ST25 NFC Tap responds with "Tag unknown"

[GKnirps]

Hi,
sorry to bother again. In the readme file it says I should use the ST25 NFC Tap app to enable energy harvesting mode or else I would not be able to run programs on the tag. I'm not that interested to run programs, but it looks like this is the only way to change the data that is transferred via NFC.

However, when I start the ST25 NFC Tap app and put the MuTag in front of the sensor, the app says "Tag unknown" and nothing else. How do I fix this?

Also: There already is data on the tag, it is this URL: https://muhack.org/events/CCC23-landing-page/. Does that mean that the energy harvesting mode has already been activated at some point?

[MrMoDDoM]

Hi,
That's kinda odd, does the same behavior appear with other phone/reader or with other generic NFC app (like this one https://play.google.com/store/apps/details?id=com.wakdev.wdnfc)? Try at least to read/write some new content to check if the memory of the NFC tag is not corrupted..

The Energy Harvesting mode is mandatory to power the MCU with only the NFC field, but it is not necessary to program the MCU nor to read/write NFC Tag.

Before the CCC23 I manually wrote on every tag an URL to some landing page, but I did not activate the Energy Harvesting mode as it require some non-automateble steps that as single person working on this project I didn't have time to do ;)

[GKnirps]

Hi,
thanks for the reply, and sorry for my rather sluggish responses (I currently have a lot of things going on).

I have no google playstore on my phone, so I always have to jump through hoops to get Apps on the phone that don't exist elsewhere, but with the wakedev app you linked to I was able to write some data to the tag. I'm happy that worked, so I can start to actually use the tag (even though I won't have fancy LED stuff).

[MrMoDDoM]

Excellent! I was worried that something bad happened to your tag, but seems that it is still operational after all..

Anyway, there should be a way to activate the Energy Harvesting mode via I2C commands from the MCU by setting the correct system configuration register, but frankly I didn't investigated much such method as the official App was a better and quicker way to achieve the same goal..

In the datasheet ( https://www.st.com/resource/en/datasheet/st25dv04k.pdf ), in the section 4.3 System configuration area , the register in question is the third, namely EH_MODE ( better described in the Table 35. EH_MODE ).

You could create a little script to just read the current status of that register and then write a new value: maybe you could also send a pull request once done 😄

Hope this help!