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PostPosted: 17 Apr 2015 15:13 
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Joined: 19 Sep 2013 11:36
Posts: 17
Hi,

I'm sharing information how to get more rf power from china made rc522 board.
My project uses MFRC522 board and Mifare Ultralight C cards.
This board can not produce enough RF energy to get Ultralight C card up and running
MFRC522 datasheet says that max TX current is 150mA, but measured current was only 7mA.
I have a very good RF design experience so I started to measure whole RF part and make full tuning.
And what I found, antenna is tuned, not perfectly but usable, so was matching cirquit. But used 2.2uH
inductors does not meet with required parameters.
Solution: Replace inductors L1 and L2 with same inductance (2.2uH) but higher operating current.
like this one: http://www.tme.eu/en/details/cw1008-220 ... ferrocore/
Now RC522 can read Ultralight C cards with no problem, also NTAG203 card reading distance is ~70mm


WARNING!!
RC522 RF output pins are very static sensitive!
Without proper equipment you can easly
damage your rc522 reader board!!


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PostPosted: 24 Apr 2015 15:12 
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mikroElektronika team
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Joined: 25 Jan 2008 09:56
Posts: 9282
Hi,

Thank you for sharing this :)

Regards,
Filip.


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PostPosted: 10 Feb 2016 17:43 
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Joined: 10 Feb 2016 17:37
Posts: 1
Hi Ermok

Thank you for your tip on the inductor.

I was having the same problem. By the way, what other values (capacitors) did you find to obtain the correct tuning? I got several boards from ebay/amazon that has different values...

Would you give us the best values for the capacitor pairs (I had 47pF C4/C5, 10pF for C10/C11, 180pF for C8/C9 and 15pF for C6/C7)

Regards,
Sergio P. SIder


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PostPosted: 06 Apr 2016 21:05 
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Joined: 19 Sep 2013 11:36
Posts: 17
Hey,

I made some tests with sweep and figured out that coil has good parameters.
Not perfect in first moment, but checking working bandwidth ~800KHz I found that
resonanze frequenct is correct and not need a fine tuning. But harmonic and matching circuit
needs to be tuned. Lot of work, several tests and after building a completly new
measurement equipment based on 40MHz DDS and 90db logaritmic detector I figured out that
C4 and C5 must be changed. Replace them with 33pf capacitors. And that's it.


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PostPosted: 06 Jan 2017 15:02 
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Joined: 06 Jan 2017 14:57
Posts: 1
Wow, thanks for sharing this information. By the way, does anybody have the board routing file (or gerber) of this board ? I would like to integrate its design in a more complex project and I'm not able to design the antenna and tune capa/resistor by myself :(


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PostPosted: 25 May 2017 17:10 
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Joined: 25 May 2017 17:05
Posts: 1
Thanks for the tip!
After replacing L1 and L2 on my $5 RC522 reader from Amazon, it can now read Ultralight C and Desfire EV1 cards at about 3cm.
Before it was not able to read these cards at all.

FYI for those of you in the USA like me, these are the Inductors that I used:
http://www.mouser.com/search/ProductDetail.aspx?r=710-74479887222C
They fit just fin on the existing pads and look much beefier!


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