Help identifying a NFC reader board that is <=25mm

General project help for Adafruit customers

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
nat1craft
 
Posts: 3
Joined: Wed Oct 23, 2019 2:02 pm

Help identifying a NFC reader board that is <=25mm

Post by nat1craft »

I am looking for help finding a NFC reader board that is physically less than 25mm square. I want to place this into custom game pieces that fit on a board of 25mm (1 inch) squares (one piece occupies one square). I want each piece to independently read either its location (from a tag in the board) or from an external source (tag, card, etc..) The reader will be stacked with other hardware to control it, react to the read, etc. along with a battery. I believe I have the other pieces identified, but require a suitably small (and hopefully widely compatible) NFC reader board. Any ideas on a make/model or a good easy DIY alternative for something this small?

User avatar
adafruit_support_mike
 
Posts: 67446
Joined: Thu Feb 11, 2010 2:51 pm

Re: Help identifying a NFC reader board that is <=25mm

Post by adafruit_support_mike »

For that application, you'd probably be better off using capacitive RFID rather than inductive RFID. The major circuits and signals are pretty much the same, but the antennas and method of power transfer is different.

Inductive coupling works by overlapping the magnetic fields of two current loops. The laws of physics can't isolate 'the magnetic field of loop A' from 'the magnetic field of loop B', so anything that happens in one loop has a measurable effect on the other one. The problem is that the strength of a magnetic field is proportional to the area enclosed by the loop, so making the loops smaller reduces the coupling by the square of the loop diameter.

Capacitive coupling works between two plates that are close to each other. Changing the voltage on a plate involves pushing electrons into or out of it, and the electric field from those electrons extends across a short gap. A high-frequency signal will pass from one plate to another even if there's an air gap between them. And since capacitive coupling works across short distances, you can make the plates smaller as long as you keep the gap between them small.

I'm afraid we don't carry anything that does RFID with capacitive signals though. You'll need to check the major vendors (TI, Microchip) to see what devices they have.

User avatar
nat1craft
 
Posts: 3
Joined: Wed Oct 23, 2019 2:02 pm

Re: Help identifying a NFC reader board that is <=25mm

Post by nat1craft »

Thanks for the great explanation and advice! I will definitely look into possible capacitive RFID (which I didn't know existed). So thank you again.

In the meantime, I realized that it MAY be possible to find an inductive RFID reader <=25mm if... I can find one that separates the antenna from the reader itself. So instead of having the reader + antenna baked into the the same PCB, trying to find just the reader part and making my own antenna to fit the form factor (possibly scavenge one from a tag with the right form factor). I actually came across a potential chip like this in the Mikroe Extend Click Board https://www.mikroe.com/nfc-extend-click and ordered one for experimenting. Its a millimeter or so too large, but it looks like I Might be able to file it down.

Also: I have seen (on the interwebs) inexpensive "buttons" that are meant to be RFID access card readers. They are <= 25mm circular (metal) buttons that are activated by RFID tags to open the lock. The button has a few leads coming out of it to operate the separate access mechanism. This iButton-MF is the form factor I was looking for, however... I believe they are housed in tamperproof cylinders and unknown specs of the chips inside. (need more investigating) They are also listed at 12V, but I wonder if they work at 5V or 3.3V. There are a few variations but something like this: https://www.alibaba.com/product-detail/ ... 76238.html

Side note: I do think a RFID access button like this might make a good Adafruit product! Heck, even the mini antenna-less RFID reader too.

Locked
Please be positive and constructive with your questions and comments.

Return to “General Project help”