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

[awneil]

The Capacitive Sensor low-level library documentation says:

Note:

Until Anomaly 84 (ISOURCE not functional) is fixed, the COMP solution cannot provide production-level quality. Use the SAADC solution instead.

But there is no indication of where or how to find out the current status of this "Anomaly 84" !

Further unhelpfulness:

Using COMP gives more accurate results than SAADC

How much "less accurate" is the SAADC implementation? What is the practical upshot of this?

Bottom line: Is it usable?

[Einar Thorsrud]

Hi,

I agree with you awneil (sadly).

But there is no indication of where or how to find out the current status of this "Anomaly 84" !

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.

How much "less accurate" is the SAADC implementation? What is the practical upshot of this?

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

Bottom line: Is it usable?

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.

[awneil]

Einar Thorsrud said:

the capsense SDK libraries should be considered proof of concept

So far, so good:

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

[Einar Thorsrud]

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)