Unhelpful Documentation: Capacitive Sensor low-level library - Anomaly 84

RE: Unhelpful Documentation: Capacitive Sensor low-level library - Anomaly 84

Einar Thorsrud — Mon, 25 Mar 2019 13:16:34 GMT

Yes, the library works well on the desk. It definitely can work. The main problems are:

The ISOURCE (used for relaxation oscillator) as a way too high temperature variation.
The library has a simple calibration mechanism. It might not work properly under varying air humidity etc, which influences the capacitance.
Lack of testing
The library is not much used (if at all)

RE: Unhelpful Documentation: Capacitive Sensor low-level library - Anomaly 84

awneil — Mon, 25 Mar 2019 12:56:38 GMT

[quote userid="7377" url="~/f/nordic-q-a/45270/unhelpful-documentation-capacitive-sensor-low-level-library---anomaly-84/178063"]the capsense SDK libraries should be considered proof of concept[/quote]

So far, so good:

photos.app.goo.gl/4nYP4NFJd66ukNGz8

(that's an nRF52-DK, and using an Atmel QT1-XPro board just to provide the touch pads).

RE: Unhelpful Documentation: Capacitive Sensor low-level library - Anomaly 84

Einar Thorsrud — Mon, 25 Mar 2019 11:55:36 GMT

[quote user="awneil"]And so it seems that Ole Bauck's answer here was wrong?[/quote]

Yes, what he said is wrong. The "fix" for nRF52840 was to remove the ISOURCE altogether.

RE: Unhelpful Documentation: Capacitive Sensor low-level library - Anomaly 84

awneil — Mon, 25 Mar 2019 10:55:40 GMT

[quote userid="7377" url="~/f/nordic-q-a/45270/unhelpful-documentation-capacitive-sensor-low-level-library---anomaly-84/178063"]none of the nRF52 devices have a functional ISOURCE[/quote]

That makes it even worse!

😮

That really does need to be clearly & explicitly stated!

And so it seems that Ole Bauck's answer here was wrong?

RE: Unhelpful Documentation: Capacitive Sensor low-level library - Anomaly 84

Einar Thorsrud — Mon, 25 Mar 2019 10:37:09 GMT

Hi,

I agree with you awneil (sadly).

[quote user=""]But there is no indication of where or how to find out the current status of this "Anomaly 84" ![/quote]

The reason you only find references to erratum 84 in the nRF52832 is that the ISOURCE feature was removed from the COMP peripheral on the other nRF52 devices. Since it is not in the product specification for those, it is also not documented that it is not working. But the bottom line is that none of the nRF52 devices have a functional ISOURCE.

[quote user=""]How much "less accurate" is the SAADC implementation? What is the practical upshot of this?[/quote]

Well, this statement was probably based on having a functional ISOURCE, which is not the case. It should be disregarded.

[quote user=""]Bottom line: Is it usable?[/quote]

Maybe, with the SAADC approach, depending on your requirements. But the capsense SDK libraries should be considered proof of concept only. I will create an internal ticket regarding the documentation, requesting that it be updated to clarify the limitations of the SAADC libraries in the SDK.

RE: Unhelpful Documentation: Capacitive Sensor low-level library - Anomaly 84

awneil — Fri, 22 Mar 2019 19:21:51 GMT

Sure, we can waste time googling and eventually dig up the answer - but that really shouldn't be necessary!

😞