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

231 points by WilsonHarper 1mo ago

thenthenthen 1mo ago
Nice write up!
danshagen 1mo ago
cool project, especially as a bachelor student of EE!
- WilsonHarper 1mo ago
  Thank you, I appreciate it!
chews 1mo ago
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.
deleted 1mo ago
[deleted]
badatnames 1mo ago
Look at that subtle off-white coloring, the tasteful thickness of it. Oh my God, it even has a schematic
yegle 1mo ago
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.
- nielsole 1mo ago
  Different idea: https://hackaday.com/2024/06/06/2024-business-card-challenge-tiny-midi-keyboard/ https://hackaday.com/2024/06/06/2024-business-card-challenge...
entrepy123 1mo ago
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...
- WilsonHarper 1mo ago
  I wondered if people would be interested in purchasing them. The challenging part is that they become cheap only when ordering large quantities, and most fab houses consider a different silkscreen to be an entirely different job. I'd have to order, say, 500 blanks, and then print onto them myself. Maybe there's a market for that -- but it's open source, so it's not too hard to make your own :)
adrianwaj 1mo ago
"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.
- HawtAds 1mo ago
  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.
  - adrianwaj 1mo ago
    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.
Sorrel47 1mo ago
My wallet has enough NFC devices already trying to talk to each other. Still, a seriously neat piece of engineering!
- Neywiny 1mo ago
  What do you mean? What's in your wallet that's an NFC transmitter?
basil_io 1mo ago
[dead]
myshapeprotocol 1mo ago
[dead]
ironqcold 1mo ago
[dead]
m4rtink 1mo ago
I wonder if it could run LoRa chip & MCU long enough to send. MeshCore message. :)
jacquesm 1mo ago
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.
- WilsonHarper 1mo ago
  Thanks! Most datasheets seem a bit vague when it comes to listed power output, probably because conditions can vary so much between devices and environments.
k7peak 1mo ago
Okay, I really like this, but I found your Easter egg, and it plays to my Ham Radio heart.
- WilsonHarper 1mo ago
  Thank you! I recently earned my General license :D
cowthulhu 1mo ago
I would be really interested to know the cost per card, both at the single card volume as well as the 30 the author ended up getting.
- officialchicken 1mo ago
  Me too, despite being delightfully surprised by the BOM widget in the article.
  - WilsonHarper 1mo ago
    The total came to roughly $150 for the cards and another $100 for shipping + import fees -- so roughly $8 each. That's more than I hoped, but the ENIG finish, 0.8mm thickness, and higher-quality silkscreen added up. If I were to purchase, say, 150, the marginal cost would go down greatly, and $8 is low enough that I'm still happy to give them to folks at career fairs.
sohyeon 1mo ago
Cool project :D
bimmpoke 1mo ago
i saw card with MCU (Mavel)? after i click the link and i know im wrong.
rramadass 1mo ago
> 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 https://sensor.cs.washington.edu/research/wisp_1 Perpetually Powered Energy Harvesting Systems Using the MSP430 MCU - https://www.ti.com/video/3870842958001 https://www.ti.com/video/3870842958001
- laruss5 1mo ago
  [dead]
sciencesama 1mo ago
there was a samsung cover which can even program the chip so you can actually show smily faces etc !

231 points by WilsonHarper 1mo ago

thenthenthen 1mo ago

Nice write up!

danshagen 1mo ago

cool project, especially as a bachelor student of EE!

WilsonHarper 1mo ago
Thank you, I appreciate it!

chews 1mo ago

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.

deleted 1mo ago

[deleted]

badatnames 1mo ago

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

yegle 1mo ago

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.

nielsole 1mo ago
Different idea: https://hackaday.com/2024/06/06/2024-business-card-challenge-tiny-midi-keyboard/ https://hackaday.com/2024/06/06/2024-business-card-challenge...

entrepy123 1mo ago

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...

WilsonHarper 1mo ago
I wondered if people would be interested in purchasing them. The challenging part is that they become cheap only when ordering large quantities, and most fab houses consider a different silkscreen to be an entirely different job. I'd have to order, say, 500 blanks, and then print onto them myself. Maybe there's a market for that -- but it's open source, so it's not too hard to make your own :)

adrianwaj 1mo ago

"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.

HawtAds 1mo ago
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.
- adrianwaj 1mo ago
  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.

Sorrel47 1mo ago

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

Neywiny 1mo ago
What do you mean? What's in your wallet that's an NFC transmitter?

basil_io 1mo ago

[dead]

myshapeprotocol 1mo ago

[dead]

ironqcold 1mo ago

[dead]

m4rtink 1mo ago

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

jacquesm 1mo ago

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.

WilsonHarper 1mo ago
Thanks! Most datasheets seem a bit vague when it comes to listed power output, probably because conditions can vary so much between devices and environments.

k7peak 1mo ago

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

WilsonHarper 1mo ago
Thank you! I recently earned my General license :D

cowthulhu 1mo ago

I would be really interested to know the cost per card, both at the single card volume as well as the 30 the author ended up getting.

officialchicken 1mo ago
Me too, despite being delightfully surprised by the BOM widget in the article.
- WilsonHarper 1mo ago
  The total came to roughly $150 for the cards and another $100 for shipping + import fees -- so roughly $8 each. That's more than I hoped, but the ENIG finish, 0.8mm thickness, and higher-quality silkscreen added up. If I were to purchase, say, 150, the marginal cost would go down greatly, and $8 is low enough that I'm still happy to give them to folks at career fairs.

sohyeon 1mo ago

Cool project :D

bimmpoke 1mo ago

i saw card with MCU (Mavel)? after i click the link and i know im wrong.

rramadass 1mo ago

> 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 https://sensor.cs.washington.edu/research/wisp_1 Perpetually Powered Energy Harvesting Systems Using the MSP430 MCU - https://www.ti.com/video/3870842958001 https://www.ti.com/video/3870842958001

laruss5 1mo ago
[dead]

sciencesama 1mo ago

there was a samsung cover which can even program the chip so you can actually show smily faces etc !