Colorimetric-potential combined automatic titration device based on single-chip microcomputer and application of colorimetric-potential combined automatic titration device

Abstract

The invention relates to a chemical analysis instrument, and particularly discloses a colorimetric-potentiometric combined automatic titration device based on a single chip microcomputer and application of the colorimetric-potentiometric combined automatic titration device. The device comprises a control module, a potential detection module, a color detection module, a fluid driving module, a signal conversion module and a power supply module. The core of the device is that a single-chip microcomputer is taken as a control center, potential signals of a pH composite electrode and light intensity signals of an AS7341 sensor are synchronously acquired, a real-time dynamic linkage titration curve is generated through double data sources, visualization of potential and color mutation is realized, and faults of a single sensor are effectively identified. According to the device, the end point judgment reliability is improved through double-signal cross validation, complex sample analysis can be dealt with, double-dimensional data are synchronously obtained through single titration, the experiment efficiency is improved, hardware modular design is convenient to expand, and the device is suitable for chemical experiment teaching and scientific research scenes.

Description

Technical Field

[0001] This invention relates to a chemical analysis instrument, and more particularly to a microcontroller-based automatic colorimetric-potential titration device. Background Technology

[0002] In the field of analytical chemistry, titration analysis is a classic and core quantitative analytical method, widely used in areas such as the determination of substance composition. Instrumental titration technology, with its advantages of high automation and good data repeatability, has become the mainstream development direction of titration analysis. With the development of science and technology and the advancement of educational informatization, traditional titration instruments can no longer meet modern needs: on the one hand, in undergraduate analytical experimental teaching, commercially available instruments are often "black boxes," making it difficult for students to intuitively understand the internal structure and signal processing principles of the instruments, which is not conducive to the cultivation of interdisciplinary literacy; on the other hand, in scientific research scenarios, existing titration devices mostly adopt a single detection mode (such as potentiometric titration only or photometric titration only), which has problems such as the endpoint determination being easily interfered with and a narrow range of applicable samples.

[0003] As a highly integrated microcomputer system, the microcontroller boasts advantages such as low cost, small size, low power consumption, and programmable control, making it a core component of embedded control systems and widely used in industrial automation, intelligent detection, and other fields. Combining microcontroller technology with titration analysis can achieve precise control of the titration process and digital data acquisition. However, current related devices mostly focus on single signal detection, failing to achieve multi-signal collaborative monitoring and cross-validation, and there is still room for improvement in signal noise reduction and data visualization.

[0004] The existing technology has the following shortcomings: 1) High equipment cost: the price of commercially available multifunctional titrators generally exceeds 10,000 yuan, which is not conducive to the mass production and equipment of university laboratories; 2) Limited functionality: most devices only support a single detection mode, and the endpoint determination error is large when facing samples with dark color or complex ionic strength; 3) Poor teaching adaptability: the "black box" design makes it impossible for students to participate in device debugging and principle exploration; 4) Limited data dimension: a single titration can only obtain one detection signal, and multiple experiments are required to verify the results, resulting in low experimental efficiency. Summary of the Invention

[0005] To address the problems of high cost, limited functionality, poor adaptability to teaching, and insufficient data dimensions in existing titration devices, this invention provides a microcontroller-based automatic colorimetric-potential titration device. It generates dynamic colorimetric-potential linkage titration curves in real time by integrating potential detection and colorimetric detection modes, enabling visualization of potential and color abrupt changes. Simultaneously, synchronous acquisition and cross-validation of dual signals improve the reliability of endpoint determination. Modular hardware design reduces costs and adapts to teaching needs; multi-dimensional data acquisition enhances experimental efficiency.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a microcontroller-based automatic titration device for colorimetry and potentiometric combined titration, comprising a control module, a potential detection module, a colorimetric detection module, a fluid drive module, a signal conversion module, a communication module, and a power supply module, wherein each module works in concert to achieve automatic titration and multi-signal acquisition.

