Issues initializing SPI connection between MFRC522 reader and nRF52840 dongle

RE: Issues initializing SPI connection between MFRC522 reader and nRF52840 dongle

Einar Thorsrud — Wed, 19 Nov 2025 11:28:33 GMT

Hi,

I see the user in the thread you linked to got it working with theNRF52832 in the project he shared, and I see no reason why it should not work with a nRF52840 dongle then. But debugging is needed in order to understand what is happening. I suggest you obtain a debugger (could be a DK) and a simple logic analyzer so that. you can understand what is happening in the nRF and on the SPI lines.

I would expect that the only thing you wold need to do to use that project on an RF52840 dongle is to make an overlay file for the dongle (in the same way as is there for the nRF52 DK). That should at least be a good starting point as that is reported as working with the same peripheral device, and all nRF52 devices are very similar so it does not matter much that this was with an nRF52832.

RE: Issues initializing SPI connection between MFRC522 reader and nRF52840 dongle

Bitti_1 — Tue, 18 Nov 2025 19:19:11 GMT

https://devzone.nordicsemi.com/f/nordic-q-a/108235/i-am-trying-to-communicate-with-nrf52832-on-mrfc522-vscode-my-write-and-read-functions-are-not-working here's a link to a problem some one had with the MFRC522 earlier. Im using he's example from GitHub. Should it work with the nRF52840 dongle ?

RE: Issues initializing SPI connection between MFRC522 reader and nRF52840 dongle

Bitti_1 — Tue, 18 Nov 2025 17:17:34 GMT

here you can see the files and configures im using atm:

devzone.nordicsemi.com/.../134521.main.c devzone.nordicsemi.com/.../0207.MFRC522.c devzone.nordicsemi.com/.../5078.MFRC522.h

RE: Issues initializing SPI connection between MFRC522 reader and nRF52840 dongle

Bitti_1 — Tue, 18 Nov 2025 15:33:48 GMT

Hey Einar,

Unfortunately i dont have debugger that i could hook into the dongle. The application is running till this point i can see from terminal:

Could the problem be how the RST or CS is handled? Cant figure out how to configure them...

RE: Issues initializing SPI connection between MFRC522 reader and nRF52840 dongle

Einar Thorsrud — Mon, 17 Nov 2025 14:34:22 GMT

Hi,

I do not have any experience with RC522 and we do not have explicit support for it, but you should be able to communicate with it over SPI and use it as I see is done in the Github repository you linked to.

The next thing should be to debug to understand what is going on. Do you have a debugger you can hook up to the dongle? If not, an alternative is an nRF52840 DK, which has an onboard debugger (that is a better development platform in itself, and can also be used to debug the dongle).

As you see data on MOSI the nRF is clearly attempting to communicate with the slave (RC522). Is there any data being read back? Have you analyzed the data sent from the nRF to see if it is valid for the RC522? This will be easier to check if you have a logic analyzer that can analyze SPI and show you the data. Also, have you checked basic connections?