NFC not working on custom board

RE: NFC not working on custom board

SK — Fri, 14 Dec 2018 01:10:53 GMT

okay sure, will keep that mind. Thanks!

RE: NFC not working on custom board

ketiljo — Thu, 13 Dec 2018 10:07:15 GMT

Good that you found the cause. Note that the pins may be damaged if you use them for NFC while setup as GPIOs. That's why they are set as NFC as default. If you see any problems, replace the chip first just in case.

RE: NFC not working on custom board

SK — Thu, 13 Dec 2018 01:23:59 GMT

Hi ketiljo,

Attached, you will find 2 images from the oscilloscope (1 for the DK and the other for custom board). Yellow line indicates the differential voltage between NFC pins.

Unfortunately, we were not able to find the center frequency since we do not have of either of the instruments required to carry out the tuning methods. 😞

But, after debugging much, i saw that NFCPINS register had GPIO enabled. (I had configured NFC pins to GPIO before and i thought that by just removing the macro CONFIG_NFCT_PINS_AS_GPIOS would make them NFC pins again. I was wrong to think that way.

Configured the pins back to NFC antenna pins by erasing uicr register and doing a system reset. Now the NFC works fine. 😃

Thanks for the help!!

RE: NFC not working on custom board

ketiljo — Mon, 10 Dec 2018 10:38:07 GMT

Ok, so the oscillator is not the problem then.

When the NFC module is active, you should see a little less than VDD/2 on NFC1 or NFC2 with reference to ground.

So you see the same voltage swing on the DK and on your board?

Have you changed anything from the DK design? Is the antenna physically the same or have you made it on the PCB? Can you check the center frequency of the antenna with one of the two methods shown in the whitepaper?

RE: NFC not working on custom board

SK — Mon, 10 Dec 2018 06:10:54 GMT

Hi ketiljo, I tried by configuring LF clock source to 32KHz RC oscillator and followed steps given here as well -> https://devzone.nordicsemi.com/f/nordic-q-a/15363/change-clock-source-nrf52832-app-beacon-example

This did solve the invalid param error mentioned above, but NFC is still not working. :(

RE: NFC not working on custom board

SK — Mon, 10 Dec 2018 01:47:42 GMT

Yes, we have 32KHz crystal on our board. And looking at the sdk.config.h file, it's using XTAL clock source.

// <0=> NRF_CLOCK_LF_SRC_RC
// <1=> NRF_CLOCK_LF_SRC_XTAL
// <2=> NRF_CLOCK_LF_SRC_SYNTH

#ifndef NRF_SDH_CLOCK_LF_SRC
#define NRF_SDH_CLOCK_LF_SRC 1
#endif

If i change the value to 0 to have RC clock source, ble_stack_init() throws an Invalid param error. :(

Looking into the ble_app_hrs_nfc_pairing example, i found the value of LF_SRC to be 1 too.

RE: NFC not working on custom board

ketiljo — Fri, 07 Dec 2018 13:00:38 GMT

Do you have a 32 kHz crystal on your board? The DK has one so if you don't and haven't configured your FW to use the 32 kHz RC oscillator, it will fail.

If the antenna is identical, you could use the same capacitor values

RE: NFC not working on custom board

SK — Fri, 07 Dec 2018 09:08:35 GMT

Thank you ketiljo for that link. However, after discussing this with the electronics design guy, he told that we are using the same values for the capacitance as those on the nRF52 DK (PCA10040 board). We are using the same antenna which comes with DK too.

Will it not show the same behavior if we are going to use exactly the same values and antenna? Please advise.

Another question that i had here is that if the antenna frequency is not tuned, then when we bring the smartphone in the NFC range, should there be any spike in the voltage? I ask this because i see a spike in the voltage level on the oscilloscope when i try to pair via NFC :(

RE: NFC not working on custom board

ketiljo — Fri, 07 Dec 2018 08:24:24 GMT

Have you seen this? http://infocenter.nordicsemi.com/pdf/nwp_026.pdf It could be as easy as the antenna isn't resonating at the correct frequency.

RE: NFC not working on custom board

SK — Fri, 07 Dec 2018 06:26:59 GMT

Hi, i have also set CLOCK_ENABLED to 1 as mentioned in some of the forums here, but still NFC is not detected.