jewelry, rfid, tutorials

one ring to ride them all

Learn how to take apart an RFID-based transit card and embed it in resin jewelry!

I’m 100% the person who is holding up the exit gates out of the subway because I can’t remember which pocket or which part of my purse I put my transit card in. Or, at least I used to be, until I took apart my transit card and put all of the important parts into a ring. Now, I never forget where my ring is (on my hand, duh) and swipe in and out of subway fare gates with ease!

Please note: before attempting this tutorial, it’s worth mentioning that every transit system has different rules for tampering with your card. The BART transit system in the SF Bay Area, where I live, has stated they will accept modified cards as long as they are still fully readable. (SF Bay Area’s MUNI and Caltrain have not commented on whether they will accept the transit ring). But other areas frown on any card modifications and will respond with fines. Just double check to be safe!


supplies needed for this tutorial

transit card(s)

can buy or find around the house: jar, pure acetone, tweezers, packing tape

can get from craft stores: silicone mold, AB resin, decorations

for testing: NFC (Near Field Communication) reader or Android phone with FareBot App installed

1. Brainstorm to design your jewelry

Think about function as well as aesthetic. You could make earrings, but keep in mind that you’d need to remove them to tap in. You could make a necklace, but it would have to be long enough that the pendant can reach the scanner. You could browse Etsy for resin molds for inspiration. I decided to make a resin ring that looks like a chunky plastic ring from the 90s, and found a mold on Etsy with my correct ring size. I chose a ring design with enough space for all of the components inside the transit card, a small RFID (Radio Frequency IDentification) chip and a copper wire antenna.

2. Test transit card

As you modify your transit card, you’ll want to check at every step that it’s still readable by an NFC reader like this one. If you have an Android phone, it probably has an NFC reader built in. To give yourself extra peace of mind, you can check make sure that your transit card’s RFID has all of its data intact by installing the FareBot app on an Android phone. FareBot uses the NFC reader on the phone & can read many different kinds of RFID based transit cards. It can display your card number, your balance, and the last place you tapped on and off.

It’s a good idea to test that your card is readable before you’ve done anything to the card, to make sure your testing systems are working. So, go ahead and check your card before you try any of the other steps!

3. Soaking the transit card in acetone

clipper card in jar of acetone
plastic peeling after 12 hours

Most transit cards are plastic, so they can be dissolved with acetone, the main ingredient of most nail polish remover. Pure acetone works best—the kind in your bathroom closet likely has additional ingredients, but it will also work in a pinch. Acetone has toxic fumes so I recommend working in a well ventilated room.

I’ve tried a couple different workflows, but my favorite one so far is this: putting a transit card in a small pickling jar, filling it with acetone, and closing the lid. The lid keeps the acetone from evaporating and needing to be topped up. Plus, if the acetone isn’t evaporating, it isn’t letting out toxic fumes into the air.

I recommend leaving the transit card like this for 3-4 days. I’ve heard some people say that it only takes 1 hour or 1 day to get the internal parts out of the card, but the wires are really delicate so I like the plastic to be super soft when I try to take the wires out.

Since this is the longest step of the process, and it might take a couple tries to get a ring that both works and is how you want it to look, you might want to set up a few jars to dissolve a few cards.

4. Taking out the RFID and antenna

plastic transit card in acetate peeling after 3-4 days

By 3-4 days, the card plastic should be soft and falling off in layers, so you should be able to take out the RFID chip and antenna (copper wire). The copper wire is quite delicate so be careful and gentle.

antenna & rfid chip separated from the transit card

The RFID chip is what stores your data—your fare balance, when you tagged on and off, etc. The antenna is an inductor that lets a scanner read the data on the chip. These are the two parts necessary for tapping on to the transit system. It’s worth testing the bare card guts to make sure that they’re still readable at this point. (I recommend doing this after every change/step, since if the RFID/antenna ever stops working at any point in time, and you’ve tested after every step, you’ll know exactly what step broke it.

checking that bare antenna is readable by transit app

5. Make the antenna take up less space

For the antenna to work, it has to be in a continuous loop parallel to what is reading it. But we can (carefully) coil the copper wire around a few more times to make a smaller loop so that we can fit the chip and antenna into jewelry. Make sure that the wire stays attached to the chip, and does not break anywhere while you’re doing this. If it does, you might have to solder the wire back together.

