Radio-controlled Wristwatch Week Number Overflow Handling
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Solution Overview
Problem
Radio-controlled wristwatches that receive satellite signals from GPS systems face challenges in accurately updating day-related information, such as Week Number (WN), due to overflow issues after 1,024 weeks, leading to incorrect date and day-of-the-week displays, especially when power supply voltage drops or the timekeeping circuit halts.
Innovation Solution
The wristwatch incorporates a cycle-number updating circuit and nonvolatile memory to store and update the WN cycle number, even when the power supply voltage drops, using a microcomputer to manage timekeeping and radio wave reception, and a write inhibition circuit to prevent data loss during voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the wristwatch uses GPS satellite signals for timekeeping, then the time information can be obtained globally, but the Week Number overflow causes incorrect date and day-of-the-week display
Solution Approach 1:
The wristwatch stores the last received Week Number and date information in memory before a power interruption occurs. When power is restored, the microcomputer retrieves this stored information and uses it to correctly interpret the new Week Number received from GPS, even if the Week Number has wrapped around to a smaller value. This preliminary storage action enables accurate date calculation despite the overflow issue.
2Measurement precision
If the microcomputer continuously updates timekeeping data, then accurate time information is maintained, but power consumption increases and voltage drops may cause data loss
Solution Approach 1:
Instead of continuously updating time data, the wristwatch receives and updates GPS time information periodically at scheduled intervals. The microcomputer maintains accurate timekeeping by incrementing the time counter between updates using the stored date and Week Number information. This periodic update approach reduces power consumption while maintaining time accuracy, and the stored information ensures continuity even during power interruptions.
3Reliability
If the wristwatch stores Week Number and date information in memory, then date accuracy is maintained through power interruptions, but the device complexity increases
Solution Approach 1:
The timekeeping data is segmented into distinct components: the Week Number received from GPS, the date information stored in memory, and the time counter maintained by the microcomputer. This segmentation allows each component to be managed independently, with the stored date and Week Number working together to resolve the Week Number overflow issue without requiring complex integrated solutions.
4Duration of action of stationary object
If the wristwatch uses a secondary battery for power supply, then continuous operation is enabled, but voltage drops may occur and prevent proper data writing
Solution Approach 1:
The wristwatch stores critical timekeeping data (date and Week Number) in non-volatile memory before power interruptions occur. This preliminary storage ensures that when voltage drops or the battery is depleted, the essential information needed to interpret future GPS Week Numbers is preserved. The microcomputer uses this pre-stored information to maintain date accuracy even when power conditions are unfavorable for continuous operation.
Data Source
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AI summary
Provided is a radio-controlled wristwatch that receives a radio wave including day-related information from a satellite within a global positioning system, in which a cycle number of the day-related information is correctly updated even in a case where a power supply voltage drops. A radio-wave wristwatch (1) according to the present invention includes: reception means (11) for receiving a radio wave from a satellite and extracting day-related information therefrom; timekeeping-circuit halting means for halting an operation of a timekeeping circuit based on a power supply voltage; timekeeping-circuit halt detection means for detecting that the operation of the timekeeping circuit (13) has been halted by the timekeeping-circuit halting means; a nonvolatile memory (23) for storing the day-related information and a cycle number of the day-related information; and cycle-number updating means for updating, when the timekeeping-circuit halt detection means detects that the operation of the timekeeping circuit has been halted, the cycle number of the day-related information based on a comparison result between the day-related information extracted by the reception means (11) and the day-related information stored in the nonvolatile memory (23).