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

[JLiew.1162]

..

[Ulysses HERNIOSUS]

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]

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]

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

[Salvatore Curti]

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]

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

[JL. Lebon]

Hello,

The only way to monitor the harvested power is to place a probe on the energy harvested output of the ST25DV-I2C on the Smarttag board.

This can be done by probing the probing R6. You can monitor voltage of the energy harvesting output of the ST25DV in that point. The output voltage is a good indicator of the power strength.

Off course, this is only a "laboratory" measurement and not a real life live monitoring.

There is no "automatic" way of knowing the power transfer value from the reader standpoint, as the ST25DV cannot measure and report the power harvested.

Hope this help and best regards.

[JLiew.1162]

Dear JL. Lebon,

Thanks for the quick reply! I am assuming you are indicating of monitoring the voltage of the R6 resistor on the Smarttag board. I was wondering if I could do similar measurements with the ST25R3911B-DISCO board.

Have a great weekend and thanks for your help,

Jia Xiang Liew

[Ulysses HERNIOSUS]

Hi Jia Xiang Liew,

the received power can only be measured at the receiving side. From reader perspective you could investigate measuring Amplitude/Phase change caused by the tag. This may give you a rough indication only. Maybe you can improve if you happen to have a fixed system with known reader and known tag (geometry, matching, chip, etc.) that you characterize to find a relation of R6 voltage vs. amplitude/phase on the reader.

The other alternative would be to develop circuitry on the STEVAL-SMARTTAG, measure R6 voltage via ADC and extend the demo protocol do communicate that voltage to the reader.

Best Regards, Ulysses

[JLiew.1162]

Dear Ulysses Herniosus,

Thanks for the clarification. I would try measuring the receiving voltage via the R6 resistor with a probe and would get back to you if I have met any issues.

Have a great weekend,

Jia Xiang Liew

[JL. Lebon]

Hi,

The peak voltage on VEH pin, which will be the one you will read on R6 is dependent on the antennas size, coupling, current drawn and distance. With the smarttag antenna size, do not expect something above 3.3V.

Best regards.

[JLiew.1162]

Dear J.L Lebon,

Thanks for the quick reply! Currently, I am observing a peak voltage reading ranging from 3-10 mV. Although, I am aware that there are numerous variables that might affect this measurement.

Have a great day,

Jia Xiang Liew

[JL. Lebon]

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.

[JLiew.1162]

Dear JL. Lebon,

Thanks! Sorry what did you mean by probing either side of the R6 resistor. I had been placing probes on both ends of the R6 resistor to obtain a voltage reading.

Sorry for any confusion caused,

Jia Xiang Liew

[JL. Lebon]

Hi again,

Is your R6 resistor value different than 0 ohm ?

If this is the case, then you should probe the side which is connect to C13A. According to the schematics, this is where VEH is directly connected.

Best regards.

[JLiew.1162]

Hi again,

Thanks for the clarification! I will test out your recommendations.

Thanks again for your help,

Jia Xiang Liew

[JLiew.1162]

Dear JL. Lebon and Ulysses Herniosus,

Thanks for the advice, I was able to measure the voltages. However, I was wondering if it is possible to measure the current obtain by the RFID antenna on the STEVAL-SMARTTAG.

Thanks for your help and have a great day,

Jia Xiang Liew