A glucometer is a vital tool utilized in the medical industry, specifically for monitoring and managing diabetes. Ensuring the accuracy of measurement results is crucial for establishing trust with clients. Therefore, it is imperative to highlight the device’s professional and reliable attributes.
The underlying principle of a blood glucose meter involves the interaction of blood samples with electrodes present on the test strip. This interaction triggers the catalytic oxidation reaction of glucose by glucose oxidase, leading to the release of electrons and the generation of electrical signals. The measuring device subsequently calculates the intensity of the current signal to determine the corresponding glucose concentration.
In this comprehensive article, TechSpark will delve into the design and application analysis of the circuit principle utilized in the glucometer. Our focus will be on leveraging the C8051F series single-chip microcomputer, renowned for its high-performance capabilities. Additionally, we will provide a comprehensive solution encompassing development, debugging, and production to facilitate seamless imitation of the glucometer.
Glucometer Three Electrode System
In the glucometer circuit, a three-electrode system comprising the working electrode (WE), reference electrode (RE), and counter electrode (CE) is utilized. This configuration offers significant advantages over the two-electrode system, primarily due to the inclusion of the counter electrode.
The reference electrode plays a critical role in establishing a precise and fixed potential zero point. As current traverses through the working electrode and reference electrode, a distinct “cut-off” region is formed between them. The potential of the working electrode is then measured by leveraging the stability of the reference electrode’s potential. Essentially, the reference electrode provides a reliable and stable potential reference, enabling the accurate measurement of the working electrode’s potential without being affected by external factors. It’s important to note that the energized region is formed between the working electrode and the counter electrode, facilitating the calculation of the current passing through the working electrode.
With the implementation of this three-electrode system, we can simultaneously investigate the relationship between the position of the working electrode and the corresponding current. As shown in the figure below:
Customized Blood Glucose Meter Circuit Scheme
To cater to diverse application scenarios, the glucometer employed in our project offers a range of operational modes. Furthermore, it facilitates seamless conversion between three commonly used measurement units: mmol/L, mg/dL, and g/L. Achieving this conversion requires the utilization of specialized code correction strips and a comprehensive understanding of the interrelationships among the three units:
- 1 mmol/L = 18 mg/dL
- 1 mmol/L = 0.18 g/L
- 1 mg/dL = 0.01 g/L
By incorporating this functionality, the blood glucose meter empowers users with the flexibility to select their preferred measurement unit, enhancing convenience and facilitating accurate interpretation of glucose levels.
Microcontroller and Hardware
The C8051F410 microcontroller, developed and manufactured by Silicon Labs, is a highly regarded single-chip microcomputer in the C8051F series known for its exceptional performance, low power consumption, and extensive integration capabilities.
Utilizing the C8051 core architecture and based on the MCS-51 instruction set, the C8051F410 microcontroller employs a 12-bit analog-to-digital converter (ADC) to measure small signals. These signals, in the form of small currents, are converted into voltages through a current sampling circuit and subsequently sampled by the ADC. The sampled voltage is then processed using a predefined conversion program, and the calculated results are displayed on the liquid crystal panel, representing the corresponding concentration information.
Additionally, the C8051F410 microcontroller features a 12-bit digital-to-analog converter (DAC), which allows for the precise and stable generation of reference voltages for electrochemical measurements involving three electrodes. By programmatically adjusting the output value of the DAC, the voltage difference between the reference voltage and the working voltage can be easily modified. The 12-bit resolution of the DAC ensures the stability of the voltage difference, thereby significantly enhancing measurement accuracy.
To account for the influence of temperature on measurement accuracy, a temperature sensor is incorporated. The temperature sensor captures the ambient temperature and facilitates temperature compensation. Given that measurement errors may arise when the temperature deviates from the optimal range for the blood glucose reagent, the collected temperature parameter is utilized for temperature compensation, effectively correcting the measurement results.
With regards to data storage, the C8051F410 microcontroller integrates 32/16kB of Flash memory to accommodate measurement data. To ensure reliable and non-volatile data storage, each measurement’s data and corresponding date are recorded in the Flash memory. However, it should be noted that Flash memory is known for its relatively slow rewriting speed. To address this limitation, the 2kB integrated RAM serves as a buffer for measurement data. During periods of power availability, the RAM is employed to store data, while the actual writing of the data into the Flash memory occurs when the glucometer is powered off. This approach indirectly improves measurement efficiency.
