LED Technology
How to combine LEDs, e-paper, and gesture recognition for low-power HMIs in enterprise connectivity
By Rolf Horn, applications engineer at DigiKey H
uman machine interfaces (HMIs) are an important element supporting enterprise connectivity for the Industrial Internet of Things (IIoT) in
Industry 4.0 automation and process control, and automotive and medical systems. HMIs range from augmented reality goggles to touch screens and simple visual indicators. While augmented reality goggles get a lot of headlines and touch screens bring a lot of capabilities, simple, low-cost, miniature, and low-power visual indicators and controls are needed for a growing range of edge devices. Designers can combine LED dot matrix or electronic paper (e-paper) displays (EPDs) with gesture recognition and proximity sensing infrared (IR) light angle sensor controls to implement low power, low cost, and feature- rich HMIs on IIoT edge nodes in Industry 4.0 and across a range of enterprise, medical, and automotive applications.
This article begins by reviewing the operation and capabilities of alphanumeric and dot matrix LED displays and EPDs, then details the use of IR light angle sensor ICs in gesture recognition and proximity sensing. It then presents representative LED displays from Broadcom and Lumex, an EPD from E Ink, an EPD development platform from Pervasive Displays, and an IR sensing IC for gesture recognition from Analog Devices, along with development platforms to speed the design and integration process for high performance, low power, miniature HMIs.
Alphanumeric LEDs
Alphanumeric LED displays are available that accept parallel and serial data inputs and a range of character numbers, sizes, and display widths. Each character is formed from a 5 x 7-pixel array— usually using a single LED colour like red or green. These displays integrate character sets like the American Standard Code for Information Interchange (ASCII) characters, the ISO 15924 Japanese
46 February 2024
Figure 1: The ASCII character set as formed using a 5 x 7-pixel alphanumeric LED display. (Image source: Broadcom)
Katakana script character set that can be encoded in the ASCII character set, as well as country-specific characters and custom user-defined characters for special use cases (Figure 1). They can be daylight readable and environmentally rugged.
Visual LED displays
Instead of being used to form individual characters, LED dot matrix displays use LEDs arranged in a matrix layout to deliver graphics. They can also display standard ASCII, Katakana, and other text formats. In terms of performance, they are between the dot matrix displays
Components in Electronics
described above and video LED displays. They are available in a wide range of sizes and can be single-colour displays like red, green, or red green blue (RGB) multi-colour displays. However, they usually have a more limited colour palette and slower refresh rates compared with video displays (Figure 2). The LEDs are usually arranged in a grid pattern with either the negative or positive terminals of the LEDs tied together as a common circuit node. Visual LED displays are available that operate with I2C, 8-bit parallel, series, and other interfaces. Some include an onboard microcontroller unit (MCU), and others use the system processor.
What’s e-paper, and how does it work?
While LEDs require a continuous drive current to stay on, e-paper is a bistable technology that does not require continuous drive and can be extremely low power. When low power is a priority, refresh rates are low, and full colour is not needed, e-paper displays (EPDs) can provide a viable alternative to LED and liquid crystal displays (LCDs). It takes very little power to render an image on an EPD; once the image is rendered, no power is needed to maintain it. EPDs have contrast like ink and paper. While most are black and white, some
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