WisBlock E-Paper Displays

Part 2 in my Exploring Wisblock series

I’ve been working with e-paper displays for a few years, starting with the PaPirus Raspberry Pi HAT and more recently with Waveshare 2.7 inch e-paper HAT. The Papirus seemed to have quality issues and over time the displays would deteriorate. I have not had any significant problems with the Waveshare displays. For my application (earthquake sensors) the fact that they retain the display without power is very appealing. Without power or internet after a large earthquake it may be some time before they can be read and the battery may be exhausted. The information on the display is important in deciding whether the building is safe to enter.

RAK Wireless offers two variants of the same display – one that is black and white and one that is black/white/red. I have worked with black/white/red displays before and the display looks very nice but it takes a long time to refresh. So I ordered one of each. The boards come with three button attachments. The e-paper displays and buttons are connected to the RAK14000 driver boards by flexible FPC cable connectors.

When I used the PaPirus displays they had a similar FPC cable connecting the e-paper display and driver board. I found that was a problem as over time that connection sometimes came loose or the tiny piece of plastic that keeps the cable in place came loose or broke. So my first impression was not very positive. And as I suspected two of the sockets broke – the tiny hinged closing mechanism broke off.

The other problem I could immediately see was how to mount the displays. the displays are thin pieces of glass with no frame or mounting mechanism So I could see that would be a challenge.

RAK provides sample code to drive the displays but I could not get anything to show up on either display. the buttons worked, but nothing on the display. But with the ribbon cable issues and potential mounting problems I decided to move on. These displays use IO1 and IO4 pins in addition to the SPI interface, which is unfortunate since that restricts using slots A, B and C for other sensors. Slots A and B use IO1 and IO2, and Slot C uses IO3 and IO4. That only leaves Slot D on a standard RAK19007 base board. It’s too bad they didn’t use IO3 and IO4 which would free up Slots A, B and D. That may be the reason I had problems with the display – there may have been a conflict.

Anyway my plan is to use one of the Waveshare e-paper displays which use SPI plus two IO pins. Unfortunately the SPI pins are not exposed on the RAK19007 Base board but all the pins are available on the RAK19001 Dual IO Base board. More about that in a future post.