The main difference between EPDs-also known as e-paper displays-and conventional display types is that the former operates on a purely passive basis. This means that they have no backlighting like LCD displays and no light-emitting pixels as OLED displays do, instead relying on ambient light. This means that they are still very easily readable even in bright light and intense sunlight-basically just like real, printed paper. They are also extremely energy-efficient, as they need just a single pulse of current to display new information. Any activated pixels or segments then retain their state for as long as they are needed without consuming any energy at all.
They also offer up something special in terms of their viewing angle-content is clearly readable at up to 180° on an e-paper display, so basically from any angle.
Lives of up to 10 years make for a compelling argument for long-term projects in particular. Of course, how long these displays actually "live" for is primarily dependent on how they are used. It is important to observe the specified operating temperatures, which should not be exceeded.
Applications from Price Tags to Thermostats
These features make e-paper displays ideal for electronic price tags. They are an elegant and modern solution that also help to save costs, as they minimize the workload involved in keeping prices up to date. With e-books, the "paper white" displays combined with touch technology provide a comfortable reading experience that is easy on the eyes.
E-paper displays are also best employed wherever low power consumption is needed and display updates are rare, for example in industrial metering applications, for thermostat displays, for receivers, room signage and much more.
How E-Paper Displays Work
An e-paper display consists of many microcapsules, each measuring just a few dozen µm. These microcapsules house microscopic particles in a clear liquid-negatively charged white particles and positively charged black particles. By applying electrical fields externally, these particles can be moved around (Figure 4). The electrodes are controlled by an active matrix, each with a thin-film transistor for each pixel, just like conventional TFT displays. The response time of an e-paper display is usually several 100ms, so they are too sluggish for displaying moving video footage, but for static displays that rarely change, this is not a problem.
Bringing in Color ... Albeit Slowly
Most e-paper displays that are currently in use can display information in black & white, usually text and figures. Up to 16 shades of gray and various colors are possible. The fact that there are hardly any full-color e-paper displays is due in part to the higher price, and also due to the color quality still being poor. The suppliers are feverishly engaged in development, but this is no easy task. The technology for color displays is much more complicated than for black & white displays.
E-paper displays on the market support for black & white, black, white & red, and also black, white & yellow as standard, and companies like Holitech have also recently started offering combinations such as white & green and white & blue. This supplier's portfolio includes sizes ranging from 1.54" to 42.0", and the company also provides features on request such as touch support, glass panels or acrylic panels, as well as frontlighting.
Minew offers e-paper displays with cases, wireless modules, batteries and associated electronics as complete electronic price tags. Customers here have a choice of sizes ranging between 1.54" and 11.6". Advantech also offers selected ready-to-use modules with e-paper displays that are available in 2.9", 5.6" and 13.3" sizes with housings, batteries, boards and a wireless module.
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