ST25R95 0x87 Response from SENDRECV

[PDIhawk]

I am in the final stretch of my project using the ST25R95 with an ATTINY88.  I am working on custom hardware and not using libraries.

I have all of the ST25R95 related commands working on my development setup with an Arduino UNO and X-NUCLEO-NFC03A1 but I moved to the custom hardware and I am not able to read a tag.

I used the EMI Filter Calculator to determine the values for the EMI filter and matching circuit.  Measuring with a spectrum analyzer, I have a higher level of output at 13.56 MHz than the NUCLEO dev board.  So my matching must be pretty good.

I have attached the SPI trace from boot to the SENDRECV REQ command to wake the ISO14443-A tag but I get a 0x87 response.

Any ideas?

[PDIhawk]

I am still stuck on this problem.

I might have figured out how to capture the SPI with the IRQ IN and OUT.  Please take a look and see if the attached CSV is helpful.

Thanks!

[PDIhawk]

It appears that I was wrong about my matching and having enough signal on the RF.  After re-measuring the X-NUCLEO board and the custom board, I was sigificantly lower ~20dB.

After measuring from ST_R0 to TX1 and TX2, I was below a volt.

The EMI Filter Calculator didn't really work out for me.

I have been working to tune my circuit and I'm betting I will be up and working after that.

[Brian TIDAL]

Hi,

can you share your schematics and your EMI calculation spreadsheet so that we can have a look?

Rgds

BT

[PDIhawk]

Hi Brian,

I have attached my EMI calculation spreadsheet and a schematic that has place holder values just so I had a footprint on the board and I knew I would figure out the values later.

Currently the schematic has:

560nH for L1 and L2

100pF for C16, C17, C20 and C21

R9 is a 330Ω

Started with 33pF at C13, C14, C22 and C23 to get around the 67pF that the calculation tool tells me to use.

Started with 180pF at C18

I am using Pulse Electronics W7002 antenna.

I was getting around 3Vp-p at the antenna leads.  I was able to get the output up 23Vp-p by pushing C18 all the way down to 27pF but it didn't make it read tags.

[Henry Crane · Accepted solution]

Hi,

first step is to validate the antenna tuning circuit (some frequency drift can exist between the calculation sheet and actual input impedance because of non predictable parasitic capacitance). the procedure is to measure the antenna impedance, calculate and implement components based on desired input impedance (I guess 50Ohm in your case), measure the antenna matching circuit input impedance between  10 and 20MHz and adjust components values based on drift between measurement and calculation.

could you share the antenna impedance measurement and the antenna tuning circuit input impedance with the calculated components (please see AN5248 in case not already done)?

Once antenna tuning circuit validated, activate the ship setting RF ON and check voltage across 1nF capacitor that should be connected on ST_R0 as recommended in AN5248. 

best regards,

Henry Crane NFC/RFID product Support team.