[0007] The specific structure and connection relationship of each module of this invention are as follows:

[0008] (1) Control Module: The STM32F401CCU6 microcontroller is used as the central processing unit. This microcontroller is a 32-bit high-performance microcontroller with rich peripheral interfaces, which can realize precise control and data processing of each module. Its core functions include: receiving and parsing the host computer instructions, controlling the start, stop and speed adjustment of the peristaltic pump, synchronously acquiring potential and spectral signals, processing data and generating titration curves, and feeding back data through the communication module.

[0009] (2) Potential detection module: It consists of a pH composite electrode and an INA828 instrumentation amplifier. The pH composite electrode is used to sense the change in hydrogen ion activity in the solution during titration and outputs a weak potential signal at the millivolt level. Since the electrode output impedance is high, the signal needs to be conditioned by the INA828 instrumentation amplifier. This amplifier has the characteristics of high input impedance, low noise and high common-mode rejection ratio, which can effectively extract the microvolt potential signal and amplify it to the range suitable for analog-to-digital conversion.

[0010] (3) Signal Conversion Module: The ADS8685 16-bit analog-to-digital converter is used to convert the analog voltage signal output by the INA828 into a digital signal. Compared with the 12-bit ADC built into the microcontroller, the 16-bit resolution can improve performance in many aspects, especially in situations where high accuracy and stability are required. The sampling rate of 500kSPS can meet the real-time signal acquisition requirements. The ADS8685 communicates with the STM32F401CCU6 microcontroller through the SPI interface to achieve high-speed data transmission.

[0011] (4) Colorimetric detection module: Employs an AS7341 visible spectrum sensor, via I... 2 The sensor connects to a microcontroller via a C-bus and is used to monitor color changes in the solution during titration. It integrates eight spectral channels for high-precision color measurement, a six-parallel ADC architecture supports high sampling rates, and a scintillation detection engine suppresses ambient light interference, ensuring the stability of color signal acquisition.

[0012] (5) Fluid drive module: It consists of a miniature peristaltic pump and a TMC2208 driver board. The miniature peristaltic pump is driven by a stepper motor, which has the characteristics of being pollution-free and having a stable flow rate, making it suitable for the precise delivery of titrants; the TMC2208 driver board receives the stepping pulses and direction signals output by the microcontroller, and precisely drives the stepper motor of the peristaltic pump. The TMC2208 can also be configured with detailed motor parameters through the UART interface.

[0013] • (6) Communication module: The CP2102 USB to UART converter forms the programming and debugging bridge of the system, connecting the USART1 interface (PA9-TX, PA10-RX) of STM32F401CCU6 to the computer USB port, which facilitates program burning and data monitoring.

[0014] • (7) Power supply module: The TPS61089 synchronous boost converter is used to provide a stable power supply for the INA828 instrumentation amplifier.

[0015] The signal flow of this invention is as follows: pH composite electrode → INA828 instrumentation amplifier → ADS8685 analog-to-digital converter → STM32F401CCU6 microcontroller; AS7341 sensor → STM32F401CCU6 microcontroller; STM32F401CCU6 microcontroller → TMC2208 driver board → micro peristaltic pump; STM32F401CCU6 microcontroller → CP2102 converter → host computer.

[0016] Therefore, the present invention can achieve the following beneficial effects:

[0017] (1) Significantly improved reliability of endpoint determination: This device uses two different physical signals to perform dual independent verification of the titration endpoint. When the two signals show a significant jump near the same position of the titrant volume, this provides strong mutual confirmation, reduces the endpoint misjudgment error caused by interference that may be encountered by a single method, effectively avoids the subjective judgment error of visual indicator color change, and makes the results more objective and highly confident.

[0018] (2) The scope of application has been greatly expanded: the dual-signal redundancy design enables the device to handle complex sample analysis. For example, the titration of dark solution can rely on the potential signal, and the sample with large fluctuations in ionic strength can rely on the colorimetric signal, which solves the problem that traditional single-mode devices cannot accurately detect special samples.

[0019] (3) Dual improvement in experimental efficiency and data dimension: Each titration experiment can simultaneously and completely capture the changes in potential and solution color intensity with the amount of titrant added during the entire titration process, which greatly saves valuable sample consumption, reagent costs, instrument occupation time and operator man-hours, and significantly improves the throughput and operating efficiency of the laboratory.

