Aaron Christophel Delves Deep Into Waveshare's Passive NFC ePaper Displays to Write Custom Firmware

Maker Aaron Christophel has published a tool for taking full control over the low-cost passive Near Field Communication (NFC)-driven ePaper displays available from embedded hardware specialist Waveshare — reverse-engineering the undocumented system-on-chip inside.

"Waveshare provides an example app and also an SDK [Software Development Kit] to build your own Android app where you can just place your mobile device or any NFC device onto the display and it will refresh it," Christophel explains of the devices. "While Waveshare is quite open about what is the way to drive them, they do not really disclose any info on what part is inside."

Looking to take more direct control over the devices — which offer a wire-free way to update the displayed image, harvesting enough energy from an NFC transmitter to update the electrophoretic ePaper display — Christophel set about figuring out what was going on inside. That, it turned out, was a Chivotech TN2115S2 system-on-chip, for which a datasheet exists with enough information to get started.

Dumping the content of the chip, Christophel turned to the Ghidra disassembler to reverse-engineer the functions required for driving the display. With that, the maker was able to create his own custom firmware — loadable using a Segger J-Flash Lite set to an Arm Cortex-M0 target.

This is, of course, far from Christophel's first time experimenting with ePaper tags. Three years ago he demonstrated an Espressif ESP32-based tool which served to control common electronic shelf label (ESL) ePaper displays, followed by a way to flash ones built around Texas Instruments' CC8051. He's also known for putting them to use in projects ranging from low-power desk clocks to person-scale wall-art.

Christophel has released source code and a precompiled binary for the project on GitHub under the reciprocal GNU General Public License 3, to accompany the video embedded above.