I'm trying to make myself a decent RFID card reader with more discrete parts because I want to learn the operation of one.
I have used some ideas from http://www.serasidis.gr/circuits/RFID_reader/125kHz_RFID_reader.htm but I want to make my coil big.
If I fiddle around with the part values enough, I could get this reader to work, but what I don't understand is the math behind the part values connected to the crystal.
When I was testing things out, I noticed that if I touched a component near the crystal or even the crystal itself, then the frequency changes like crazy. I also noticed that if I changed the 4.7M resistor to a different value then the frequency is different. When I changed 100K to 22K, no oscillations occurred (the circuit failed).
What I'm trying to do with the crystal arrangement and the 4060 IC is generate a smooth 125khz pulse to feed into the inductor and the rest of the circuit.
If I were to use a 10mH inductor, could I still get this circuit to work? and I use an LM386 opamp with a 4.7uF capacitor as the compensation capacitor (connected to pins 1 and 8) for high gain.
The cards I'm using ate TK4100/EM4100 compatible.