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The RDM630 library enables the Arduino to easily read EM4100-compatible RFID-tags using the RDM630 RFID reader module.

Needed hardware for this demo

  • Arduino compatible board
  • RDM630 RFID reader
  • EM4100 compatible tag

How to connect

  • Connect 5V & GND of the module to the corresponding pins of the Arduino
  • Connect the TX pin of the module to pin 6 of the Arduino.
    • You could use another pin of the Arduino, but then you'll have to change the initialisation of the rfid object in the demo code below.
    • If you're using a 3V3 Arduino, you'll have to use extra level shifting. A pull-up resistor between the 3V3 and the Arduino-pin, together with a diode between the Arduino-pin (anode) and the RDM630-TX pin (cathode) will do the trick.

How to program

The library can be downloaded from here.

  • Create a folder named "RDM630" (without the parentheses) in your Arduino-libraries folder.
  • Copy rdm630.h & rdm630.cpp to that folder.
  • Create a new Arduino-sketch
  • Import the "RDM630"-library into your sketch.
  • Copy/paste the following demo application to your sketch
  • Upload & run

#include "rdm630.h"

rdm630 rfid(6, 0);  //TX-pin of RDM630 connected to Arduino pin 6

void setup()
    Serial.begin(9600);  // start serial to PC

void loop()
    byte data[6];
    byte length;

        Serial.println("Data valid");
        for(int i=0;i<length;i++){
            Serial.print(" ");
        //concatenate the bytes in the data array to one long which can be 
        //rendered as a decimal number
        unsigned long result = 
          ((unsigned long int)data[1]<<24) + 
          ((unsigned long int)data[2]<<16) + 
          ((unsigned long int)data[3]<<8) + 
        Serial.print("decimal CardID: ");

The first output is actually the CardID encoded in hex. So e.g. for a CardID (printed on the card) of 0007616525, you will get the following output: 2 0 74 38 D 0

  • The leading 2 is the STX symbol (0x2) denoting the beginning of an ID.
  • The three leading 0s are reduced to one single 0
  • 7438D is the decimal number 7616525 encoded in hex
  • the trailing 0 is proof that the checksum that was transmitted by the module matches the XOR operation performed by the RDM630 library on the received data.

The second output is the CardID as a decimal number (as printed on the card).