Payment card conversion questions

I dissolved my regular bank card today and found this inside (https://photos.app.goo.gl/mfrC9yadEeAts6g18)
I was wondering if I could get this (a new one) converted to an implant instead of the westpac paywear? it at least works with my phone’s NFC (will try it at a shop tomorrow) and is smaller and more convenient (I would have to switch banks to use the westpac one)
I know the payment conversion page says

we have not yet been successful converting a “dual interface” card – i.e. a payment card with contact chip AND contactless payment

but I thought I’d ask, it seems different to other RFID cards I’ve talked apart

May or may not have been a discussion about these types of cards (called coil on module or CoM) in the unofficial discord server since yesterday or the day before :rofl:. From what I know, currently they cannot be converted unless you get sufficient range with just the module (as in there are no antennas which are currently designed to couple with the module). That said, it might be possible to create a flex antenna resonant tank that give the module greater range like the rest of your card does.

Note that I’m not part of DT, just simply a member who likes following payment conversion possibilities :sweat_smile:. @Satur9 or Amal would be the best people to give you an official stance.

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Is range the only issue? If so I’ll have a play around and see what I can do
Thanks :relaxed:

Can you scan it with your phone still? It might be hard to do, but if it does still scan, range is likely to be the one of the only issues. One other potential issue that I’m unsure about is whether it will ever ask you to insert it… obviously wearables don’t have contacts, but I’m not sure whether you can just use it contactlessly forever.

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I’m currently exploring a method to convert CoM bank cards. The trouble is that the little antenna circuit on the module is not tuned to 13.56MHz at all, because it’s designed to have mutual inductance with the main coil in the card body. They also are very tiny coils and they have large metal contacts behind which block the field from that side.

IMG_20210705_114614~2

2021-07-01-18-08-07-648

The nice part is that they’re cheaper to produce, so they’re becoming more ubiquitous, and they’re flip-chip WLCSP so they don’t have delicate gold bonds in resin to worry about.

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I wonder what the other foil antenna type structures are, I know some nfc tags have tamper sense :thinking: maybe they won’t work after removal from the card :thinking:

What do you mean? There’s an antenna and some traces that lead to the contacts. It’s for a card designed like this:

CoM_for_GovID.jpg_951475058

Looking at the images @non-bin shared, all the additional foil elements. I get how the packages work I was concerned that they where breaking out something else from the chip.

Ahh yeah, I’ve seen those before in FeliCa cards. Not sure what they’re for. You could be right about the tamper resistance. Could it be a component of the magstripe?

Hmm maybe but isn’t that usually just a surface layer (I assume it’s been eaten away) I suppose we won’t know until we try right :sweat_smile:

Can you scan it with your phone still?

Yes I can, no problem. I’ll try it at an EFTPOS machine today

they have large metal contacts behind which block the field from that side.

I wonder if we could sand that away to get better range? If it works to pay I’ll try that and report back

My main question is @amal, is there anything that would make bio-coating it more difficult?

It worked! The range isn’t great, is the proxmark3 hf tune a good benchmark for range testing?

Not really for COMs … the major problem I have with dual interface chips in most cards is that the antenna seems to be connected through a very fragile wirebond and then drowned in epoxy… so affixing a new antenna to that is basically impossible… and nobody wants to implant an entire credit card sized device (do they?) … so yeah a COM, if it actually works with payment terminals, might be ok to encapsulate.

ok, I just tried comparing the paywear card to the CoM chip, and there’s no competition (paywear works at 2cm, CoM works sometimes but has to be touching the phone). are there any good resources on creating your own antennas though? I’ve already trashed my card so I might as well put it to research use for the community

I also can’t get my proxmark to find the CoM chip, but the paywear one works fine

umm… @amal? I soldered a coil I got from another card onto the chip and it works just as well as the paywear.

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Just some thoughts about it:

My experience is, that’s scanning a payment card in dissolved or with a (diy) air-coil antenna is not representing the comparable environment to a POS terminal and a very bad idea.

In example: I dissolved a german vimpay card, rebuild the antenna 1:1, tested the connection only with my smartphone, everything was fine.
So i covered the diy antenna with the chip with some biosilicone, got it implanted, and guess what - it worked really bad.
So i had to unimplant it.

Why it was not working as tested?
Well, ​it’s about the pF, about meassuring Henry, calculating coils, ferrite foils, interferences of substances like silicone, plastic, size and form of the remote device, skin etc etc.

Even a metall bracelet or a metall watch near the implant can interfere with the connection in good and in bad.

These things and many more things, as allready discussed here, are relevant to the funcinality and the connectivity of the circuit.

My personal result is that I do respect more than ever the effort, the experiences Amal makes to develop a payment solution, and the knowledge he’s got to succeed.
Meanwhile i still experiment with wire, chips, Lcr Meters and myself :slight_smile:

So, let’s keep discovering and developing dangerous things all together

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If you want I can walk you through the calculations for an antenna design. Like Jesse said though, it’s more than just the raw capacitance and inductance values that make a good antenna.

Here’s a video I made describing how to use a vector network analyzer (NanoVNA) that you can get for ~$50 online. You can test antenna tuning with this and see the actual resonant peak, to determine how far off you are from the target (13.56MHz)

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For me is this the most confident way to test the antenna to.
The NanoVna is great I’ve got the same. :+1:

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I’ll look into getting a VNA. I bought some stuff with it this morning, and the scan I got was about 1cm away so I think that’s pretty good, @amal of I sent this (or a new one without the paper) to you could you coat it?

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I know they break, but I really want to put this in my hand.



Got a bunch of red NFC nails and swapped the LEDs for some other colours