Pulse-Train Reed Switch Sensing for Low Static Current
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Solution Overview
Problem
Traditional reed switch state detection methods result in significant static current draw when the switch is closed, which reduces battery life in low-power systems by dominating sleep current.
Innovation Solution
A switch sensor system utilizing programmable memory, pulse generation circuitry, and comparator circuitry that toggles a pulse-train voltage signal between active and inactive states to minimize power consumption while detecting switch states, powering up only when necessary to reduce static current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional pull-up or pull-down resistor is used for reed switch state detection, then switch state detection is achieved, but static current draw increases significantly
Solution Approach 1:
The patent applies periodic action by using a pulse train signal instead of continuous DC voltage to drive the reed switch. The pulse train has a duty cycle less than 100%, creating periodic on-off cycles that reduce average current draw while maintaining switch state detection capability. The comparator is enabled only during active pulses, further reducing power consumption during idle periods.
Solution Approach 2:
The patent implements dynamics by making the system state variable through the pulse train's duty cycle. The duty cycle can be adjusted to optimize between detection accuracy and power consumption. The system dynamically transitions between active detection mode (during pulses) and low-power sleep mode (between pulses), adapting power consumption to actual detection needs.
2Reliability
If continuous monitoring of switch state is performed, then detection reliability is improved, but power consumption increases
Solution Approach 1:
The system performs periodic monitoring using pulse train cycles instead of continuous monitoring. Each pulse provides an opportunity to sample the switch state, ensuring detection reliability while allowing the system to enter low-power states between pulses. The periodic nature maintains reliability by regularly checking for state changes without continuous power draw.
Solution Approach 2:
The system uses the reed switch's inherent latching property to maintain state information between pulses. The magnetic reed switch remains in its last detected state (open or closed) until a pulse triggers a new reading, allowing the system to 'remember' the state without continuous power or monitoring, thus reducing power consumption while maintaining reliability.
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
This approach significantly reduces average current draw, extending battery life by minimizing power consumption while maintaining effective switch state detection, as demonstrated by increasing battery life from 5.3 years to 7.3 years in a specific configuration.
Implementation Method 1
Magnetic reed switches or the like are typically normally-open switches that are held in the closed position when a magnet is in close proximity
Data Source
AI summary
A switch sensor for sensing a state of a switch including a programmable memory, pulse generation circuitry, and comparator circuitry. The memory stores a state value indicative of a detected state of the switch. The pulse generation circuitry provides a pulse-train voltage signal to a first end of the switch, in which the pulse-train voltage signal is toggled between an active state for switch state detection and an inactive state for conserving power. A second terminal of the switch is coupled through resistive circuitry to a supply voltage node and may be coupled to an input terminal of the sensor. The comparator circuitry compares a state of the input terminal with the state value when the pulse-train voltage signal is in the active state for providing a state change signal indicative thereof.