Audio Port Ion-Selective Probe Interface with Auto-Calibration
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Solution Overview
Problem
Existing mobile device interface systems struggle to accurately read ion-selective probes that produce small DC voltages over large impedances, such as pH meters and other ion concentration sensors, due to limitations in bias current and noise rejection, leading to low precision and accuracy in measurements.
Innovation Solution
The system employs an instrumentation amplifier with low bias current and high input impedance, combined with a chopper circuit and precision rectifiers to convert DC signals into AC, and uses voltage-controlled amplifiers to adjust gain and offset, ensuring positive output and maximizing resolution through software calibration of the computing device's audio port.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a standard audio input is used to read probe signals, then the device complexity is reduced, but the measurement precision deteriorates due to high bias current and low input impedance
Solution Approach 1:
The patent introduces an intermediary circuit between the probe and the audio input that includes an instrumentation amplifier with very low bias current (picoamp to femtoamp range) and very high input impedance. This intermediary buffer amplifier converts the high-impedance probe signal into a low-impedance signal suitable for audio input while maintaining measurement precision, effectively mediating between the incompatible impedance requirements of the probe and the audio interface.
2Device complexity
If the gain of the instrumentation amplifier is fixed, then the device complexity is reduced, but the adaptability deteriorates when measuring different ion concentration ranges
Solution Approach 1:
The patent implements a variable gain amplifier stage following the fixed-gain instrumentation amplifier. This variable gain stage allows the system to adapt to different ion concentration ranges by dynamically adjusting the amplification factor, enabling the interface to handle both very low and very high concentration measurements with a single device while maintaining relatively simple fixed-gain instrumentation amplifier circuitry.
3Device complexity
If the output voltage is not transformed, then the device complexity is reduced, but the measurement precision deteriorates when the signal range does not match the microphone dynamic range
Solution Approach 1:
The patent employs a variable gain amplifier and offset adjustment circuitry that dynamically changes the voltage parameters of the probe signal to match the dynamic range of the microphone input. By adjusting the gain and offset parameters, the system maximizes the utilization of the audio interface's dynamic range, ensuring optimal resolution and precision across different measurement conditions without requiring complex analog-to-digital conversion circuitry.
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 enables precise and accurate readings from ion-selective probes by maximizing the dynamic range of the microphone input, preventing signal clipping and providing scientific-grade measurements across various ion concentration sensors.
Implementation Method 1
we use a chopper circuit to convert the DC signal to a waveform whose amplitude, proportional to root mean square (RMS) is linearly proportional to the linearly transformed probe voltage
Implementation Method 2
using a precision rectifier for each speaker wire to end up with a DC output proportional to the amplitude of the speaker wire signals
Implementation Method 3
the probe is connected to an instrumentation amplifier of the interface with a very low bias current and very high input impedance. This is necessary in order to get a voltage reading on probes that may only produce currents in the picoamp and femtoamp order of magnitude
Implementation Method 4
The first voltage controlled amplifier controls the offset voltage while the second controls gain on the signal from the instrumentation amplifier
Data Source
AI summary
A system and method for an interface reading ion-selective probes through a device with an audio input with stereo output and mono microphone inline input. Using this interface, multiple probes with different voltage ranges can be handled using one output speaker line to control offset while the other controls gain on the signal from the probe. The output from the interface is read and interpreted via the microphone bidirectional input of the device with the audio port. Furthermore, by reading the microphone input, the device with the audio port auto-calibrate and auto-range fear maximum resolution for the microphone's given dynamic range by adjusting the output fix the two speaker lines, the offset and gain.