Error 87 issue while reading tag using CR95HF-VMD5T NFC transceiver chip.

[BGome]

Hi,

We have developed a NFC reader design using the CR95HF-VMD5T chip. Our design is similar to the X-NUCLEO-NFC03A1 development board, its just we have used a flex NFC antenna by PulseLarsen with part number W7001.

The issue we are facing is that the board is unable to read a tag and returns error 87, with the firmware we have written.

We have tested our firmware on the X-NUCLEO-NFC03A1 development board and we are able to read a tag without any problem.

We also probed the antenna pads of both our board and X-NUCLEO-NFC03A1 using an oscilloscope just to see if we see any difference in the signal. What we noticed was that the X-NUCLEO-NFC03A1 board was showing a 10V peak-to-peak sine wave at 13.5Mhz whereas our board was showing around 3.4V peak-to-peak around the same frequency.

We wanted to know if this is the reason for our problem and a solution for that or if something else is going on that we're missing.

I have attached the antenna's datasheet for reference.

Thanks

Brosnan Gomes

Hardware Developer Engineer

+917972046516

Mrinq Technologies

[Brian TIDAL]

​Hi Brosnan,

if I understand correctly (please confirm), you plan to use a cable between the output of the matching circuit (called ANT1 and ANT2 in your schematics) and the flexible antenna?

In that case, you will have to take into account the capacitance of the cable in the matching circuit.

There are different possibilities for the cable depending on price, mechanical and EMC constraints:

• unshielded or shielded twisted pair
• coax

At least an unshielded twisted pair should be preferred to a simple 2 wires.

Rgds

BT