Card Reader Contact Signal Sampling for Smartcard Stability
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Solution Overview
Problem
In smartcard-based systems, especially in pay-television, the detection of stable electrical contact between the card and card reader is challenging due to mechanical vibrations, leading to noise in the contact signal and potential erroneous system resets, making the system vulnerable to hacking during the delay before a system reset.
Innovation Solution
A card reader system that periodically samples the contact signal every millisecond for 64 milliseconds and counts the number of high samples to determine if stable contact has been established, with a system reset occurring if the count exceeds a threshold, thereby minimizing the time to determine stability and reducing erroneous resets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a long time delay is allowed to pass or a filter arrangement is provided to ensure card bouncing has ceased before analyzing the contact signal, then the reliability of contact detection is improved, but the system becomes vulnerable to hacking and the reset process is delayed
Solution Approach 1:
The patent applies periodic sampling of the contact signal at predetermined intervals (e.g., every millisecond) during a detection period. Instead of continuously monitoring or waiting for a long delay, the system periodically checks the signal state and counts consecutive high states to determine stable contact, thereby reducing the overall detection time while maintaining reliability.
Solution Approach 2:
The system uses feedback by counting the number of consecutive high signal states observed during periodic sampling. When the count exceeds a predetermined threshold, the system determines that stable contact has been established and triggers the reset process. This feedback mechanism allows for rapid and reliable detection without requiring long delays or complex filter arrangements.
2Loss of time
If periodic sampling of the contact signal is performed to determine stability, then the system reset time is reduced, but brief periods of transient stability may cause multiple erroneous system resets
Solution Approach 1:
The patent extracts only the essential information needed for reliable detection by counting consecutive high signal states during periodic sampling. Instead of reacting to every transient signal change, the system extracts the pattern of sustained high states and uses this extracted information to trigger resets only when the count exceeds a predetermined threshold, thereby eliminating erroneous resets caused by transient stability.
3Productivity
If the contact signal is analyzed immediately upon insertion to perform rapid system reset, then the productivity of the system is improved, but the mechanical vibrations and noise cause erroneous detection
Solution Approach 1:
The patent applies partial action by performing periodic sampling at specific intervals rather than continuous monitoring, and by requiring a threshold number of consecutive high states rather than reacting to every signal change. This partial approach reduces the impact of mechanical vibrations and noise while maintaining rapid detection capability, thereby improving productivity without sacrificing reliability.
Data Source
AI summary
A card reader reads data stored on a card. A contact signal is produced whose state is indicative of the presence or absence of electrical contact between the card and the card reader. A high state indicates the presence of electrical contact and a low state indicates the absence of electrical contact. Upon insertion of the card into the card reader, vibrations and other mechanical perturbations of the card cause the state of the contact signal to fluctuate rapidly between high and low states. The state of the contact signal is periodically sampled for a predetermined period of time and the number of samples for which the contact signal was high are counted. If the number of high samples exceeds a threshold then stable electrical contact is deemed to have been established between the card and the card reader and a system reset is performed.