Contactless Payment Signet Ring - With Minimal Inductive NFC Antenna - Coil on Chip.

Did you build the previous ring i made an instructable for?

Do you feel that you want to shrink the antenna in size, and maybe use some fancy science to make the antenna hit that sweet spot of 13.56MHz?

Then this guide is for you!

• Follow step 1, 2, 3 and 4 from my previous guide.
• Copper magnet wire, i used the 0.1mm for this build.
• Glue stick, so that the wire and chip stick on the ring.
• A NanoVNA, to optimize the antenna design.
• An NFC antenna for the NanoVNA. There is a guideish on how to build one in step 2.
• An Android phone or tablet with NFC the app Credit card reader - For testing out the chip and ring.

Optional

• A pair of tweezers - They just make life easier!
• The stl file below, so you don't have to make your own!

The main difference from this build is that the antenna is now "around" the chip instead of the whole ring.

I used TinkerCAD for the design and I'm quite happy on how it turned out!

The cut out where the antenna is resting is 1mm deep and 1mm wide.

First of all, a super-quick guide on how to make the antenna, this is actually kind of meta, an instructable inside of an instructable..

Instructableption!

1. Take the SMA male to male connector that came with the NanoVNA.
2. Cut it in half.
3. Remove the black insulation.
4. Make a small hole in the silver mesh and drag out the insulated copper wire.
5. Twist the silver mesh to a wire.
6. Remove 2cm of the insulation around the copper wire.
7. Solder the silver mesh wire to a small alligator clip.
8. Solder the exposed copper wire to a small alligator clip.
9. Make an antenna, I made mine with 1mm copper wire turned around the glue stick 4 times.
10. Connect the alligator clips to the antenna.

Attach it to CH0 of your NanoVNA, turn it on and use the following settings.

1. DISPLAY > TRACE = Only use TRACE0 - To declutter the display.
2. DISPLAY > SCALE > SCALE/DIV = 5 - Basically the resolution, it will be easier to see the frequency.
3. STIMULUS > START = 12M - We will start measuring at 12MHz.
4. STIMULUS > STOP = 15M - We will start measuring at 15MHz.
5. CAL > SAVE = SAVE X - Save it to a number and restore it from "RECALL". Otherwise all settings will be deleted after the next reboot of the NanoVNA.

We are done!

As you can see the antenna is working like a charm!

The contactless payment card is tuned to 13,8-14,0MHz, this is normal since the payment terminal is quite forgiving and accepts frequencies a tad higher or lower than 13,56MHz.

Now, let's tweak the antenna on the ring!

I did the same as with the last ring, glued the chip inside the signet and glued the wire in place with the glue stick. After that I started turning the wire, after about 30 turns i cut the wire and started testing the rings antenna with the NanoVNA. It was on the low side, around 12MHz so i removed half a turn, and tested with the NanoVNA again.

After a a really, really short while the NanoVNA told me that the ring antenna was tuned to 13.5-ish MHz so i glued it in place and tried it on the Android phone, HUGE SUCCESS, it reads the ring from a distance of about 3cm.

It works great "in the wild" and i haven't had any issues on new or old payment terminals.

• What to do if the ring doesn't work in the wild?

The problem might actually be the payment terminal, you tweaked the ring antenna with science FFS, it's solid!

• Can i use a different wire?

Damn right you can, i have used 0.1mm and 0.05mm wire. The 0.1mm wire is more sturdy and won't snap as easy.

• With a spanking new NanoVNA, will you update the previous guide?

Absolutely! It will be updated in the next couple of days!

Lastly, thanks to all of you that asked questions and suggested improvements!

Buy me a coffee? a NanoVNA, a 3D printer so I can make more jewelry with payment options, maybe a clip onfor an ordinary watch or a neckless?