Optical Keypad Modulation Through Thick Glass in Explosive Areas
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Solution Overview
Problem
Existing optical keypads face challenges in reliability and security, particularly in hazardous environments, due to interference from collocated devices, smooth surfaces, daylight, and artificial light, which affect keystroke detection accuracy and security.
Innovation Solution
The optical keypad employs a combination of infrared LEDs, a photo diode, and adaptive filtering techniques, including pseudo-random modulation and polarized light filtering, to minimize interference and ensure reliable keystroke detection through a thick glass panel, using adaptive gain and threshold adjustments to account for environmental variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If optical keypad uses simple light transmission detection, then device complexity is reduced, but reliability and security deteriorate due to interference from external light sources and collocated devices
Solution Approach 1:
The patent applies periodic modulation of the transmitted light signal at a specific frequency (e.g., 1 kHz square wave modulation). The receiver detects the modulated signal and demodulates it to identify valid keystrokes. This periodic action distinguishes intentional key presses from random external light interference, thereby improving reliability without significantly increasing device complexity.
Solution Approach 2:
The patent changes the frequency parameter of the transmitted light signal to create a unique identification code for each keypad. By assigning different modulation frequencies to different keypads, the system can distinguish between signals from collocated keypads, preventing cross-talk and improving detection accuracy while maintaining relatively simple hardware.
2Reliability
If optical keypad operates in hazardous environments with thick glass panels, then safety certification is achieved, but measurement precision deteriorates due to light attenuation and interference
Solution Approach 1:
The modulated light signal allows the receiver to detect specific frequency patterns even after transmission through thick glass panels (8-12mm). The periodic modulation creates a distinctive signal signature that can be identified against the background of attenuated and scattered light, maintaining measurement precision despite the safety-certified thick glass requirement.
Solution Approach 2:
The patent replaces simple intensity-based detection with frequency-based detection. By substituting the detection mechanism from measuring light amplitude to measuring light frequency/modulation patterns, the system can penetrate thick glass panels more effectively and distinguish valid signals from environmental interference, maintaining precision while meeting safety standards.
3Adaptability or versatility
If multiple keypads are collocated, then device versatility is improved, but cross-talk interference increases between adjacent keypads
Solution Approach 1:
The patent assigns different frequency parameters to different keypads or different keys within keypads. Each keypad operates at a unique modulation frequency, creating a frequency-division multiplexing scheme. This allows multiple keypads to operate simultaneously without cross-talk, as the receiver can filter and identify signals based on their specific frequency signatures, thereby supporting multi-keypad versatility.
Solution Approach 2:
The patent segments the frequency spectrum into distinct channels, with each keypad or key assigned to a specific frequency range. This segmentation of the operating parameter space allows multiple keypads to coexist without interference, as each operates in its own frequency niche. The receiver can selectively tune to different frequency segments to detect keystrokes from specific keypads.
4Ease of operation
If simple light detection is used, then ease of operation is improved, but susceptibility to daylight and artificial light interference increases
Solution Approach 1:
The modulated light signal creates a periodic pattern that is easy to implement but powerful in rejecting environmental interference. The receiver looks for signals with the specific modulation frequency, automatically filtering out constant or non-modulated ambient light from daylight and artificial sources. This maintains ease of operation while dramatically improving immunity to environmental light interference.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution provides a highly reliable and secure keypad that resists interference from nearby devices and external light sources, ensuring accurate keystroke detection even in hazardous environments, meeting ATEX and UL/CSA certification standards.
Implementation Method 1
a plurality of light-emitting diodes (LEDs) emitting modulated light and at least one receiving photo diode placed in relation to the apertures, which light from the transmitting LEDs is transmitted through the transparent panel
Implementation Method 2
which reflected modulated light is transmitted back through the transparent panel and back to the receiving photo diode for demodulation
Implementation Method 3
the light transmitted from the LEDs can be filtered with respect to optical polarisation to one state of polarisation, and the light incident on the photo detector is filtered to the perpendicular state of polarisation relatively to the transmitted light
Implementation Method 4
which light is reflected by scattering from a tool or fingertip employing a keystroke in relation to one of the apertures in the transparent panel
Data Source
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AI summary
The present invention relates to an optical keypad for use in hazardous areas, which optical keypad can ensure a safe and reliable detection of a keystroke. It is the object of the invention to be capable of detection of a keystroke through an at least 8 mm thick glass window, which is required for electronics equipment located in hazardous explosive areas (In accordance with ATEX Directive 94/9/EC and similar requirements). The object can be fulfilled by a system, where at least 6 LEDs are lit in a pseudo-random sequence, modulated by a pseudo-random frequency and the interval between the lit of each LEDs are change randomly to avoid interference between collocated keypads and light from other sources as daylight and artificial light.