Some of the RC522 RFID reader modules, which are poor quality and generally bought cheaply, have reading and working problems. They do not read RFID Tags in the frequency range that they should be able to read, or they become inoperable without being reset after a certain working hour.
In this article, we will identify fake RC522 RFID cards and their problems and produce solutions.
Selective RFID Reader Modules
What we mean in this title is that some reader modules do not read cards, tags that are at the frequency that they should read. We can randomly define an RC522 reader as a selective reader with features such as sometimes working and sometimes not working, not working completely after long use.
The RC522 chip on the RFID Reader Module must read all 13.56 Mhz RFID cards in different models such as MIFARE Mini, MIFARE 1K, MIFARE 4K, MIFARE Ultralight, MIFARE DESFire EV1 and MIFARE Plus RF by production default. You can check this status from the datasheet
Separating Good and Bad Modules
to identify various variants of this module and classify them according to their ability to read various cards.
You can easily understand a few subtle visual differences between good and bad modules. (as well as the difference between "good" readers reading all the cards and "bad" readers reading only the cards that are supplied with them). So you can tell the difference we are talking about by looking at photos of these variants of card readers.
The next step was to find out why the "bad" modules did not read other cards that they should read. If this problem could be fixed, they could read all kinds of MIFARE/ISO/IEC14443-4 cards.
A little briefing: yes, they can be repaired. By replacing C8, C9, C10, and C11, you can solve the whole problem in one place.
Pay attention to the color of the capacitor C4, C5, C6, C7, C8, C9, C10, C11 capacitor,it is different and pay attention to the position of the silktext text of C2, R3, R4 and C3.
Bad readers use another type of capacitor, the color difference is not the cause of the problem, but it can be a good visual cue. (The difference is in the antenna coil, since the capacitors have the same capacitance" a "white" C6 equals a "brown" C6 in the capacitance.) The difference in the antenna coil is (easily) invisible.
The screen printing text position is another visual marker. Again, that's not the cause of the problem.
Small points in the bad reader (upper left and right corner) are visual differences that are a visual aid for the pick-and-place machine and do not affect the functioning of the reader (circuit board). They can also be a visual sign to distinguish between the types of RC522 readers.
In the image below can be seen the difference in the antenna coil, the copper paths are slightly narrower and further away in the bad reader. It's hard to tell that difference in real life. (But that's probably why the inductor has different characteristics)
The visual cues that stand out on this circuit board are the uncoated mounting holes, the constants next to the crystal (bottom right) and the upper left corner of the antenna coil, and the screen printing has a slightly different and brighter color. The screen printing position of C2,3 and R4 is the same as that of "good" readers, do not let this deceive you.
Here, again, these visual cues are not the cause of the problem, they are just a way to distinguish this type of RC-522 from all other types of RC-522 named RC-522.
Based on these pictures, you can try to buy "good" card readers who read all the cards. However: you do not always understand exactly what is in the picture, and these subtle differences can be difficult to withstand a claim.
Repairing Black Readers
How can bad card readers be repaired so that they can read all the cards they should be able to read?
We installed the RC522 Processor integration from bad to good, as a result the reader who was good could still read, that is, the processor integration has no problems.
We found that the antenna resonance frequency of bad readers is very low, so we need to focus on the antenna part for the problem.
The antenna is an LC circuit, so the resonance frequency can be corrected by changing the capacitance or inductance. Since the induced is fixed (the inductor is engraved on the PCB), capacitors remain. There are about 210pF (C8 + C10 == C9 + C11), this should be lower to increase the resonance frequency. For example, using 185pF works just fine.
For anyone with a good caviar, you can solve this problem with a simple method:
- Remove C8, C9, C10 and C11. This can be heated at the same time by applying a lot of soldering with hot air gun and tweezers or caviar, so that it can be shifted.
- Insert new capacitors. The C8 and C9 are each 150pF. The C10 and C11 are each 33pF. (0805 NP0, 50V). (180pF for C8 and C9 can be useful in leaving C10 and 11 blank.
After completing the transactions, you have a fully functioning RFID RC522 card reader.