How to make a FSK Transponder 90/100 KHz

I am trying to make a FSK Transponder that switches between 90 and 100 khz (No return to Zero) but I miss the details to start.

I saw the projects DIY FSK RFID Reader and How to make a FSK Rfid Tag that works at 125 kHz. I also see that Demodulating FSK radio signals uses Softserial to do it but I’m not experienced enough to get going.

Can someone help me going or awnser if it is possible with the arduino?

At first I like to buld a datalogger to understand the data. In a second fase I maybe want to build an transponder to see if i understand the data but first I have to see if my info is correct about how it works.

For more ideas, here is how to make an RFID tag with just an ATtiny85, and a coil.

jremington:
For more ideas, here is how to make an RFID tag with just an ATtiny85, and a coil.

Thanks for the idea but I'm not building an RFID tag. RFID works on an diffrent frequency. That is exactly the problem that I'm facing. To change the frequencies.

Perhaps this patent will help:
https://www.google.com/patents/US5587712
"Transponder having microprocessor generated frequency shift signals"

They specifically mention 90 and 100 kHz.

To change the frequencies.

Given a functioning circuit, changing the frequency of operation is one of the very simplest tasks.