[0020] (4) Excellent teaching adaptability: The modular hardware design facilitates students' assembly and debugging, and the transparent signal processing flow can help students understand the instrument principle.

[0021] The core technical points of this invention include:

[0022] (1) Low noise signal processing technology: The INA828 instrumentation amplifier is adapted to the high impedance pH electrode and combined with the ADS8685 16-bit ADC to achieve low noise extraction of microvolt potential signals.

[0023] (2) Dual-signal linkage endpoint determination algorithm: The potential signal and the spectral light intensity signal are monitored simultaneously, and the titration endpoint is determined by a dual-condition jump, which improves the reliability of the results.

[0024] (3) Software and hardware co-control scheme: sensor driver encapsulation based on Python environment, GUI interface design using pyQt, including "potential-volume" curve, "light intensity-volume" curve and "channel-light intensity-volume" three-dimensional surface, as well as peristaltic pump precision fluid delivery control logic with adaptive PID speed regulation.

[0025] (4) Modular hardware integration solution: hierarchical power supply and standardized interface connection method for power supply system and signal acquisition system to ensure system stability and scalability.

[0026] Alternative solutions

[0027] 1. Component replacement

[0028] (1) Central processing unit: embedded controllers with I2C / SPI interfaces such as Raspberry Pi 4B and Arduino Mega can replace STM32F401CCU6, but the corresponding driver needs to be adapted.

[0029] (2) Instrumentation amplifiers: INA128, AD8421 and other high-precision instrumentation amplifiers can replace INA828. The gain and bias voltage parameters need to be recalibrated.

[0030] (3) Analog-to-digital converter: ADS1256, MAX11200 and other 16-bit or higher resolution ADCs can replace ADS8688, and the SPI communication protocol and sampling rate configuration can be adjusted.

[0031] (4) Spectral sensor: TCS34725, AS7262 and other multi-channel color sensors can replace AS7341 and are compatible with spectral channel data processing algorithms.

[0032] 2. Structural and methodological substitution

[0033] (1) Fluid delivery device: The syringe pump can replace the peristaltic pump. The syringe piston is driven by a stepper motor to achieve high-precision fluid output. The drive control logic needs to be modified.

[0034] (2) Signal transmission interface: Serial communication can replace the I2C / SPI interface to connect the sensor, but the hardware wiring and data transmission protocol need to be adjusted.

[0035] (3) Endpoint determination method: A conductivity sensor can be added as a third monitoring signal, or only the potential method / spectral method single monitoring mode can be retained to simplify the data processing algorithm. Attached Figure Description

[0036] Figure 1 This is a diagram showing the connection relationships between various hardware components;

[0037] Figure 2 It is the overall software architecture diagram;

[0038] Figure 3 This is a schematic diagram of the software interface;

[0039] Figure 4 This is a flowchart of the filtering algorithm. Detailed Implementation

[0040] 1. Operating principle of the device

[0041] The precision measurement signal chain begins at the pH composite electrode, which generates a weak millivolt-level potential difference signal that is directly input to the differential input of the INA828 instrumentation amplifier. The INA828, with its high input impedance and low noise characteristics, processes the signal. The conditioned signal is then sent to the ADS8685 analog-to-digital converter, a 16-bit high-precision ADC that converts the analog voltage into a digital value via an SPI interface for the STM32 to read. Simultaneously, the AS7341 visible spectrum sensor connects via I... 2 The C-bus connects to the main controller and is used to supplement optical measurements.

[0042] The fluid drive and control section consists of a miniature peristaltic pump and its drive system. The STM32 microcontroller generates stepping pulses and direction signals to control the TMC2208 driver board, thereby precisely driving the stepper motor of the peristaltic pump. The TMC2208 can also be configured with detailed motor parameters via a UART interface.

[0043] In the auxiliary circuit, the TPS61089 synchronous boost converter provides efficient and stable power to the INA instrumentation amplifier system. The CP2102 USB to UART converter forms a bridge for system programming and debugging, connecting the STM32's USART1 (PA9-TX, PA10-RX) to the computer's USB port for convenient program burning and data monitoring.

