Micropower Voltage-Independent Capacitance Measuring Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional capacitance measurement methods require expensive and power-consuming analog front-end circuitry, are sensitive to voltage and temperature variations, and struggle with precise measurement of small capacitance values, especially in solar cell-powered systems.
Innovation Solution
A low-power capacitance measuring circuit using a microcontroller and a variable frequency oscillator that generates time-varying signals proportional to unknown and reference capacitances, allowing for precise measurement without analog-to-digital conversion and accounting for stray capacitance, with optional voltage and temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Wheatstone Bridge configuration is used for capacitance measurement, then measurement capability is achieved, but power consumption is high and cost is expensive
Solution Approach 1:
The patent replaces the conventional Wheatstone Bridge analog circuit with a digital counting system using a microcontroller and timer. The analog-to-digital conversion is integrated into the microcontroller, eliminating the need for separate expensive and power-consuming analog front-end circuitry. The timer counts oscillator pulses during charge/discharge cycles, providing digital measurement that consumes less power and costs less.
Solution Approach 2:
The microcontroller serves multiple functions: it controls the switches for charge/discharge cycles, generates timing signals for the timer, processes the pulse counts, and performs the capacitance calculation. This multi-functionality consolidates what would otherwise require separate dedicated circuits, reducing overall power consumption and component cost.
2Measurement precision
If conventional Wheatstone Bridge configuration is used for capacitance measurement, then measurement capability is achieved, but circuit cost is expensive
Solution Approach 1:
The patent replaces the conventional Wheatstone Bridge analog circuit with a digital counting system using a microcontroller and timer. The analog-to-digital conversion is integrated into the microcontroller, eliminating the need for separate expensive and power-consuming analog front-end circuitry. The timer counts oscillator pulses during charge/discharge cycles, providing digital measurement that consumes less power and costs less.
Solution Approach 2:
The patent uses standard, inexpensive components such as off-the-shelf microcontrollers (e.g., MSP430), generic timers, and common switches. These readily available components are cheaper than specialized analog front-end circuits designed specifically for capacitance measurement, reducing overall system cost.
3Stability of the object's composition
If charge amplifier configuration is used for capacitance measurement, then voltage independence is achieved, but measurement precision is affected by operational amplifier imperfections
Solution Approach 1:
The patent eliminates the operational amplifier entirely by using a digital counting method. The microcontroller controls switches to charge and discharge capacitors through a known resistor, and a timer counts oscillator pulses during these cycles. The capacitance is calculated from the pulse counts and time intervals, providing measurement precision not limited by operational amplifier imperfections while maintaining voltage independence through the ratiometric measurement approach.
4Device complexity
If discharge time measurement method is used for small capacitance values, then measurement capability is reduced, but circuit simplicity is maintained
Solution Approach 1:
The patent uses a dynamic oscillator frequency that adapts to the capacitance value being measured. For small capacitances, the oscillator runs at higher frequencies, generating more pulses during the charge/discharge cycles. The timer counts these pulses, and the microcontroller calculates capacitance based on the pulse counts and known time intervals. This dynamic approach maintains circuit simplicity while extending measurement capability to very small capacitance values.
Solution Approach 2:
The system uses feedback through the oscillator timing mechanism. The oscillator frequency and the timer counting are synchronized with the charge/discharge cycles controlled by the microcontroller. This feedback mechanism ensures that the measurement process adapts to the actual capacitance value, providing accurate measurements across a wide range including very small capacitances while maintaining a simple circuit architecture.
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 accurate, low-power, and cost-effective measurement of small capacitance values, reducing sensitivity to voltage and temperature variations, and improving resolution down to a few picoFarads, while minimizing current consumption.
Implementation Method 1
A low-power capacitance measuring circuit using a microcontroller and a variable frequency oscillator that generates time-varying signals proportional to unknown and reference capacitances
Data Source
AI summary
A circuit for measuring an unknown capacitance includes a reference capacitor having a known capacitance, an oscillator timing circuit, a variable frequency oscillator and a microcontroller. The oscillator timing circuit includes switches which selectively couple the unknown capacitance and the reference capacitor to the oscillator timing circuit. The variable frequency oscillator generates time varying signals which vary in frequency proportionally to the unknown capacitance and reference capacitor selectively coupled to the oscillator timing circuit. The microcontroller receives the time varying signals from the oscillator, and compares the periods of the time varying signals to determine the value of the unknown capacitance.