RFID reader with basic components not working

Thread Starter

testuserabcdef

Joined Jul 12, 2016
127
circuit.png

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.
 

ian field

Joined Oct 27, 2012
6,536
View attachment 122197

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.
If you're trying to false-trigger supermarket door scanners; you'd be better off with a Franklin oscillator.
 

ian field

Joined Oct 27, 2012
6,536
I'm trying to read data from TK4100 cards
If RFID is anything like door entry keyfobs; there's 2 coils and 2 frequencies.

A large coil for wireless energy transfer at something like the frequency mentioned.

A VHF/UHF coil for the data stream. 433MHz is a commonly used frequency for this kind of device, I believe there's another band at about twice that frequency.

A single low frequency gave the impression of a different purpose.
 

ian field

Joined Oct 27, 2012
6,536
I'm trying to read data from TK4100 cards
If RFID is anything like door entry keyfobs; there's 2 coils and 2 frequencies.

A large coil for wireless energy transfer at something like the frequency mentioned.

A VHF/UHF coil for the data stream. 433MHz is a commonly used frequency for this kind of device, I believe there's another band at about twice that frequency.

A single low frequency gave the impression of a different purpose.
 

BR-549

Joined Sep 22, 2013
4,928
I've never played with RFID. Most seem to want to increase the range. I would think the weak part is the low output of the tag.
Why not try different coil diameters hung on the wall. See if increasing coil diameters......with tag inside coil.....can still pick up the tag signal. If so......why not coil the entire wall/room?
 
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