Optical Rain Sensor LED Current Balancing With Fine Pulse Adjustment
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Solution Overview
Problem
Existing optical rain sensors face challenges in accurately detecting rain or moisture due to imbalances in LED signals, which can lead to false detections caused by sensitivity changes from sunlight exposure, and lack sufficient current resolution to correct these imbalances.
Innovation Solution
An optical rain sensor device with a regulated current source that allows for fine adjustment of the driving currents of light emitting elements, using a microcontroller to output a compensation current signal to balance the total current across the LEDs, reducing imbalances and mitigating false detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a coarse current adjustment with +/- 2.5 mA step is used to control LED driving current, then the device complexity is reduced and ease of manufacture is improved, but the measurement precision of LED signal balance deteriorates and false detections increase
Solution Approach 1:
The current adjustment is segmented into two independent stages: coarse adjustment (±2.5 mA steps) and fine adjustment (±0.25 mA steps). This segmentation allows each stage to optimize for its specific function - the coarse stage for ease of manufacture and the fine stage for measurement precision, resolving the contradiction between manufacturability and precision.
Solution Approach 2:
The system dynamically switches between coarse and fine adjustment modes based on the detected imbalance magnitude. When large imbalance is detected, coarse adjustment is applied first; when small imbalance remains, fine adjustment takes over. This dynamic approach optimizes both manufacturing simplicity and detection precision across different operating conditions.
2Reliability
If a fine current adjustment with higher resolution is implemented to correct LED signal imbalances, then the measurement precision and false detection rate are improved, but the device complexity increases
Solution Approach 1:
The adjustment system is segmented into two independent adjustment circuits - a coarse adjustment circuit and a fine adjustment circuit. Each circuit is optimized for its specific resolution range, allowing the system to achieve high overall precision without requiring a single complex high-resolution circuit throughout the entire adjustment range.
Solution Approach 2:
The fine adjustment circuit provides excessive precision (±0.25 mA) that exceeds what would be needed if used alone. However, this excessive precision is only activated when necessary (when small imbalances remain after coarse adjustment), keeping the overall system complexity manageable while ensuring detection accuracy when needed.
3Ease of operation
If LED channels are driven with equal current to simplify control, then the ease of operation is improved, but the reliability deteriorates due to inherent LED signal imbalances causing false detections
Solution Approach 1:
The system performs preliminary balancing of LED channel currents before actual rain detection begins. By pre-adjusting the current in each LED channel to compensate for manufacturing variations and aging effects, the system ensures that both channels start with balanced signals, eliminating the source of false detections while maintaining simple equal-current control during normal operation.
Solution Approach 2:
The system implements feedback control by continuously monitoring the balance between LED channel signals and automatically adjusting the current distribution accordingly. The microcontroller measures the photodetector signals from both channels and uses this feedback to dynamically adjust the current through the coarse and fine adjustment circuits, maintaining reliability without complicating the control interface.
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 solution effectively reduces false detections by achieving precise current adjustments, ensuring detection accuracy independent of sunlight exposure and improving the balance between LED signals, thereby enhancing the reliability of rain detection.
Implementation Method 1
The detection principle of optical rain sensors is based on detecting the portion of infra-red light emitted by one or more light emitting sources that is reflected from an internal surface of a transparent substrate
Implementation Method 2
Total internal reflection will be reduced in the presence of a drop on the outward surface, due to the refraction of light through the transparent substrate 130 and the drop
Implementation Method 3
first and second light emitting elements adapted to emit first and second light pulses towards an inner surface of a transparent substrate
Data Source
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AI summary
The present invention relates to a real-time, fine adjustment of light emitting device current in an optical rain sensor using an external regulated current source. The regulated current source comprises: a variable current source to supply an output current (lout) with a constant intensity that is adjustable based on an external regulation signal; a controlled switch to be connected between a terminal of the light emitting device and said output terminal of the variable current source. The controlled switch is adapted to switch between an on state and an off state in synchronization with the driver current pulse supplied to the light emitting element for connecting and disconnecting said variable current source, thereby generating a compensation current signal (Ic) based on said regulation voltage (Vreg) and that is superimposed on the driver current pulse across the light emitting device for reducing an imbalance between the first and second light pulses.