nRF5340 - real-time time capture

RE: nRF5340 - real-time time capture

Einar Thorsrud — Tue, 11 May 2021 07:26:22 GMT

Hi,

Now I see. I was mostly focusing on the first line of your question, if you get a quadrature encoded signal which you typically get from something measuring rotation, then QDEC is definitely sensible.

Regarding the QDEC on the nRF53 that is at least partially supported in NCS master. There, HAS_HW_NRF_QDEC0 is defined, and that is equivalent with HAS_HW_NRF_QDEC (See CONFIG_NRFX_QDEC).

RE: nRF5340 - real-time time capture

Gabriele — Mon, 10 May 2021 14:00:02 GMT

Thank you Einar.

The aim is to measure instant flow and volume of air.
Our encoder is a low inertial vane rotating in between two swirl plates deflecting the air entering the air flow path and converting the linear airflow into a helical flow. The vane angular velocity is proportional to the flow and is detected by the interruption of a pair of infrared beams.
Thus we have two signals which are pulse trains in quadrature.
The frequency of each pulse train is therefore proportional to the air flow and the number of pulses is proportional to the volume.

QDEC is ready-made to immediately deliver the volume by counting pulses, with automatic adjust of count direction upon reversing of flow.
The approach you suggest is measuring the flow, by assessing time between consecutive pulses.
At first glance I would say it is more complicated, for the fact that you have to use three objects (GPIOTE, TIMER, DPPI) instead of one (QDEC).

RE: nRF5340 - real-time time capture

Einar Thorsrud — Mon, 10 May 2021 12:33:17 GMT

Hi,

Just out of curiosity, why does using QDEC make sense in this case? You would normally use GPIOTE and a TIMER hooked up via DPPI in such cases, for instance as shown here (some minor adjustments are needed for the nRF53140).

RE: nRF5340 - real-time time capture

Gabriele — Mon, 10 May 2021 09:06:17 GMT

Hi,
I think nRF5340’s QDEC peripheral could be great to solve my problem.
From link
I see Zephyr manages the quadrature decoder.

The next question is how to activate it under NCS 1.5.1 ?
I’ve enabled CONFIG_QDEC_NRFX in prj.conf, and put the following definition in dts overlay

&qdec {
    status = "okay";
    a-pin = <3>;
    b-pin = <28>;
    enable-pin = <30>;
    led-pin = <0xFFFFFFFF>;
    led-pre = <0>;
    steps = <24>;
};

Build fails in parsing the input tree.
From link
I read nRF5340 is not listed among the SoC allowed to enable HAS_HW_NRF_QDEC.

Is there a way to use QDEC on nRF5340 ?