Mobile Keypad Backlight Adjustment via Light Sensor Hysteresis
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Solution Overview
Problem
Conventional backlit keypads experience readability issues due to contrast inversion in ambient lighting conditions, where characters become illegible as the contrast ratio decreases below a certain threshold in 'dim' lighting conditions, occurring between daylight and darkness.
Innovation Solution
A method for automatically adjusting keypad brightness on a mobile device using a light sensor to turn the backlight on when the ambient light level falls below a threshold and off after a predetermined period, maintaining a suitable contrast ratio by introducing a hysteresis loop to avoid flickering and ensure legibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the backlight is turned on in dim lighting conditions, then keypad visibility is improved, but contrast ratio decreases leading to illegible characters
Solution Approach 1:
The system dynamically changes the backlight intensity parameter based on ambient light conditions. By adjusting the backlight intensity rather than simply switching it on/off, the system maintains optimal contrast ratio while ensuring visibility in dim lighting conditions
Solution Approach 2:
The system uses a light sensor to continuously monitor ambient light levels and provides feedback to the backlight controller. This closed-loop feedback mechanism enables the system to automatically adjust backlight intensity to maintain optimal contrast ratio across varying lighting conditions
2Illumination intensity
If the backlight is turned on continuously to ensure readability, then visibility is maintained, but energy consumption increases
Solution Approach 1:
The system transitions from a static backlight state (always on or always off) to a dynamic state where backlight intensity continuously adapts to ambient lighting conditions. The backlight is activated only when ambient light levels indicate reduced visibility, optimizing the balance between readability and energy consumption
Solution Approach 2:
The system changes the backlight intensity parameter dynamically based on ambient light sensor readings. By adjusting intensity rather than using binary on/off control, the system reduces energy consumption while maintaining adequate visibility during transitional lighting conditions
3Adaptability or versatility
If the backlight switches rapidly in response to ambient light changes, then adaptability is improved, but flickering occurs reducing user experience
Solution Approach 1:
The system applies a threshold-based preliminary action mechanism where backlight switching is triggered only when ambient light levels exceed or fall below predetermined thresholds. This prevents rapid switching in transitional lighting conditions and eliminates flickering while maintaining adaptability to significant lighting changes
Solution Approach 2:
The system implements periodic sampling of ambient light levels with a defined threshold hysteresis band. By requiring sustained light level changes beyond the threshold before triggering backlight switching, the system creates a stable periodic response pattern that prevents flickering
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
The method effectively maintains a contrast ratio suitable for legibility by turning the backlight on when necessary and off before contrast inversion occurs, preventing readability issues and ensuring optimal visibility in varying lighting conditions.
Implementation Method 1
A method for automatically adjusting keypad brightness on a mobile electronic device having a light sensor, keypad and backlight for the keypad
Data Source
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AI summary
A method is set forth for automatically adjusting keypad brightness on a mobile electronic device having a light sensor, a keypad and a backlight for said keypad, comprising obtaining light level samples from the light sensor, turning the backlight from off to on in the event a current light level sample is less than a threshold value below which backlight illumination becomes necessary in order to read the keypad, and from off to on after a predetermined time period in the event the current light level sample is greater than the threshold value.