Detect presence of an NFC card using the PN512 ADC I/Q Channels

[user_leo]

Hello,

As a low power option, I am attempting to detect a card using just the readouts from the ADC I and Q channels which are done by reading Register 0x3B. 

However, the only read out I get from it is 0xF0 after the field is turned on. Before that the readout is 0x88. There seems to be no discernible difference between the readouts when there is a card vs when there isn't a card. 

I was able to successfully use the provided libraries Ex1 Discovery Loop to detect NFC cards using the pn512 over SPI and sending the WakeUp command but because there is so much overhead I am just trying to detect the presence of a card using the ADC I/Q channels only that way I don't have to turn on the pn512 for as long. Basically trying to do Low Power Card Detection with the PN512. 

Thank you 

[EduardoZamora · Accepted solution]

Hello @user_leo

Perhaps the only approach I could suggest you is to put the host processor to sleep and wake it up at periodic intervals to turn the RF Field ON and scan for tags.

Please, explore the possibility of moving your development to one of the latest focus products from our NFC Readers portfolio, as these devices support Low Power Card Detection, and they could help you speed up your development and avoid implementation issues.

I apologize for the inconvenience.

Regards,
Eduardo.

[user_leo]

Hello again!

I see that is unfortunate. I thought I read that the LPCD was performed by detecting detuning via the ADC I/Q channels on the newer NFC chips and hoped to do something similar with the PN512. 

Regardless,

Thank you for the reply. 

[user_leo]

Edit: Attached is an image of some log messages which show the ADC value read from register 0x3B and whether a card was detected or not.