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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

J01010
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  • Ah, let me see. I read the product sheet: (1) "RC522 RFID Module - Components101, 2019jun12": https://components101.com/wireless/rc522-rfid-module, and have the following observation, conclusion, and recommendation. /to continue, ... – tlfong01 Nov 18 '20 at 04:17
  • I read my old post：https://electronics.stackexchange.com/questions/517428/thm3060-rfid-reader-setup-issues 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 '20 at 04:34
  • Ｔｈｉｓ　ｉｓ　ｍｙ　ｏｌｄ　ｐｏｓｔ　ｏｎ　ｔｅｓｔｉｎｇ　４　ｒｆｉｄ　ｃｈｉｐｓ　ａｔ　ｔｈｅ　ｓａｍｅ　ｔｉｍｅ：　https://raspberrypi.stackexchange.com/questions/109773/how-can-rpi-spi-python-read-the-mfrc522-nfc-module． – tlfong01 Nov 18 '20 at 04:51
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    You can connect as many as you want. – joan Nov 18 '20 at 09:05
  • In practical terms, how would I go about connecting 500 modules to run in the way I have described? – J01010 Nov 18 '20 at 12:14
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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 '20 at 12:40

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