Rfid-repurpose a 125khz to 134.2khz

Other Hardware General Electronics
1

I have a 125khz rfid reader, pretty simple one, and I have two questions:

  1. can I repurpose the reader to work at 134.2khz?

  2. is there a way to make it work on both frequencies??

Thanks!!

2

Is there a way to use this Arduino Playground - DIYRFIDReader but for 134.2khz?

Theres virtually very little information about this freq.

3

You can modify the circuit shown here http://playground.arduino.cc/Main/DIYRFIDReader to work at 134.2 kHz. The coil will need to have fewer turns so that the combination of L1 and C1 is "resonant" at 134.2 kHz instead of 125 kHz. There are standard formulas for the resonant frequency as a function of the coil inductance (which in turn you can estimate from the size and number of turns) and the capacitance of C1. Google "LC resonant frequency" and "coil inductance formula" to learn more.

4

jremington:
You can modify the circuit shown here Arduino Playground - HomePage to work at 134.2 kHz. The coil will need to have fewer turns so that the combination of L1 and C1 is "resonant" at 134.2 kHz instead of 125 kHz. There are standard formulas for the resonant frequency as a function of the coil inductance (which in turn you can estimate from the size and number of turns) and the capacitance of C1. Google "LC resonant frequency" and "coil inductance formula" to learn more.

Thanks will dig into it now. Regarding that circuit, on the playground l1 (the only) and is it c1 are thr ones determining the resonance. (There are 6 capacitors)

Also, theres a line of code that states changing if using 134: I need to change l, c and the software value?

5

L1 and C1 determine the resonant frequency. You can change either or both, but you will need some way to test whether the final frequency is accurate. An oscilloscope with an accurate signal generator is needed.

From this comment in the code: // the argument value is in microseconds per RF cycle, so 8us will yield RF of 125kHz, 7us --> 143kHz, etc.it appears that you have to choose either 7 or 8 (an integer) and neither is a good match. You can have a timer generate a signal quite close to 134.2 kHz, but you will have to write your own timer initialization code (using a different timer prescaler value).