Matt Gross' Move to an ePaper Display Makes for a Simpler, Lower-Power Smart Calendar
This Raspberry Pi-powered smart calendar used to rely on presence detection to save its LCD panel from burn-in — but no more.
Maker Matt Gross has built a Raspberry Pi-powered smart calendar into a picture frame — with the display handled by a 7.3" seven-color ePaper panel, for minimum power draw and maximum visual comfort.
"I had an event calendar running in a full-screen [Google] Chrome window on a [Raspberry] Pi Zero," Gross explains of the project's predecessor, which used a more traditional liquid-crystal display (LCD) panel. "While it worked well enough, I needed a motion sensor to turn on the display only when someone walked by the [Raspberry] Pi (to prevent screen burnout). After seeing some of the new multi-color [ePaper] displays, I decided that it was time for an upgrade."
Traditional transmissive LCD displays work by blocking the light from an always-on backlight, shifting their subpixels to brighten, darken, and present different colors. It's a great approach for rapidly-moving video, but not so great for static images: the backlight is constantly drawing power and if left long enough high-contrast parts of the image can "burn in" and remain permanently visible in ghost form.
An electrophoretic ePaper display, by contrast, has no backlight, typically relying on ambient lighting — providing a more paper-like viewing experience. The displays move physical "electronic ink" to shape their imagery, require no power except when changing states, and don't easily give in from burn-in from static images. The trade-off: less-vibrant colors and long refresh times of up to 30 seconds for full-color panels.
For a calendar, those aren't a deal-killer — so Gross switched across to a 7.3" seven-color ePaper panel, doing away with the presence-detection system altogether. The project was tested with a Raspberry Pi 3 Model B/B+ single-board computer and a lower-cost Raspberry Pi Zero W, Gross says, with the finished version opting for the less powerful but more compact Raspberry Pi Zero W once development was complete.
The project's bill of materials and full source code are provided on GitHub under the permissive MIT license, with more information available in Gross' Reddit post.