Power Supply Design
This project incorporates a power supply design based on two standard alkaline AAA batteries, which serve as the primary power source. To ensure a stable current for the blood sugar monitoring devices, a highly efficient boost circuit comprising of RT9701 and RT9266 is utilized to elevate the power supply voltage to 3.3V. This voltage increase facilitates reliable operation of the glucometer.
To maximize the device’s standby time, a well-conceived circuit power supply structure has been devised. When the device is powered off, only the MCU (Microcontroller Unit) and real-time clock retain direct battery power. In contrast, power to the remaining circuits is completely cut off. To activate the MCU and restore the blood glucose meter to its working state, a simple press of the switch button is sufficient. This action triggers a button interruption within the circuit, causing the glucometer to resume its operations.
When incorporating a real-time clock into the design, the s-3530A chip is utilized. This particular chip stands out for its high precision and low power consumption attributes. Operating at a crystal oscillator frequency of 32K, it ensures accurate time and date information while featuring a power-saving mode. The connection to the single-chip microcomputer is established through the I2C bus, streamlining the integration process by reducing the required number of I/O ports. Notably, the S-3530A real-time clock chip automatically handles leap year calculations and adopts the BCD code format for representing year, month, day, and time data. This representation method significantly enhances the microcontroller’s ease of data manipulation, resulting in a more streamlined and convenient operation.
Two-layer Operation Mode Design
Different users have distinct priorities. End customers primarily focus on blood glucose testing and historical records, while debuggers require knowledge of the measured current value to ensure instrument quality. Therefore, glucometer circuit design must cater to the needs of both user groups.
For end customers, the design restricts them from performing blood glucose tests and recording data solely in normal user mode. This restriction mitigates the risk of inaccurate test results due to unauthorized debugging. Consequently, it enhances the convenience of after-sales customer service and maintenance support.
For debuggers involved in the production process, a super user mode is provided to facilitate quality inspections. By utilizing a specialized test strip, debuggers can access the instrument’s super user mode. Within this mode, debuggers gain visibility into the precise test current value and can employ standard resistances as substitutes for reagents to evaluate instrument performance.
Code Calibration of Blood Glucose Meter
The process of code correction is essential when introducing a new production batch for the glucometer. It involves inputting the newly determined curve parameters into the device, which are pre-programmed into the code correction strip. The feature code represents the integrated form of these curve parameters in a special code format.
Reagent strips, vital components of the glucometer, are meticulously prepared by professional medical institutions. Due to the inherent variability in each reagent batch, the corresponding curve parameters will differ accordingly.
The institution responsible for providing the parameters supplies them along with the reagent batches. The corresponding calibration code strips are programmed with the specific parameters and delivered to end users. Each time a new batch of reagents is purchased, the blood glucose meter’s parameters must be adjusted using the code correction strip. Designed with a compatible interface to the reagent strip, the code correction strip can be easily inserted into the device’s test port, facilitating the seamless input of new parameters.
In accordance with the aforementioned specifications, the glucometer’s port is designed to fulfill two key functions: accurately reading the reagent strip and retrieving data from the calibration code strip. To achieve this, an ingenious circuit conversion structure has been implemented in the overall glucose meter design. This circuitry intelligently identifies the type of medium being inserted, whether it is a reagent strip or a code correction strip, and performs the reading operation accordingly, ensuring precise and reliable results. This well-thought-out design transforms the port into a versatile composite interface capable of seamlessly accommodating and effectively processing different types of media for optimal performance.
Glucometer Circuit Diagram and UI
The circuit logic structure diagram and LCD panel structure diagram of the blood sugar monitor project are illustrated below. It incorporate a customized LCD module, PDM1621-893, as its human-machine interface. This LCD module is capable of displaying various essential information for measurement purposes, including real-time clock, battery power, measurement unit, alarm signals, code prompts, and more. Furthermore, by leveraging the programming of the three-digit seven-segment digital display, the meter can provide comprehensive prompt information in multiple working modes.
As a medical electronic device widely used in clinical medicine, the glucometer emphasizes user-friendly operation to enhance its practicality. By following the operation process depicted in the figure below, users can accurately perform clinical diagnosis of blood glucose concentration through two available switching modes.