Last year I saw this video on Youtube that featured a 7-Color E-Paper display from Waveshare. I immediately thought it was cool and after seen the Slowmovie project by Mike Szczys I had to make my own.
As far as I know, nobody has made something like this with a color E-Paper display so even if it isn't a new concept, it brings a new twist to the game.
The plan is to make a standalone battery-powered device in a nice 3D printed case. It has to be as low power as possible since I want the batteries to last at least a couple of months. I haven't decided yet on what battery chemistry to use, the two candidates are lithium-ion or rechargeable NiMH AA. If I go with lithium-ion it will be rechargeable via USB, otherwise, AA batteries will have to be replaced when empty.
Eventually, I plan on making a custom PCB with all the components, but for the initial prototype/proof of concept, I'll be using an STM32F4 Discovery board. The following picture shows the connections between the SD-Card, the display, and the development board.
E-Paper displays ara ideal for this task because they draw power only when the image is changing. The display module comes mounted on a breakout board that converts the flat flex cable into a convenient connector, but it also has some additional circuitry. When the RST line is held LOW a MOSFET in series with the VCC line cuts power to the module. The SD-Card on the other hand as a non-zero quiescent current and so to prolong battery life, a switch must be added. This is not shown in the schematic because I will focus on the firmware side first: reading files from the SD-Card, decoding the jpeg images, dithering algorithms to increase the available number of colors.