The first time I saw a wireless electronic shelf label, it was virtually indistinguishable from the old-fashioned paper labels I was accustomed to. I only realized it was electronic when the price changed before my eyes. These electronic paper displays (EPDs) are changing the retail game. What once took hours or even days, with a person walking around manually updating shelf labels and industrial signage, can now be done in seconds. The EPDs have reflective properties that only require ambient light to be visible, meaning they don’t have the glare of typical electronic displays. This makes the displays more like the pages of an e-reader that mimics what it’s like to read a paper book. They are also bistable, which means they can retain an image even when no power is connected.
The pixels of an EPD are composed of millions of tiny microcapsules, each about the diameter of a human hair. E Ink, a pioneer in electronic signage, developed its 3-pigment ink system specifically for electronic shelf labels. It works by applying a charge to the pigments and to a top and bottom electrode to facilitate movement. Since EPDs have the ability to draw zero current, the power consumption of the microcontroller unit (MCU) and the rest of the application is very low, and therefore, ideally suited for these applications.
Our EFR32 MCU is a great fit for EPD applications due to its energy efficiency and storage capacity. To help developers get started, we’ve put together this Application Note showing how to drive an EPD with the EFR32xG22-based Wireless Starter Kit. You can also find more info on our GitHub page. The flexible energy modes of the EFR32 allows the MCU to draw as little current as possible and in many cases the MCU’s Energy Mode 4 can be used, resulting in power consumption as low as 170 nA. Memory is another important feature for saving frame buffers and images and the EFR32 has large memory options, both for Flash and SRAM. This application note also makes use of E Ink’s EPD extension board, which is available along with a HULK Driving Board here.
Even though the EPDs draw no current while showing a static image, they require a significant amount of current while updating the display, which is the only time they consume any power. An update can take between 12-18 seconds at room temperature, and aside from the time requirements, the MCU must complete the power-up/power-down sequences and transmit frames to the panel. For this reason, EPDs are not suited to applications that require a high update frequency.
The app note discusses ways to optimize power consumption during a display update, including putting the MCU into its optimal energy mode. Learn more about how electronic shelf labels contribute to retail infrastructure here, and if you set out to develop an EDP, we’d love to hear how your project is going.