Look at that subtle off-white coloring, the tasteful thickness of it. Oh my God, it even has a schematic

"The card never actually transmits a message back to your phone. Instead, it changes how much energy it absorbs from the field, and your phone detects those power dips and converts them to binary data. Most NFC tags use this harvested energy only to run their internal circuitry, but some NFC chips are able to take excess DC voltage and route it out to external hardware. This business card uses that last feature."

I wonder if it can be applied to robo-couriers and drone drop-offs. One of those comes to your door, you get your stuff, and you pass something that is powered-up over its sensor and it drives off. It's the equivalent of signing-off on a delivery. The sensor obtains and stores information about you as well.

Maybe I've got it wrong and the recipient needs the sensor and the driver has the powered device that only switches on when it is ready to do the drop off.

With this card, what are the information transfer and storage scenarios? Would be great to see a table. Can the two parties both exchange and store information with minimal power? A card with a little battery and power-on button? Card can have some type of port? Can it be be used as a crypto wallet with a kill switch in the event of a robbery or home invasion?

I think this is important in Hub-and-Spoke communities (previous comment) where population densities decrease but there'll still have to be a lot of exchange going on. Offline-based interactions are a good idea too - keep the airwaves clean.

I think you are overcomplicating things. You have a power envelope, and you have to design your application around it. That's pretty much it. From an engineering perspective, there's no real complexity when it comes to the hardware, software protocols operate one level higher. Your app lives and dies by its power budget.

Yep, good point.

Another interesting use case would be using the card as part of a crypto escrow.

The problems being solved here are:

- walking around with a device that can access a large wallet that could be accessed under duress or coercion

- Key Pairs are hard to remember and type

___

- pre-pay an escrow online with $100

- have a payment card in your pocket

- meet person with another card

- set a payment amount

- touch cards

- escrow unlocks the amount as soon as either card pushes the update online - which if online could be immediately

- card confirms the transaction??

- can also delay the transaction, and if both cards are lost in the meantime, the transaction doesn't go through

- can also specify the payment amount as "set later"

- receiver can also request an amount

- escrow can be funded after the meeting

- good for 1:many payments too, eg splitting a bill

____

cards could also be Key Pair generators, for transferring public keys to other cards, with the exchange recorded for later use. No escrow required. A lot of benefits over handing out printed QR codes of addresses.

For future PCB business card ideas: it would be dope if it can play audios.

Gemini says you can power a piezo buzzer (causing a small bump on a PCB) w/ NFC (just enough power to drive it) to play the modem dialup handshake audio.

What an incredibly neat hack, congratulations. In the 80's Motorola had a challenge-response system to open doors with badges that contained a good bit of circuitry that reminds me of what you've built here. Super impressive. I never realized NFC put out so much energy that you could light a bunch of LEDs with it and power a micro controller this large.

Okay, I really like this, but I found your Easter egg, and it plays to my Ham Radio heart.

I wonder if it could run LoRa chip & MCU long enough to send. MeshCore message. :)

Really cool. I'd love to be able to order cheap ones in packs of 5 or 10, with custom led colors/locations/sizes/brightness, fitting into a printed card...

My wallet has enough NFC devices already trying to talk to each other. Still, a seriously neat piece of engineering!

What do you mean? What's in your wallet that's an NFC transmitter?

cool project, especially as a bachelor student of EE!

Really great project, thanks for sharing and what a well done write-up! Also kudos for including the PCB, BOM, and code on GH with a permissive license.

Nice write up!