[0044] To ensure system accuracy, the grounding (AGND) of the analog section (INA828, ADS8685) and the grounding (DGND) of the digital section (STM32, TMC2208) should be connected at a single point, and decoupling capacitors should be placed near the power supply pins of each chip to minimize the interference of digital noise on sensitive analog signals.

[0045] 2. Software Configuration (Host Computer Environment)

[0046] To develop a host computer Python program for a precision measurement system based on the STM32F401CCU6, the first step is to configure a Python 3.8+ environment and install the pyserial, matplotlib, and numpy libraries. The core program establishes stable serial communication with the slave device through a custom communication protocol and employs a multi-threaded architecture to achieve parallel processing of data transmission and control: the main thread handles user interaction (such as manually requesting pH data, controlling the peristaltic pump's runtime, or displaying real-time curves), while an independent thread continuously listens for and parses the sensor data (such as pH values ​​or spectral data) uploaded by the slave device. The program utilizes the struct module to accurately pack / unpack floating-point numbers, ensuring the accuracy of numerical transmission, and uses matplotlib to visualize historical pH data. To ensure system collaboration, the STM32 slave device needs to be configured with corresponding serial port parameters and implement the corresponding protocol parsing logic to respond to host computer commands and periodically upload sensor data.

[0047] 3. Experiment Implementation

[0048] Taking the titration of HCl with NaOH as an example, the specific steps are as follows:

[0049] (1) Preparation before the experiment:

[0050] ①Electrode activation: After immersing the newly opened pH composite electrode in 3 mol·L⁻¹ KCl solution for more than 24 hours, the electrode is calibrated to ensure that it can work normally.

[0051] ② Peristaltic pump calibration (performed individually for each pump): In the software interface, set the initial pulse count to 10,000 and the pulse increment step to 10,000. After each pulse phase, record the weighed mass m. i Immediately after determining the mass, measure the temperature of the solution and determine the density of pure water at that temperature using a table. Plot the obtained experimental data into a volume-pulse number curve; the slope is the key parameter for converting liquid volume to pulse number.

[0052] (2) Hardware assembly:

[0053] ① Circuit connection

[0054] STM32 pin Function Signal direction User Tags Connect target PA9 USART1_TX Output — CP2102 RX PA10 USART1_RX enter — CP2102 TX PB6 I2C1_SCL Two-way — AS7341 SCL PB7 I2C1_SDA Two-way — AS7341 SDA PA5 SPI1_SCK Output — ADS856x SCK PA6 SPI1_MISO enter — ADS856x SDO PA7 SPI1_MOSI Output — ADS856x SDI PB1 GPIO_Output Output CS ADS856x CS̄ PB0 GPIO_Input enter RVS ADS856x BUSȲ / RVS PB2 GPIO_Output Output RST ADS856x RST̄ PC13 GPIO_Output Output StatusLED LED (optional)

[0055] ②Electrode and sensor positioning

[0056] a. The pH electrode is inserted into the 3D-printed beaker lid with a 14 mm cap hole until the glass membrane is completely submerged in the liquid.

[0057] b. Insert the AS7341 module into the slot, and position the window at the solution surface.

[0058] c. Insert the dispensing ports of the injection pump and titration pump into the special holes and fix the position of the tubing.

[0059] ③ Electrical inspection

[0060] a. Connect the computer to the CP2102 using a USB Type-C cable.

[0061] b. Use a multimeter to measure the output of TPS61089: 9.00 ±1.00 V; INA828 power supply: 9 V.

[0062] c. Lightly touch the test button on the microcontroller and observe the two pumps rotating for 1 second to confirm that there is no jamming or leakage.

[0063] (3) Automatic titration

[0064] ① Sample injection

[0065] a. Click “Start”, and the injection pump and titration pump will draw the corresponding test solution and titrant in the forward direction until the tube is full of solution.

[0066] b. Add 2 drops of phenolphthalein to the titration beaker, set the injection volume and titrant concentration, and start the injection.

