LED Technology


Gesture recognition development platform


Figure 2: Example of a colour palette for an RGB LED display. (Image source: Lumex) add another colour, like red.


EPDs combine thin film transistor (TFT) technology with a layer of electronic ink. The ink comprises millions of tiny capsules containing electrically charged pigment particles. The ink is between two electrodes (Figure 3). Applying the needed drive to the TFT matrix causes the pigment particles to form a detailed image. Once


the pigment particles have been moved into place, they remain there with no power applied. Driving EPDs can be a little tricky. The front panel laminate (FPL) varies slightly from batch to batch, requiring that the drive waveform be manually tuned. In addition, different drive waveforms can be required under different operating temperatures.


Figure 3: E-ink comprises millions of tiny capsules containing electrically charged pigment particles placed between two electrodes. (Image source: Pervasive Displays)


Gesture recognition


LEDs and EPDs can provide information to system users and operators. That’s only half of a complete HMI installation. Users and operators also need the ability to provide inputs and control signals to the system. In some applications, proximity sensing alerts the system to the presence of an operator, and the display automatically turns on to provide status information. While that’s useful for sending status information, it does not provide a mechanism for sending inputs and commands to the equipment. Using traditional keyboards, switches, and other mechanisms can be an option but can result in relatively large and power-hungry solutions. Instead, designers can turn to gesture recognition interfaces for proximity sensors to detect and translate hand movements and patterns into commands. Gesture recognition can be especially useful for noisy environments, where the background noise and ambient sounds make it difficult to use voice recognition. It takes three activities to implement basic gesture recognition:  Recognising the beginning and end of a gesture


 Tracking hand movement throughout the gesture


 Using the information from the first two steps to understand the gesture


Figure 4: The ADPD2140 IR light angle sensor has a linear response within a ±35° angular field of view. (Image source: Analog Devices)


To develop a gesture recognition system, designers can turn to Analog Devices’ EVAL- CN0569-PMDZ reference design based on the ADPD2140 IR light angle sensor. The circuit emits an IR pulse train, and the sensor captures the reflected light. The design supports gesture sensing up to about 20 centimetres (cm) away from the board. The sample rate of up to 512 samples per second enables designers to adjust the noise rejection and response time to best suit the application and environment. Also noteworthy is that the ADPD2140 does not require precise alignment; its sensor has a linear response within a ±35° angular field of view (Figure 4). The integrated optical filter in the ADPD2140 package provides a sharp cutoff of visible light, further simplifying system design by eliminating the need for external lenses or filters while maintaining the dynamic range of the sensor under bright indoor lighting or sunlight.


Alphanumeric LED displays Applications that need bright and rugged alphanumeric LED displays can turn to designs with parallel interfaces or serial interfaces from Broadcom. The displays with parallel interfaces are available with 4 or 8 characters (Figure 5). They are available in several package styles, colours, and sizes, such as the 8-character, 5-millimetre (mm) HDSP- 2533 with green LEDs and the 4-character, 3.7 mm HDLU-1414 with high-efficiency red LEDs, both in plastic packages. Or the 8-character, 5 mm, HDSP-2131 with yellow LEDs in a rugged glass/ceramic package. All include an integrated ASIC driver simplifying the design effort. Features of these parallel interface displays include:  Seven to eight bus lines for data  Character map with 128 ASCII and sixteen user-definable characters stored in programmable ROM


Figure 5: Alphanumeric LED displays with parallel interfaces are available with 4 or 8 characters. (Im- age source: DigiKey)


continues on page 48 www.cieonline.co.uk Components in Electronics February 2024 47


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