Design review - B524 and a wiegand reader

Hardware
1

Hi all,
I’m starting to design a PCB to host a B524 SoM and would need to attach it to an off the shelf wiegand RFID\NFC reader.
For example:

image
image1024×682 55.3 KB

I browsed through the forum and found about the firmware that should potentilly work here and looked through someone eventually succesfully interface a reader with a Photon here.

Since I know that the B-SoM is 3.3V logic and Wiegand is 5V logic I have added a voltage level shifter (TXS0102) and capacitors + resistor as recommended by the datasheet of the TXS0102.

I also went and read this nice blog post and took some tips on the design from there (added current limiting resistors, optional pull-up resistors and ESD protection diodes).

My question, as this is a device that will be handled in the field by someone wiring it that might not be so “delicate”, is how should I protect this interface so that in case of an error the the Wiegand reader would not fry the B-SoM?

Here’s the current design, the Nets D0 & D1 connect to the B-SoM D0 & D1 respectively.

image
image1221×460 115 KB

Thanks!

2

Hi @Magrathea, the ESD protection is a must and you seem to have that covered plus you may want to consider some additional low pass filtering to prevent noise causing false triggers but be careful of impacting the rise / fall times of the signals.

The wiegand protocol is particularly edge sensitive and you will likely be using an edge triggered interrupt approach which will cause data corruption if there are unwanted noise spikes.

3

Thanks!
So basically adding a filter to filter out anything over 500-600 Hz Should be fine?
(I just read that the time between pulses is 2ms so that’s why I chose these numbers.)

4

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.