Hi! I was wondering if there is an application to test the signal strength between ST25R3911B Disco and STEVAL-Smarttag1. Many thanks.

JLiew.1162 · ‎2021-02-01

JL. Lebon · ‎2021-03-09

Hello,

The schematics of the smartag are available at: https://www.st.com/content/ccc/resource/technical/layouts_and_diagrams/schematic_pack/group0/cb/fb/57/2f/d3/54/4a/b8/STEVAL-SMARTAG1_schematic/files/steval-smartag1_schematic.pdf/jcr:content/translations/en.steval-smartag1_schematic.pdf

If you look at the schematics, R6 resistor is directly connected to the VEH output via the HARV signal. As it is supposed to be fitted with 0 ohm, you can probe any side of R6. This VEH pin itself is very difficult to access on the ST25DV-I2C (U3) as the package is very small and pins are below the package and only visible on the side of the package. You can also probe on the right side of C13A or on D1.

If you want the real value that comes into the regulator (U1), then you should probe after D1 and you should see the diode voltage drop.

Best regards.

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Ulysses HERNIOSUS · ‎2021-02-01

Hi JLiew.1162,

what do you exactly understand by "signal strength"?

The strength of the reader field? I assume for this you could measure on STEVAL-Smarttag1 the received voltage on its antenna using a scope or measure the harvested power. Maybe the STEVAL-Smarttag1 has some internal diagnostic here - would need to consult the experts here.

There is also the opposite direction where you could observe on ST25R3911B the strength of the observed load modulation - using a scope on RFI pins or by looking at Gain Reduction state + RSSI display registers after a reception from the tag.

Best Regards, Ulysses

JLiew.1162 · ‎2021-02-01

Dear Ulysses Herniosus,

Thanks for the quick reply. I was interested in measuring the harvested power on the opposite direction on the ST25R3911B. To clarify, a scope would be used to measure the voltage on RFI pins?

Have a great day,

Jia Xiang

Ulysses HERNIOSUS · ‎2021-02-01

Hi Jia Xiang,

If you want to verify the signal strength you need to observe the difference between modulated and unmodulated of the tag. When the tag is answering this will become visible. In case of STEVAL-Smarttag1 with its ST25DV this will be a 424kHz subcarrier which is used for a Manchester coding.

Just measure the voltage difference between those two levels.

Alternatively the ST25R3911B will have some information for relative comparison also in its mentioned registers: Gain Reduction state + RSSI display of the ST25R3911B. Inside our rfal you will find function rfalGetTransceiveRSSI() which can combine the two registers into one value.

Best Regards, Ulysses

JLiew.1162 · ‎2021-02-01

Dear Ulysses Herniosus,

Thanks. Regarding, the rfalGetTransceiveRSSI() function is there a step by step process (documentation) to retrieve these values. As I am new to this platform and am not sure how it is done.

Yours Sincerely,

Jia Xiang

Ulysses HERNIOSUS · ‎2021-02-01

Hi Jia Xiang,

We don't have a step by step documentation for this feature but in the end it is as simple as reading those two registers after a reception. Inside the ST25R3911B-DISCO GUI you could issue some commands on ISO15693 tab (best to not use Inventory as it disables AGC und uses slotted protocol) and after the response observe these two registers inside the register map.

For doing it from software you may use e.g. X-CUBE-NFC5 and issue the mentioned function call after having read data from the tag (e.g. after rfalNfcvPollerReadSingleBlock()).

Regards, Ulysses

Ulysses HERNIOSUS · ‎2021-02-02

Hi Jia Xiang,

you wrote "interested in measuring the harvested power on the opposite direction on the ST25R3911B". I guess I was not reading fully your comments. I apologize! The RSSI and measurement on RFI of ST25R3911B don't relate to the harvested power but only to the strength of the modulation.

I am not aware that the STEVAL-Smarttag1 will indicate the currently received power to the reader. But I let the tag experts comment about the available options.

Best Regards, Ulrich

JLiew.1162 · ‎2021-02-02

Dear Ulysses Herniosus,

Thanks for the quick reply! Hopefully I would be able to hear from the tag experts soon.

Have a great day,

Jia Xiang

Salvatore Curti · ‎2021-02-04

Hi JLiew,

I can only suggest you to see this web page:

https://www.st.com/en/evaluation-tools/st25r3911b-disco.html#tools-software

Regards,

Salvatore Curti

JLiew.1162 · ‎2021-03-04

Dear Salvatore Curti and Ulysses Herniosus,

Thanks! I hope someone from the ST community could provide me more technical details and methods on how to measure the harvest power/ signal strength. Would I be able to monitor the read and write rate as an alternative option? (If so, how would I be able to do that?)

Many thanks,

Jia Xiang Liew