[AVR] NFC interference to the controller board

Hi all,
I have a "lock door system" project using the NFC reader PN532 with the microcontroller ATMEGA328P-PU.
I already finished the circuit and software of the project, when I test it I face some problems, the NFC reader make an interference to the controller board, the reader freeze the controller and stop its process.
after some test I see that I should move the reader away form the controller board, so I redesign a new board to do this, now I force new problem, now the board is restart when I use the NFC card !!!
also after some more test, I found that when I use an extension cable (of length more than 16 cm) between the board and the reader the system work so far so good. (I tried with lower length cable but it wasn't work)!

so how to solve this problem?!
how to eliminate this cable?! or what is the equivalent component of this extension cable?!

any help appreciated
thank you

Sounds like a problem of bad circuit layout with large ground loops, insufficient power supply bypassing or similar. The problem can be easily solved with a four-layer PCB and a continuous ground plane, a two-layer layout must be well considered but should work, too. Can you show layout photos, hardcopies or gerber data?

FvM said:

Sounds like a problem of bad circuit layout with large ground loops, insufficient power supply bypassing or similar. The problem can be easily solved with a four-layer PCB and a continuous ground plane, a two-layer layout must be well considered but should work, too. Can you show layout photos, hardcopies or gerber data?

Click to expand...

attached the PCB layout

The PCB layout is not well designed. It is designed using Proteus (ARES).

pic.programmer said:

The PCB layout is not well designed. It is designed using Proteus (ARES).

Click to expand...

true, what is the problem with that?!

I recognize a single-side PCB with jumpers.

The least you can do to improve it's RF hardness is to place bypassing capacitors (e.g. 100 nF ceramic) directly between ATmega power supply pins and ground, 7-8 and 20-22. Either small conventional with shortest possible leads or SMD caps.

Secondly there may be a problem with the RESET pin. I don't see what's the function in your circuit, e.g. dWIRE or SPI serial download support? If it's not absolutely needed, you can disable it in fuse settings. Otherwise it should be blocked with a smaller cap (e.g. 1 nF size) to ATmega GND pin.

Another possible solution could be to place a magnetic shield under the board, a metal sheet or copper clad PC substrate.

Thank you for your help Mr. FvM

I am going to design a new 2 sides PCB, and i will fill the empty space by ground (continuous ground plane).and i will add two 104 ceramic capacitor to the controller PS.
for the reset problem, bellow is my Reset circuit. but I don't understand what is the function you ask for?! if you mean what is the communication between the reader and the controller, so yes it is SPI. knowing that I am using RTC module which is using the I2C protocol.