Soil Moisture Sensor Controller Using Capacitance Oscillator
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Solution Overview
Problem
Capacitance-based moisture sensors in irrigation systems are unreliable due to variations in temperature and supply voltage, and they fail to accurately measure soil moisture levels across different zones with varying soil types and sunlight exposure.
Innovation Solution
An integrated moisture sensor and controller device is placed in the soil, featuring a probe that forms a capacitor, a variable frequency oscillator, and a reference oscillator, which compares frequencies to determine soil moisture levels and control irrigation valve actuation, thereby preventing over-watering by interrupting power to the valve when moisture exceeds a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single moisture sensor is used for all zones in an irrigation system, then the controller structure is simplified, but the measurement precision deteriorates because different zones have different soil types and weather conditions
Solution Approach 1:
The patent divides the irrigation system into multiple independent zones, each with its own moisture sensor and control circuitry. The controller is segmented to handle individual zone measurements and control decisions separately, allowing each zone to be monitored and controlled independently based on its specific soil type and weather conditions.
2Measurement precision
If capacitance-based moisture sensors are used to measure soil moisture levels, then the measurement capability is provided, but the reliability deteriorates due to variations in temperature and supply voltage
Solution Approach 1:
The patent incorporates temperature sensors and voltage monitoring circuitry that provide feedback to the control system. The controller uses this feedback information to compensate for temperature variations and supply voltage fluctuations, adjusting the capacitance-based moisture measurements to maintain accurate and reliable operation under varying environmental conditions.
3Device complexity
If the controller uses a single moisture sensor for all zones, then the device complexity is reduced, but the adaptability deteriorates when different zones have different soil types or weather conditions
Solution Approach 1:
The system is divided into independent zone units, each with its own sensor and control logic, enabling zone-specific adaptation to different soil types and weather conditions while maintaining a modular architecture that doesn't excessively increase overall system complexity.
Solution Approach 2:
The controller is designed with universal capabilities to handle multiple zones with different characteristics. Each zone can be independently configured for its specific soil type and environmental conditions, allowing the same controller hardware to adaptively manage diverse irrigation requirements across different zones.
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 solution provides accurate and zone-specific moisture monitoring, preventing over-watering and ensuring each zone receives the right amount of water without requiring frequent reprogramming of the irrigation controller, while being resistant to temperature and voltage variations.
Implementation Method 1
a probe forming a capacitor and adapted to be positioned within soil; a controller coupled to the probe, the controller comprising a variable frequency oscillator, the frequency of the variable frequency oscillator varies as a function of a capacitance of the probe, the capacitance varies as a function of a moisture content of the soil
Implementation Method 2
a variable frequency oscillator, the frequency of the variable frequency oscillator varies as a function of a capacitance of the probe
Implementation Method 3
a reference oscillator; and a circuit for comparing the frequency of the variable frequency oscillator to a frequency of the reference oscillator
Data Source
AI summary
Moisture sensor devices and methods associated with operation of the moisture sensor devices are disclosed herein. One embodiment includes a moisture sensor and controller device adapted to be placed in soil comprising a switch adapted to be coupled to a power control line of an irrigation controller, the power control line for sending an activating power signal to an irrigation valve; a control circuit coupled to the switch; and a sensor circuit coupled to the control circuit and adapted to provide a signal to the control circuit, the signal corresponding to a moisture level of the soil; wherein the control circuit is adapted to control the switch to interrupt the activating power signal based on the signal from the sensor circuit; wherein the switch and the control circuit are both external to the irrigation controller.