how many rfids can operate in series

good afternoon I have a project to connect multiple rfid to a mega arduino card, I have connected 6 readers, but the reading is not constant since the communication of one or two readers is lost

led.ino (6.27 KB)

pullup_resistors present? (range 3k..10k)
sorry. - my miss

knut_ny:
pullup_resistors present? (range 3k…10k)

Pullups for an SPI bus?

I have connected 6 readers, but the reading is not constant since the communication of one or two readers is lost

How long is you SPI bus? The library communicates at 4MHz. A bus length > 50cm probably won’t work reliably, even if everything is in a shielded case.

Explain why you need 6 RFID reader so close together. If you describe your project in more detail we may find a better solution.