Solar-Powered Wristwatch Illuminance Detection Circuit
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Solution Overview
Problem
Radio-controlled wristwatches using solar cells face challenges in determining illuminance levels for efficient satellite signal reception and battery charging without directly measuring output voltage or current values, especially in varying indoor and outdoor environments.
Innovation Solution
Incorporating an illuminance detection circuit with switchable resistance values and threshold voltage switching means to determine whether the solar cell is irradiated with light above different threshold values, allowing the wristwatch to adjust its operation modes accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the wristwatch uses a single illuminance threshold criterion, then the determination process is simple, but it cannot accurately distinguish between indoor lighting and outdoor sunlight conditions
Solution Approach 1:
The single illuminance threshold is segmented into multiple thresholds (first threshold and second threshold) to create distinct detection ranges. The first threshold detects indoor lighting conditions while the second threshold detects outdoor sunlight conditions, allowing the system to differentiate between environments with high precision while maintaining simple comparison-based detection logic.
Solution Approach 2:
The illuminance detection system dynamically switches between different threshold values based on the current detection state. When the first threshold is exceeded, the system transitions to using the second threshold, enabling adaptive response to changing light conditions without complex calculation processes.
2Measurement precision
If the wristwatch directly measures output voltage or current values of the solar cell, then illuminance detection is accurate, but the device complexity increases
Solution Approach 1:
The patent introduces threshold voltage values as intermediary reference points that mediate between the solar cell's output voltage and the illuminance determination logic. Instead of directly measuring and interpreting complex voltage-current characteristics, the system compares the output voltage against predefined threshold values, significantly simplifying the measurement circuit while maintaining detection accuracy.
Solution Approach 2:
The patent replaces direct electrical measurement (voltage and current sensing) with a voltage comparison mechanism. By substituting the mechanical/electrical measurement system with a simple comparator circuit that references threshold voltages, the system achieves illuminance detection with reduced circuit complexity.
3Adaptability or versatility
If the wristwatch receives satellite signals indoors, then time correction can be performed anywhere, but signal reception intensity is insufficient
Solution Approach 1:
The satellite signal reception function is dynamically enabled or disabled based on illuminance detection results. When outdoor sunlight conditions are detected (exceeding the second threshold), the system activates signal reception to ensure reliable time correction. This dynamic control balances location flexibility with signal reception reliability.
4Duration of action of moving object
If the control circuit operates continuously with low battery voltage, then the wristwatch functions are maintained, but abnormal stop may occur due to voltage shortage
Solution Approach 1:
The system performs preliminary charging of the secondary battery when indoor lighting conditions are detected (exceeding the first threshold). By accumulating energy in advance during periods of adequate lighting, the system ensures sufficient power reserves before potential low-voltage conditions arise, preventing abnormal stops while maintaining continuous operation.
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
Enables the wristwatch to accurately determine illuminance levels without direct measurement, ensuring efficient satellite signal reception and battery charging, thereby improving outdoor signal reception and power management.
Implementation Method 1
a solar cell 41, and a power supply unit 40 that supplies power to each unit
Implementation Method 2
an illuminance detection circuit 43 that detects an illuminance level based on an output voltage value of the solar cell 41
Data Source
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AI summary
Provided is a radio-controlled wristwatch capable of determining whether or not the illuminance of light irradiating a solar cell is high on the basis of a plurality of different criteria without directly measuring an output voltage value or an output current value of the solar cell. The radio-controlled wristwatch includes: a solar cell; a control circuit which stops operation under a predetermined condition; and an illuminance detection circuit which outputs a signal indicating whether or not illuminance of light irradiating the solar cell is higher than a given threshold value. The radio-controlled wristwatch switches the given threshold value between a first illuminance threshold value and a second illuminance threshold value that is larger than the first illuminance threshold value, starts the control circuit in a stop state when a signal indicating that the illuminance is higher than the first illuminance threshold value is output, receives a satellite signal containing time information from a satellite when a signal indicating that the illuminance is higher than the second illuminance threshold value is output, and displays time corresponding to the time information contained in the received satellite signal.