I did some research on different inexpensive RFID readers and I ended up building my project around this one


I also bought these tags:


The problem is that whenever I get close with the tags, sometimes it doesn't read them at all, other times it takes 1-10 seconds to read it.

I use this code to test it on my ubuntu (I tested it on a raspberry pi as well, same issue): http://theatticlight.net/posts/Using-a-Parallax-RFID-reader-on-the-Raspberry-PI/

I am not sure if this is a problem with my reader or something else I am doing wrong.

Would a 13MHz reader/tag have faster reading speeds? Is this problem related to the specific antenna of the module?


1 Answer 1


I built a custom RFID card reader for the exact same protocol you are using and was able to read cards every time in just a few hundred milliseconds tops...

My reader included an Atmega328p connected to LC tank (large wire wound coil for L to act as antenna).. The LC tank was then reconnected to a pin of the Atmega through a 2 stage filter and then a schmitt trigger.

I would say its a problem with the reader or something you are doing for sure... 125kHz tags are not that slow. Should be MUCH faster (as I stated, just a few hundred milliseconds tops, I never logged exact timing... but it appeared instantaneous to all users)

  • \$\begingroup\$ Ok could it be that the antenna is too weak on this board? \$\endgroup\$
    – iordanis
    Commented Mar 5, 2017 at 19:55
  • \$\begingroup\$ Could be a ton of things... But it's not an inherent problem with the 125kHz EM4100 protocol \$\endgroup\$ Commented Mar 5, 2017 at 19:57
  • \$\begingroup\$ Did you use external antenna or an on-board build in? \$\endgroup\$
    – iordanis
    Commented Mar 5, 2017 at 20:14
  • \$\begingroup\$ The 125k reader I made used a large wire wound external antenna. I have also made a 13.56MHz reader board based around the TRF7970a that I designed a PCB trace antenna for. \$\endgroup\$ Commented Mar 6, 2017 at 0:03
  • \$\begingroup\$ you noticed any difference in reading speed performance between the two solutions? Is 13.56MHz inherently faster at reading? Do you know how big was your wire wound? What distances could you read with it successfully? \$\endgroup\$
    – iordanis
    Commented Mar 6, 2017 at 5:17

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