X-NUCLEO-NFC05A1 calibrate capacitive sensor not working.

[JOBri.2]

I'm using a X-NUCLEO-NFC05A1 (on a Nordic nrf5340 dev kit board), and want to enable/test Capactive Wakeup. Before enabling, I'm trying to perform direct command 0xDD Calibrate Capacitive Sensor. According to the data sheet, this should be performed while in Power Off mode, and the an interrupt will be generated on termination.

I never see any interrupt generated, I'm expecting to see an IRQ due to termination of direct command. How long should calibration take? I've waited for up to 10s, still no interrupt.

Any suggestions on things to look at/try to get this working?

Normal power on mode NFC reading of Type 2 tags works fine.

[Ulysses HERNIOSUS]

Hi JOBri.2,

I am still investigating why the I_dct would not happen. However you can just wait for cs_cal_end bit or wait for 3ms and then check cs_cal_err.

Please make sure cs_mcal=0 for it to operate!

Regards, Ulysses

[JOBri.2]

Hi Ulysses,

Indeed, I do see cs_cal_end bit set, even though I'm not seeing I_dct.

A couple more questions:

Would it be normal for cs_cal0 - cs_cal4 to be 0 after calibration ends?

Do you have any suggestions for starting values for cm_d0 - cm_d3 (diff to reference to trigger I_wcap)?

Thanks,

--Jim

[Ulysses HERNIOSUS]

Hi Jim,

in most cases you will end up at a calibration value of 0. You may see different values when you bring in major changes of capacitance.

About the cm_d: It needs to be a trade-off between reactivity and noise resistance. We advise values of at least 2 (with a value of 1 you can always find environment where the value is between two values and jumping randomly).

You may even need to go above 2 as capacitive wake-up is in principle more susceptible to external noise and environmental changes than inductive wake-up.

To the point of I_dct you need to rely on cs_cal_end/time as I found a statement in ST25R3916 DS which says that I_dct is only generated while in Ready mode and not in Power Down mode. It seems the update of DS of ST25R3911B is pending.

Regards, Ulysses