As you specifically ask to share experiences with detecting bad boards I'm posting this issue.
Unfortunately it is a negative result, but I hope it's still worth sharing.
We had a set of 4 readers deployed, 2 could read both Mifare cards and Desfire cards (we're only interested in the ID, not in Desfire-specific functionality). 2 could only read Mifare cards and didn't detect Desfires at all. Modules were bought from different sources over the last 10 years or so.
Visual inspection showed absolutely no difference between the boards. Introspection (chip version, telemetry, etc): no difference.
Tried many different things, like sweeping over transmit power, receive amplification, more. No success whatsoever. So in the end we've settled on trial and error: test a board and if it doesn't work throw it away.
Full findings are available at cwi-dis/iotsaDoorOpener#5
As you specifically ask to share experiences with detecting bad boards I'm posting this issue.
Unfortunately it is a negative result, but I hope it's still worth sharing.
We had a set of 4 readers deployed, 2 could read both Mifare cards and Desfire cards (we're only interested in the ID, not in Desfire-specific functionality). 2 could only read Mifare cards and didn't detect Desfires at all. Modules were bought from different sources over the last 10 years or so.
Visual inspection showed absolutely no difference between the boards. Introspection (chip version, telemetry, etc): no difference.
Tried many different things, like sweeping over transmit power, receive amplification, more. No success whatsoever. So in the end we've settled on trial and error: test a board and if it doesn't work throw it away.
Full findings are available at cwi-dis/iotsaDoorOpener#5