[0067] ② Titration

[0068] After sample injection, the device automatically enters titration mode, at which point it begins to generate real-time potential-volume curves, light intensity-volume curves, and a three-dimensional channel-light intensity-volume surface. After titration, the software automatically performs differentiation to find the titration jump point and calculates the concentration of the test solution, which is then displayed on the interface.

[0069] ③ Data storage

[0070] After the experiment, the data is automatically stored in an Excel format in a predetermined location on the computer, and the corresponding settings information (titration time, titrant concentration, injection volume, titration volume, and concentration of the test solution) are retained.

Claims

1. A single-chip microcomputer-based automatic colorimetric-potentiometric combined titration device, characterized by comprising: The device comprises a control module, a potential detection module, a color detection module, a fluid driving module, a signal conversion module and a power module; the control module is a single-chip microcomputer, serving as the control and calculation core of the device; the potential detection module comprises a pH electrode and an instrument amplifier, and the output end of the pH electrode is connected with the differential input end of the instrument amplifier; The signal conversion module comprises an analog-to-digital converter, the output end of the instrument amplifier is connected with the input end of the analog-to-digital converter, and the analog-to-digital converter communicates with the single-chip microcomputer through an SPI interface; the color detection module is a visible spectrum sensor, which is connected with the single-chip microcomputer through an I2C bus; the fluid driving module comprises a peristaltic pump and a driving board, and the single-chip microcomputer controls the driving board through a step pulse and a direction signal; the power module is a power converter, which supplies power for the instrument amplifier; the device further comprises a communication converter, which is connected with the single-chip microcomputer through a USART interface, and realizes communication with an upper computer.

2. The single-chip microcomputer-based combined colorimetric-potentiometric automatic titration device according to claim 1, characterized in that, The single-chip microcomputer is an STM32F401CCU6 single-chip microcomputer.

3. The single-chip microcomputer-based combined colorimetric-potentiometric automatic titration device according to claim 1, characterized in that, The instrument amplifier is an INA828 instrument amplifier, which has the characteristics of low input offset voltage of 50 μV, temperature drift of 0.5 μV / °C, noise density of 7 nV / √Hz and minimum common-mode rejection ratio of 140 dB.

4. The single-chip microcomputer-based combined colorimetric-potentiometric automatic titration device according to claim 1, characterized in that, The analog-to-digital converter is an ADS8685 analog-to-digital converter, which has a resolution of 16 bits, a sampling rate of ≥500 kSPS, supports an 8-channel integrated SAR structure and high voltage protection.

5. The single-chip microcomputer-based combined colorimetric-potentiometric automatic titration device according to claim 1, characterized in that, The visible spectrum sensor is an AS7341 sensor, which has 8 visible light channels, an integrated 6-parallel ADC architecture and a flicker detection engine.

6. The single-chip microcomputer-based combined colorimetric-potentiometric automatic titration device according to claim 1, characterized in that, The driving board is a TMC2208 driving board, which can configure motor operation parameters through a UART interface, realizes precise speed regulation and forward / reverse rotation control of the peristaltic pump.

7. The single-chip microcomputer-based combined colorimetric-potentiometric automatic titration device according to claim 1, characterized in that, The power converter is a TPS61089 converter; and the communication converter is a CP2102 converter.

8. The single-chip microcomputer-based combined colorimetric-potentiometric automatic titration device according to claim 1, characterized in that, The analog circuit part and the digital circuit part of the device adopt independent ground symbols, AGND and DGND, respectively, and AGND and DGND adopt a single-point connection mode.

9. A titration control method for the single-chip microcomputer-based combined colorimetric-potential automatic titrator according to any one of claims 1 to 8, characterized in that, The control module is programmed to perform the following steps: synchronous control, data processing, curve generation and end point determination.

10. The use of a single-chip microcomputer-based combined colorimetric-potentiometric automatic titration device according to any one of claims 1 to 8, characterized in that, The device is used for titration analysis in chemical analysis experiments, synchronously collects potential signals and light intensity signals in the titration process, generates "potential-volume" curves, "light intensity-volume" curves and "channel-light intensity-volume" three-dimensional surfaces, and realizes double verification of the titration end point.

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