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Good day all,

I am wanting to know the maximum number of RC522 RFID modules that can be successfully connected to one RPi 4 B with multiplexer/s using SPI interface.

The RC522 RFID modules are only required to read RFID/NFC cards not write.

Only one module at a time would need to be utilized.

There will be an external 3.3v power supply.

RC522 RFID module

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  • Ah, let me see. I read the product sheet: (1) "RC522 RFID Module - Components101, 2019jun12": components101.com/wireless/rc522-rfid-module, and have the following observation, conclusion, and recommendation. /to continue, ...
    – tlfong01
    Nov 18, 2020 at 4:17
  • I read my old post：electronics.stackexchange.com/questions/517428/… just now to refresh my memory. I think the RC522 device is selected by the SS pin. So (1) If you are using Rpi4B with 5 on board SPIs, you can try selecting up to 5 SPI devices, (2) ／　ｔｏ　ｃｏｎｔｉｎｕｅ，．．．
    – tlfong01
    Nov 18, 2020 at 4:34
  • Ｔｈｉｓ　ｉｓ　ｍｙ　ｏｌｄ　ｐｏｓｔ　ｏｎ　ｔｅｓｔｉｎｇ　４　ｒｆｉｄ　ｃｈｉｐｓ　ａｔ　ｔｈｅ　ｓａｍｅ　ｔｉｍｅ：　raspberrypi.stackexchange.com/questions/109773/…．
    – tlfong01
    Nov 18, 2020 at 4:51
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    You can connect as many as you want.
    – joan
    Nov 18, 2020 at 9:05
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    You need 500 pins that can be used as CS line, then even a single SPI bus is enough (although of course you can only talk to one module at a time). Using a bunch of 16-Port GPIO expanders (such as MCP23018) should get you quite far.
    – PMF
    Nov 18, 2020 at 12:40

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