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

[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

[JLiew.1162]

Dear Ulysses Herniosus,

Do you what is the expected peak voltage when measuring the R6 voltage?

Have a great day,

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

[JLiew.1162]

Dear JL Lebon,

Thanks for the quick reply! Could you clarify where the VEH pin is located on the board? I am currently measuring the peak voltage across the R6 resistor with probes attached.

Many thanks,

Jia Xiang Liew

[JL. Lebon · Accepted solution]

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