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I am doing a project using an Arduino and a Rfid Mfrc522 module, both of them communicate using SPI protocol. The Arduino is 3 meters far away from the Rfid Mfrc522 module and I used 7 separate cables to connect it and with this setup, it is not working and Arduino it is not able to communicate with the module. Thanks to the Arduino Stack Exchange forum I was able to lower the frequency but this did not work either. Also, they told me to use a CAT5 shielded cable but I have some doubts about the connections. I will include a picture of my schematic below. My questions are:

  • The shielded CAT5 cable is formed by twisted pairs of wires shielded. Which cables on the SPI protocol should be shielded between each other and which one can be "twisted" together? (Although there is a similar question, the answer to this particular question is not specified therefore I still do not understand what SPI pins I can put together and what SPI pins I need to separate.)

Thanks for the help

Conncetions and SPI pins with Arduino

Enzo
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  • SPI ain't good for such "long" distances, especially if speed > 1 MHz. Try RS-4XX. – Mitu Raj Dec 13 '21 at 12:48
  • twisted pairs are intended to compensate a positive against its negative. in other words if sck's voltage vs ground is what matters, you can twist to gnd. expect several gnd cables or plan to build a rather carefully integrated custom ribbon. don't forget that you should not twist power cables as that can generate a signal related to power consumption, which is not a signal you would wish to carry. – Abel Dec 13 '21 at 22:03
  • also verify that it works with a short cable... you can also just try to proportionally increase cross sectional area to keep the resistance the same. – Abel Dec 13 '21 at 22:05

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