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

wilsonharper.net

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

#13

Post by HawtAds »

adrianwaj wrote: post #9

"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 w…

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.

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

#17

Post by adrianwaj »

HawtAds wrote: post #13
adrianwaj wrote: post #9

"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 w…

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.

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

#18

Post by jacquesm »

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.
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