Photodiode Reset Input Circuit for Low-Power Light Blocking Detection
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Solution Overview
Problem
Existing devices require reliable and low-power input elements, especially for hardware reset functions that must operate without software interference, and current photodiode-based solutions are not optimized for low power consumption and simplicity.
Innovation Solution
A device with a user-operatable input element featuring a sensing circuit comprising a first and second photodiode arranged in series, where the photodiodes are spaced apart to receive ambient light through separate areas of the housing, allowing the user to block light and detect input through an amplifier circuit, with a non-transparent cover for the second photodiode to enhance sensitivity and low power operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a photodiode-based input element is used, then the device can detect user input through light blocking, but the power consumption increases and the device becomes more complex
Solution Approach 1:
The patent changes the operating parameters of the photodiode circuit by using a current-to-voltage converter amplifier that operates at very low current levels (0.2 µA). The circuit converts the photodiode's current output to a voltage signal that can be detected by the microcontroller, enabling reliable input detection while maintaining extremely low power consumption. This parameter transformation allows the system to achieve both reliability and low power usage.
2Adaptability or versatility
If software-based input detection is used, then the device can adapt button functions, but the device cannot function as a last resort reset when non-responsive
Solution Approach 1:
The patent segments the input detection function into two independent parts: a hardware-based photodiode detection circuit for critical reset functionality, and software-based button detection for adaptive functions. The hardware circuit directly triggers a reset interrupt that bypasses the operating system, ensuring it works even when the software is unresponsive. This segmentation allows both adaptability and reliable hardware reset capability to coexist.
3Measurement precision
If multiple photodiodes are arranged in series, then the sensing circuit can detect light blocking, but the device complexity increases
Solution Approach 1:
The patent introduces a current-to-voltage converter amplifier as an intermediary component between the photodiodes and the microcontroller. This amplifier converts the small current changes from the photodiodes into a voltage signal that is easier to process. The intermediary simplifies the overall circuit design by providing a standardized voltage output that can be directly read by the microcontroller's ADC, reducing the complexity of signal processing requirements.
4Ease of operation
If the photodiodes are spaced apart to receive light through separate areas, then the user can block light selectively, but the housing area required increases
Solution Approach 1:
The patent arranges the two photodiodes in a vertical stacking configuration rather than placing them side-by-side horizontally. Both photodiodes receive light through the same housing area via a shared light guide or optical path, but they are positioned at different depths (z-dimension). This vertical arrangement allows selective light blocking by the user while minimizing the horizontal footprint on the housing surface, effectively using the third dimension to resolve the space constraint.
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 provides a low-cost, waterproof, and hardware-only input element with very low power consumption (0.2 µA), suitable for use as a reset switch without software support, capable of functioning in various lighting conditions.
Implementation Method 1
A sensing circuit comprising at least one first photodiode and at least one second photodiode
Data Source
Figure 1~2
Figure 3~6
AI summary
The device has an input element (14), which can e.g. be used for resetting the device. The input element (14) has at least one first photodiode (D1) arranged in series to at least one second photodiode (D2a, D2b). A voltage (U) is applied over the photodiodes (D1, D2a, D2b). When the user blocks light to only the second photodiode (D2a, D2b), the voltage at the interconnection between the photodiodes changes, which can be used to trigger the input element (14). The input element has low power consumption and high reliability.