125Khz RFID module - UART


RDM 125KHz card mini-module is designed for reading code from 125KHz card compatible read-only tags and read/write card . It can be applied in office/home security, personal identification, access control, anti-forgery, interactive toy and production control systems etc.
Note: Module will notify whenever 125khz tag approaches, tag serial number will be send via TX pin. Easy way for a RFID module on MCU projects or PC connnection via UartSB.


  • Support external antenna
  • Maximum effective distance up to 50mm
  • Less than 100ms decoding time
  • UART TTL interface
  • Support EM4100 compatible read only or read/write tags
  • Built-in external bi-color LED and buzzer driver
  • Small outline design


May include key specification and other specifications.

Key Specification

Baud Rate9600 (TTL Electricity Level RS232 format)
interfaceWeigang26 Or TTL Electricity Level RS232 format
Power supplyDC 5V(±5%)
Operating range>50mm(Depend on Card/Tag shape, manufacturer)
Expand I/O portN/A
Indication lightN/A
Working temperature-10℃~ +70℃
Storage temperature-20℃~ +80℃
Max. humidityRelative humidity 0 ~ 95%
Size38.5mm ×19mm×9mm

Pin definition and Rating

Look the image below(Mechanic Dimensions), and check the pin definition list here:
 Pin Definition :
   PIN1    TX
   PIN2    RX
   PIN4    GND
   PIN5    +5V(DC)
   PIN1    ANT1
   PIN2    ANT2
   PIN1    LED
   PIN2    +5V(DC)
   PIN3    GND

Mechanic Dimensions


TTL Interface RS232 Data output format

  1. 9600bps,N,8,1
  2. CHECKSUM: card 10byte DATA entire do XOR operation
    0210ASCII Data CharactersChechsum03
Example: card number: 62E3086CED
  • Output data:36H、32H、45H、33H、30H、38H、36H、43H、45H、44H
  • CHECKSUM: (62H) XOR (E3H) XOR (08H) XOR (6CH) XOR (EDH)=08H

Time sequence chart


Output date(HEX): 02 | 30 31 30 30 30 37 33 34 45 30 | 44 32 | 03 ->Change to Decimal CardNumber Decimal: 48 49 48 48 48 55 51 52 69 48 CheckSum Decimal: 68 50 ->Refer to ASCII table,get Ascill value CardNumber Ascill: 0 1 0 0 0 7 3 4 E 0 CheckSum Ascill : D 2 (01H) xor (00H) xor (07H) xor (34H) xor (E0H) = D2H


Connect RX/TX to Arduino UART port , Uart demo code :
void setup()
void loop()


Help us make it better

Thank you for choosing Seeed. A couple of months ago we initiated a project to improve our documentation system. What you are looking at now is the first edition of the new documentation system. Comparing to the old one, here is the progresses that we made:
  • Replaced the old documentation system with a new one that was developed from Mkdocs, a more widely used and cooler tool to develop documentation system.
  • Integrated the documentation system with our official website, now you can go to Bazaar and other section like Forum and Community more conveniently.
  • Reviewed and rewrote documents for hundreds of products for the system’s first edition, and will continue migrate documents from old wiki to the new one.
An easy-to-use instruction is as important as the product itself. We are expecting this new system will improve your experience when using Seeed’s products. However since this is the first edition, there are still many things need to improve, if you have any suggestions or findings, you are most welcome to submit the amended version as our contributor or give us suggestions in the survey below, Please don’t forget to leave your email address so that we can reply.
Happy hacking