Show HN: NFC Energy-Harvesting PCB Business Card with an MCU

Cool project :D

I don't know a lot about this area, but I like the [1 doge = 1 doge] thing where people completely stop thinking about dollars and crypto-to-fiat conversion.

The card can work with Lay-buy/lay-by:

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You go into a store, pick something out. Get a crypto address for it and the amount required with your special card. They set the thing aside. You leave and return to the store when the transaction has gone through and get your stuff.

You don't pay immediately because you don't want to be walking around with a crypto wallet or a crypto debit card. The merchant doesn't want to pay fees either when dealing with an intermediary. There's no fiat conversion either, at least not as a given.

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Gemini says this:

"If you want to do this today, ask the merchant to print or email you a dynamic checkout invoice/QR code so you can complete the transfer on your own device later."

But how widespread is that?

"It is virtually non-existent at retail scale. While the underlying technology exists, you will practically never encounter this specific workflow in the wild."

https://share.gemini.google/ZBHVZo47ZSn1

The "special card" is an evolution of that use-case and organizes it better. You can leave home without thinking about dollars, ready to pay with crypto and not worry about being robbed. No worrying about stockpiling a bunch of receipts either. It's just a 2-step buying process, that's the downside. The shop also has to hope you end up paying once they set it aside. Maybe they'll need a deposit. They can offer deliveries?

Another idea is to pay online and collect it later. Use the card to authenticate yourself when you collect. That would need some decent tech backing it. Make it non-committal where if you don't collect within a certain time frame, you get your money back but lose a penalty chunk.

Isn't this what smart contracts are designed for - crypto transactions tied to real world events? The "special card" provides those events.

[ conversation continued via link above ]

The key feature of this is the zero power storage on the business card.

In a drone or robo delivery case, there is already a massive power storage budget available, so I don’t see the particular advantage of this hack being relevant.

> I should explain how NFC works: Your phone emits a small magnetic field several times a second. An NFC card picks up on that field, making your phone act like a tiny wireless charger. 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.

Can somebody explain how this actually works (Physics + Technology) with pointers to further resources? I have been meaning to look deeper into "Energy Harvesting Systems" and running a MCU using that but never really sat down to research it properly. Some links;

University of Washington - WISP (Wireless Identification and Sensing Platform) - https://sensor.cs.washington.edu/research/wisp_1

Perpetually Powered Energy Harvesting Systems Using the MSP430 MCU - https://www.ti.com/video/3870842958001

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