How to make a FSK Rfid Tag that works at 125 kHz?

Projects General Guidance
1

I am trying for some time to make my own rfid reader following the ideas on the DIY FSK RFID Reader.
My primary problem now is that i do not have a specific rfid tag to test the reader so i decided to make my own using also an arduino uno. The only information on the internet which i found is at FSK Modulated Signal. I really need to know how to write the code to transmit the id from the tag to the reader.
I mention again that the tag needs to work at a 125 kHz frequency and needs to use FSK modulation.

2

To transmit data from an RFID tag to a reader, simply switch a 1K resistor across the coil to get high and low signals.
Detuning will ensure that you have both FSK and amplitude modulation.

3

And the code needs to suffer some modifications? To make the manchester codification a figured out it will sound like this:

int output = 9;

void setup()
{
  pinMode(output, OUTPUT);
  digitalWrite(output, LOW);
}

void loop()
{
  int code;
  int data[64] = {1,1,1,1,1,1,1,1,1, 1,1,1,1,0 ,1,1,1,1,0, 1,1,1,1,0 ,1,1,1,1,0, 1,1,1,1,0,
                       1,1,1,1,0, 1,1,1,1,0 ,1,1,1,1,0, 1,1,1,1,0 ,1,1,1,1,0, 0,0,0,0,0};
  
  for(int i = 0; i < 64; i++)
  {
    code = 1 ^ data[i];
    if(code == 1)
        digitalWrite(output, LOW);
    else
         digitalWrite(output, HIGH);  
    delayMicroseconds(256);

    code = 0 ^ data[i];
    if(code == 1)
        digitalWrite(output, LOW);
    else
         digitalWrite(output, HIGH);       
    delayMicroseconds(256); 
  }
}

After some tests the reader seems to not recognize the tag. It is also possible to be some mistakes at the prototype of the reader (at the quality of the parts). When you said to use 1k resistor did you actually mean something like this:

4

When you said to use 1k resistor did you actually mean something like this:

No. I said:-

switch a 1K resistor across the coil

Across means in parallel. That circuit does not switch anything, it simply has a 1K resistor in series PERMANENTLY with the coil.

There is no need to use Manchester encoding either although you can if you want.