7.5-inch e-ink display is powered completely by NFC

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  The e-ink display is a bit grainy thanks to the 800x600 resolution. [credit: Waveshare ]

NFC is usually only used to for quick text transfers, like a tap-and-pay transaction at a register or a quick data transfer from an NFC sticker. A company called "Waveshare" is really pushing the limits of NFC, though, with a 7.5-inch e-ink display that gets its data, and its power, from an NFC transfer. The $70 display doesn't have a battery and doesn't need a wired power connection.

E-paper (or e-ink) displays have the unique property of not needing power to maintain an image. Once a charge blasts across the display and correctly aligns pixels full of black and white balls, everything will stay where it is when the power turns off, so the image will stick around. You might not have thought about it before, but in addition to data, NFC comes with a tiny wireless power transfer. This display is designed so that NFC provides just enough power to refresh the display during a data transfer, and the e-ink display will hold onto the image afterward.

NFC's power transfer works just like wireless phone charging: the reader (probably your phone) generates an RF field to transfer power to the passive NFC object. NFC stickers (and any other NFC device) have a sizable spiral antenna to harvest the RF signal, just like a wireless charging coil. The amount of power you can transfer over NFC depends on the design of the object and the reader, but Waveshare warns that some phones might not put out enough power. If your phone doesn't work, the company recommends an NFC board that puts out 1.4 watts of power, but Waveshare also shows the device working with a pretty old Android phone, a Samsung Galaxy S7 Edge from 2016.

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