Archives for category: Example Hardware

First of all I emphasize that unfortunately none the following attempts of reprogramming fused AVRs was successful in my case. Therefore this is more a personal documentation of what did not work, rather than a tutorial on how to get AVRs reprogrammed.

The general problem is, that once the fuse bits of an AVR are set to except an external clock source, the AVRs can in theory only be reprogrammed when they have that external clock source during the reprogramming process as well. In practice it is much more complicated.

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Nearly all search results for RFID on Hack A Day are really interessting examples of what is currently possible with this technology. For example there is the open source passive RFID tag cloner and the configurable RFID tag. The last one (here on its official homepage) is a really close example of what I want to archieve with my AVRFIDs.

Two more online shops with useful RFID sketching materials:

Once more I have a handfull of links, which I haven’t summed up here. First of all I found a really nice tutorial by the Teaching Enhancement via Small-Scale Affordable Labs (TESSAL) Center, introducing into experiments with 13.56 MHz RFID. Their summery of the fundamental concepts is really helpfull in my opinion. Further they provide an short online test, proofing your basic knowledge on RFID, as well as all their materials on this class.

One more short introduction into the RFID basics by Priority 1 Design.

Another RFID introduction mainly from the EPCglobal perspective.

Further more the articles by Roy Want should not be missing.

Stumbled over an really nice and compact 125kHz RFID Module for Arduino. Another one, the RedBee RFID reader with wireless connectivity. And last but not least, an USB Stick RFID reader module.

Using AVRs as RFID chips makes it necessary for me to build a new RFID reader, because this system only operates in the 125kHz frequency (I think this comes from the internal clock of the ATtiny85 microcontroller, but I still have to confirm that). Therefore I have two new RFID modules. The first and older one is the RDM 630 also sometimes refered to its Model Nr. RFR101A1M by SeeedStudio. The second one is a relative new RFID module, the SM125 by SonMicro, with which only little experiments are found in the web. But there is some exsample code and schemes on their support page and a Arduino Library for it in a Github repository.

For the RDM630 exist some example tutorials (1, 2), which help wiring up this RFID module. With the help of the datasheet I transfered this wiring onto the SM125 RFID module. In order to test both RFID modules, I took a big breadboard and integrated both on it:


Here are the pinouts for the RDM630:


And here the pinouts for the SM125 like its in the datasheet:


Here is the Arduino code I used to test the 125kHz RFID modules so far:
#include <SoftwareSerial.h>
#define rxPin 6
#define txPin 7

unsigned char card[12];
unsigned char p;
int printed = 0;
int val = 0;
int bytesread = 0;

//create a Serial object RFID
SoftwareSerial RFID= SoftwareSerial(rxPin, txPin);

void setup()
Serial.println("Serial Ready");
Serial.println("RFID Ready");
pinMode(rxPin, INPUT);
pinMode(txPin, OUTPUT);
Serial.println("P ="+p);

void loop()
if (RFID.available()>0)
//    Serial.println("RFID is available");
p =;

if (p == 2)
//      Serial.println("There is a 2 discovered in the data");
while (p != 3)
//        Serial.println("Reading data");
p =;
Serial.println(", ");
printed = 1;
//    Serial.println("Read completed! ID is: "+p);

if (printed)

//    Serial.println("\n——————");
printed = 0;

Until now both modules are working in that way, that any time a RFID tag comes near, informations can be read. Unfortuntely the data has a wild format and makes no sense yet. I still have to check the wiring one more time, but it also can be a matter of the two formats: TTL and Wiegand. General informations on the Wiegand interface. Further I found some Wiegand specific code, which will maybe help me and a YT-Video explaining the Wiegand format:

I have to dive deep into that probably! I will post some more updates on how I hopefully solved this problem.

In order to get my RFID reader module wired and running, these related works helped a lot:

Example Paper RFID Tag

A RFID tag, build by my supervisor with coper tape and preprogrammed RFID tag chip. With a working frequency of 13,56 MHz.