Compressing an Opal card

Please note, idk if this is still a “legally valid opal card” when if it works transits might be old fashioned, in a bad mood or butthurt that your opal card is cooler than theirs! (or perhaps there’s a ‘do not tamper with card’ rule?)

Hi all,


A few years before Sydney had an electronic ticketing system, I read an article where a man in London performed some experiments on his Oyster card, and turned it into a ring! ( )

Inspired by this I set out to do something similar with my Opal card.

I found an old  Opal card I had laying around, scanning it reveals I had $1.17 left on it, I can sacrifice that if the experiment fails.

So I took a deep plate and put about 25ml of acetone into it, then I submerged the Opal card.

Around 30 minutes later I returned to check on it and great! it was dissolving! all the outer layer had gone funky, pics after the break!

I removed the funky stuff and then set the card back into the bath upside down to get the other side, again 20 minutes later it had the same effect. the sides of the card had been peeling up so it was kinda difficult getting it evenly dissolved.

I managed, and after a while I had a thin card with the antenna and chip in it.

The chip was inside a cutout in the card, probably to reduce size, The antenna removed itself from the chip so maybe it was just pressure fit?

Either way with some careful finger work I was able to strip the antenna out of the card as I couldn’t get this piece to dissolve.

With the antenna and chip free, I re attached the antenna to the chip with some solder  (enameled wire antenna, I accidentally burnt about  8mm of the wire off when removing the enamel, but it still functions fine.)


After it was back together, I scanned it with my phone and hurray! it still scans!

So I folded the coil in on itself creating a coil half the size, and tried again to scan it. IT WORKED!


I folded it once more to make it around the size of a 10c coin, and then tried once more and OMG it still works!

To finish it off for now, I took a small thick plastic bag, and inserted the coil, pushing it neatly into the corner. I cut the plastic bag as close to the coil as I could to get minimum size, and then put some kapton tape over the two open sides.

I now have a small rigid opal card.

I had a Visa paywave band that I got from my mobile telco, Optus. Its just a silicone wrist band, and a small Visa paywave card. maybe 20x30mm ?

I ordered a second one, in red, because I can do so for free.

When it arrived, I inserted my new small opal card into the wristband and put it on my wrist.

To my amazement through all that silicone and plastic the card could still easily be scanned by my phone!

Even with the reduced coil surface area!



I have yet to test it in production, I will do so this afternoon. I will load it with $5-10 and see how it goes.


For now, enjoy a few random photos I took during the process:


Opal Card dissolving


Optus Visa PayWave band + finished miniOpal:

miniOpal and Cash by Optus band





I did some testing, the new style opal loading machine keeps saying invalid card, the old style one gives me the option to top up and correctly reads the balance, however it sometime scans saying “multiple cards detected ”
The gates take a bit longer to read the card than a normal full size card, and they take a few times to find the right spot, note: this is more difficult when its in the wrist band and on the wrist!


I think it’s not worth the extra time to have this form factor



DJ Sona Audio and Light prop

Im going to be working on a DJ Sona (LOL skin) cosplay prop for a friend, Ill stick info into this post.


That should just about cover everything.

mash it all up together and let someone else make the details

maybe lasercut the perspex to shape ? is there enough to make the spinny things also ?