Test that this size and shape of antenna fits into the jewelry mold, and also test that the antenna and RFID still work. It also might be worth testing the distance range that the RFID is readable at, since it might have changed from making the antenna smaller. You can do this by holding the antenna at various distances from the reader and noticing what is the maximum distance that the reader can still read the antenna.

checking that smaller antenna fits in the jewelry mold
checking that smaller antenna is readable by transit app

6. Protecc

The copper wires are delicate, as we mentioned, as is their connection to the RFID chip, so once you’re happy with the size, shape, and readability, they might be worth protecting. One of the simplest ways to do this, suggested by my friend Samantha Gold, is to cover the the coil and RFID with clear packing tape, like this:

coil and RFID in clear packing tape
tape trimmed to smaller size to fit in jewelry

Test the antenna and RFID again after this step just to be sure!

7. Putting the RFID and coil into jewelry

Putting the rfid chip, antenna, and resin into your jewelry mold.

Mix the resin according to the instructions on the bottles. Most AB resin has you mix equal quantities of resin and hardener and stir for 3-5 minutes. The hardener causes an exothermic reaction that heats up the resin and makes it hard. You can also add resin dyes to add some color.

Pour the resin into the mold, and insert the rfid and antenna into the resin using tweezers. You’ll want the antenna loop to be parallel to the surface that will touch the reader. So in the case of the ring mold above, you’d want the antenna to be flush against the top of the ring. You can nudge it with tweezers to get it into the right position. You can also add small decorations like glitter or tiny flower petals. If the resin has a lot of bubbles in it, it can help to hold a hairdryer 8 inches above the resin to make the bubbles rise to the surface and pop.

8. Waiting for the resin to harden

Now for what I find to be the hardest part of this process (if you’re using AB resin): waiting 24 hours for the resin to harden. As tempting as it might be to check on the hardening progress by pulling the jewelry out of the mold, that can ruin the jewelry. So just try to be patient!

There is UV resin that cures within minutes using a UV light, but I haven’t had much success with it. So after many failed attempts, I decided to stick to AB resin. Let me know if you have success using this tutorial with UV resin!

9. Take your jewelry out of the mold

What the ring looks like out of the mold. This ring uses flower petals and clear resin.

After you’ve waited 24 hours, it’s now time for the moment of truth! After popping your RFID jewelry out of its mold, try testing it with an NFC reader.

checking if transit app can read ring
checking if NFC reader can read clipper card and ring

9.5 Debugging, if necessary

It can be a huge bummer if, after all this waiting, the ring doesn’t work. But don’t get discouraged! It took me 2 attempts to get a ring that worked, and 4 attempts to get a ring I was happy with. Here are some debugging ideas:

  • Look closely at the wires, have the detached from the RFID chip?
  • Is the antenna parallel when you’re bringing it close to the reader?

Even if you don’t see anything wrong with the antenna or RFID chip, they’re all so delicate when out of their protective encasement that it might be worth just trying the process again and seeing if it works that time!

If you can’t figure out what’s wrong, you could try posting your issue, along with photos, on a forum or on twitter for suggestions! Or just try again. Once you get your project working, be sure to post your solution to pay the help forward and help someone in the future debug!

10. Ride in Style

Now you’re ready to ride public transit in style! Here’s a video of me demonstrating for the local news that the ring works to enter a BART turnstile.

(Note: it’s possible for your rfid jewelry to be readable by your NFC reader but not readable by the transit turnstile, since they might have different sensitivities. So, the first time you take it out for a test spin, bring a long a regular transit card as backup, and if your jewelry won’t scan, you might have to go back to step 9.5)

11. Endless Possibilities

You can make so many different kinds of rings, depending on your taste. Here are a few different ring variations I’ve made:

You can add various dyes to your resin.
This ring used pink dye as well as holographic foil.
This is how the ring looked after the resin set.
The holographic foil helps mask the antenna and rfid chip.

You can add more drops of dye for a stronger color, but beware that too much dye can keep the resin from curing properly since it affects the liquid ratios of the AB resin.

There are lots of creative possibilities! I’d love to see what you make if you try this tutorial!

Thanks to this tutorial for a guide on how to dissolve a clipper card and to Samantha Goldstein for debugging advice! And my brother for the title inspiration.