3. As mentioned the PCBs weren't our designs, but I'm sure you will find other layouts and tutorials online showing you how to make touch buttons.

  • Thanks for your time, Martin. I am referring other vendors' capacitive touch PCB designs.

    One of the concern is that I don't have tools to measure Parasitic Capacitance and SNR after creating a capacitive touch PCB. Additionally, I was doubtful whether I can receive supports if I open a "MyPage Case" later on. So I was hoping to see a reference design from Nordic.

    4th quarter of 2018 / 1st quarter of 2019. Plus, this is not an urgent project for me. So I thought maybe there could be some timeslots to both of us; me working with capacitive touch / devteam fixing the erratum 84 or creating a reference design.

    Although you cannot assert the revision plan for erratum 84, hope to hear a plan for that later on. Also, does Nordic accepts this type of "MyPage Case" support?

    -Regards, MANGO

  • I suppose measuring the capacitances is useful, but I guess each sensor needs to be calibrated in software at application startup anyway (and probably every once in a while after that).

    In MyPage we are happy to do review of components and design directly related to our ICs, their matching network and antenna.

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