I have an Raspberry Pi model B, and I want to hook up this RFID/NFC reader I got. This is the one I have.

It has TX, RX, VCC, and GND. When I try to hook up TXD -> RXD and RXD -> TXD (or TXD -> TXD doesn't matter), I cannot get it to respond to anything I do. I have tried 5v and 3.3v, but I prefer UART as it seems more documented, so I go with 5v.

To test if the ports even work, I hooked up RXD to TXD on the Raspberry Pi to create a loopback. Using minicom -b 9600 -o -D /dev/ttyAMA0 to read from the port, I could see my keystrokes. Perfect. But, when I connect my device and I do the same command, I see nothing when I try to read the cards I have, even though the LED blinks when it reads a card.

This should work, but it does not. I did try hooking up the RFID device to my Arduino, then load a library, and I could read the cards through the serial monitor easily. And yes, I did try switching around TXD and RXD. I also tried using screen 9600 /dev/ttyAMA0 but unfortunately that didn't work either.

Anyone out there who can help? Thanks!

  • I hope the output from the reader is 3.3V. Any higher and you will eventually kill the gpio. Also, connect the Pi ground to the RFID ground.
    – joan
    May 26 '15 at 15:16
  • Does the reader output any voltage? It shouldn't. The reader should receive voltage to power it on. Also, it works with 3.3v and 5v, so it shouldn't be a problem (5v for UART / 3.3v for SPI). May 26 '15 at 15:20
  • The TXD to RXD connection is a wire. Just like any other wire. If you put a meter on the wire you can measure that voltage relative to the ground wire. I'd try that.
    – joan
    May 26 '15 at 15:24
  • Unfortunately I don't have a voltmeter, so I can't measure that. But I'm sure it's fine. May 26 '15 at 15:27
  • It's your Pi. It will be fine as long as the voltage is no less than 0V and no greater than 3.3V. Anything outside those limits will eventually damage a Pi gpio.
    – joan
    May 26 '15 at 15:31

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