Grove - 125KHz RFID Reader

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Grove - 125KHz RFID Reader.jpg

This Grove-125KHz RFID Reader is a module used to read uem4100 RFID card information with two output formats: Uart and Wiegand. It has a sensitivity with maximum 7cm sensing distance. There is also the electronic brick version of this module. It can help you with project like internet of thing and access control system.

And you should use these module below while using RFID reader:

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  • Voltage: 4.75-5.25V
  • Working Frequency: 125 KHz
  • Sensing Distance(Max): 70mm
  • TTL Output: 9600 baudrate, 8 data bits, 1 stop bit, and no verify bit
  • Wiegand Output: 26 bits Wiegand format, 1 even verify bit, 24 data bits, and 1 odd verify bit


Here we show how to read RFID information using the Grove - 125KHz RFID Reader. Connect Grove - 125KHz RFID Reader to UART of Grove - Base Shield.
RFID reader.jpg

Uart Mode (Jumper set to the left two pins)

You would need to select the jumper to "U" to enter this mode, and the setting is: 9600bps, N, 8, 1, TTL output

// link between the computer and the SoftSerial Shield
//at 9600 bps 8-N-1
//Computer is connected to Hardware UART
//SoftSerial Shield is connected to the Software UART:D2&D3
#include <SoftwareSerial.h>
SoftwareSerial SoftSerial(2, 3);
unsigned char buffer[64]; // buffer array for data receive over serial port
int count=0;     // counter for buffer array
void setup()
    SoftSerial.begin(9600);               // the SoftSerial baud rate
    Serial.begin(9600);             // the Serial port of Arduino baud rate.
void loop()
    if (SoftSerial.available())              // if date is coming from software serial port ==> data is coming from SoftSerial shield
        while(SoftSerial.available())          // reading data into char array
            buffer[count++];     // writing data into array
            if(count == 64)break;
        Serial.write(buffer,count);            // if no data transmission ends, write buffer to hardware serial port
        clearBufferArray();              // call clearBufferArray function to clear the stored data from the array
        count = 0;                       // set counter of while loop to zero
    if (Serial.available())            // if data is available on hardware serial port ==> data is coming from PC or notebook
    SoftSerial.write(;       // write it to the SoftSerial shield
void clearBufferArray()              // function to clear buffer array
    for (int i=0; i<count;i++)
    }                  // clear all index of array with command NULL

Open the Serial Monitor, the card information can be display as show below:

Read Data .jpg

Wiegand Mode (Jumper Set to the Right two Pins)

You would need to select the jumper to "W" to enter this mode.
The Wiegand demo code for Seeeduino is designed to read Wiegand data in interrupt mode.

In Wiegand Mode, output data is formatted with 26bits including 24bits card info and 2 bits parity.

bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
- PE D P0
- - E 0 -
- - D2[7..0] D1[7..0] D0[7..0] -
  • PE is even bit, PO is odd bit;
  • E is the data bit which was involved in even, O is the data bit which was involved in odd;
  • DX[7..0] is the data bit which correspond to Mifare@ Standard & Light card read only ID;

How to convert the output to Card Number

Take ID: 0009776930 for example:

  • Card Number ID: 0009776930 ------- Decimalism [Start Bit(00) + Card Number(8 numbers)]
  • Output: 0700952F229F ------------- Hex [[Start Bit(07h) + Card Number(8 numbers) + Check SUM]
  • The calculator for decimal and hex numbers is available online.


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