back in 2015 some researchers came up with an e-ink display device which was powered entirely by harvesting joules from the NFC connection your phone used to talk to it, and I’m honestly kind of shocked these aren’t all over the place now? alansonsample.com/research/NFC

@ticky for what purpose? I guess they could be nifty rewritable labels on keys or sth but I don't see any super-obvious use case

@Goldkin @noiob 100% absolutely (the linked article even demonstrates briefly charging its capacitor, before using it for temperature data logging!)

@noiob @ticky In all seriousness, the most commonly cited use case I've seen is inventory control tags, which I think are in use today but not widely used at retail.

@Goldkin @noiob yeah, I haven’t seen this type, I think because manually updating would be an enormous undertaking, though I have seen ones with a little coin cell which check in over Wi-Fi periodically, which seems a reasonable compromise!

@ticky @Goldkin over here stores are using small eInks or LCDs as price tags that get updated over Wifi, apparently it's not super easy to update them without wasting too much power, which is why one of the methods involves turning off the in-store wifi for a short time so the tags can be reached

@ticky @Goldkin I've been wanting to get some but the setups are of course super expensive

@noiob @Goldkin yeahhhhh everything is industrial grade and priced accordingly 😬

@ticky @Goldkin like I just want a few tags and a way to send data to them from my raspberry pi

@noiob @ticky My own method of doing so has been connecting Pi Zero Ws to a display via GPIO pins, scraping image data from a web daemon are home. Hardware cost is ~$60 per tag though, which isn't cheap unless you buy bulk supply.

@noiob @ticky Requires a source of power over USB as well. Battery on my solar graph was an extra $50, but provides its own solar power to the Pi independent of my power grid at home.

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