Oyster Card RFID Ring Mk3


Oyster Card RFID Ring Mk3

25th of November, 2014

Rfid ring mk3

I've been playing around with RFID Rings for a while now. Using a ring to control access to the hackspace door, as an Oyster card (yeah, I said it - I'm sure TFL don't really care) and generally as a way to interact with things is quite fun and cool. I've made some progress from the last version and significantly improved on it.

rfid ring mk3

The Mark2 was pretty good but suffered from a couple of flaws. 3D printing is not ideal for jewelery placed close to the body. For one thing, stuff can get into it (this is why you never really see 3D printed ear-tunnels) and secondly, they don't really hold up too well. The Mark2 suffered from being a signet ring. The aerial was small but not the smallest and since one had to wear the signet upside down, it looked odd. The cap also came off at one point so it clearly wasn't robust enough.

For the Mark3 I decided I'd use proper jewelery making techniques instead. I'd discovered that the circular RFID aerial can be bent to a point and still work, with a small drop in efficiency. This means the aerial and chip can effectively wrap around a finger. Setting the aerial into resin allows for a more robust and pretty result.

The first thing to do is create a form. As I know all the sizes I decided to 3D print the actual mould. I went through a few sizes before I found one that was comfortable. I proceeded to sand down the result so the layers would not show in the final design. Had I used a different plastic (PLA I think) I could have used acetone to smooth it off. Another use for 3D printing potentially! Just not a popular one! :P

Mould and form

To create the mould, a two part solution is smushed together and the form is set into it. In about 10 minutes, this turns into silicone and we have our mould. It looks a bit messy but it's actually quite neat inside where it counts. From here on in, we can place in our aerial and pour over our resin. All the way through this process I'm testing to see if the aerial is still working, using an old android phone, almost like a heartbeat monitor! :P

The first stage is quite disappointing. Even with sanding the mould picked up even the minute imperfections. The result had a matte plastic look, instead of being pearlized. The answer, it turns out, is to dome the result with more resin. This takes a long time. One has to apply resin and slowly turn the ring for a few hours. This is best done whilst watching a good film!

First Result

The final result looks quite good. It wears well and looks like any other ring. The RFID aerial does work on a particular transport service, so long as the right side of the ring is presented to the reader. To this end, I've put a little mark on it so I know which side to use.

I'm quite glad I came back to this project. It's been quite good fun and the end result is something quite wearable. So good it just blends in to normal life but makes it slightly more awesome. Many thanks to the awesome fearandsequins for teaching me some proper techniques.