Detailed explanation of the design principle and imitation development plan of blood glucose meter

This article mainly discusses the circuit principle design and application analysis of the blood glucose meter based on the C8051F series single-chip microcomputer, and also provides a complete solution for imitation development, debugging and production.
Blood glucose measurement usually adopts the three-electrode system in electrochemical analysis. The three-electrode system is relative to the traditional two-electrode system, including the working electrode (WE), the reference electrode (RE) and the counter electrode (CE). The reference electrode is used to fix the zero point. The current flows through the working electrode and the counter electrode. The working electrode and the reference electrode form a system that is not or basically less energized. The electrode potential of the working electrode is measured by using the stability of the reference electrode potential. The working electrode and the auxiliary electrode form a energized system to measure the current passing through the working electrode. The three-electrode measurement system is used to simultaneously study the relationship between the point position and current of the working electrode. As shown in Figure 1.

Figure 1 Three-electrode working principle Solution
description
The blood glucose meter provides multiple operation modes to adapt to different applications. In addition, it provides free switching and automatic conversion of three common measurement units: mmol/L, mg/dl, and g/l. The conversion relationship between the three units is as follows:
1mmol/L=18 mg/dL 1mmol/L=0.18 g/L 1 mg/dL=0.01 g/L
In response to the different requirements of different countries and regions, the blood glucose meter can use any of the above units to display the measurement results. The conversion method is achieved by using a special code correction bar.
(1) Full utilization of microcontroller and internal hardware resources. The Silicon labs C8051F410 microcontroller integrates a wealth of peripheral analog devices, allowing users to fully utilize its rich hardware resources. The logic function diagram of the C8051F410 microcontroller is shown in Figure 2. The 12-bit A/D converter is used for small signal measurement. The small signal current is finally converted into voltage through the current sampling circuit and sampled by the A/D. Then the concentration is calculated by the established conversion program and displayed on the LCD panel. The 12-bit D/A converter can output an accurate and stable reference voltage for the three-electrode electrochemical measurement process. Since the output of the D/A can be changed arbitrarily by programming, the voltage difference between the reference voltage and the working voltage can be easily changed by changing the D/A value. The voltage difference can be stabilized with 12-bit accuracy, effectively improving the measurement accuracy. Figure 2 C8051F410 logic function diagram The temperature sensor is used to collect temperature signals for temperature compensation [4]. Because blood glucose reagents will have measurement deviations when the temperature is too high or too low, the ambient temperature is collected by the temperature sensor during the measurement process. This parameter can be used as temperature compensation when it is outside the temperature range required by the reagent. The internal 32/16kB Flash memory can be used to store measurement data. The 2kB integrated RAM is used as a buffer for measurement data. The blood glucose meter needs to record each measurement data and date in a non-volatile storage medium, which usually uses Flash memory. However, Flash memory generally has the problem of slow rewriting speed. Therefore, this 2kB RAM is used as a buffer to record data when there is power. The data is written to Flash each time the blood glucose meter is turned off, which indirectly improves the measurement efficiency of the blood glucose meter. (2) The power supply design uses two ordinary alkaline AAA batteries, and uses RT9701 and RT9266 to form a high-efficiency boost circuit to boost the voltage to 3.3V as the power supply for the entire blood glucose meter. In the power supply circuit structure of the entire instrument, a power switch circuit is designed. When the instrument is turned off, except for the MCU and real-time clock, which can be directly powered by the battery, the power supply of other circuits is completely cut off. Then the MCU and real-time clock enter the sleep or power saving state, which can greatly save the standby power consumption and extend the battery life. The MCU wake-up is realized through interruption. When the switch button is pressed, a key interrupt is generated, thereby waking up the MCU and connecting the power to other circuits, and the blood glucose meter enters the working state again. (3) Real-time clock design uses the s-3530A real-time clock chip [5]. The real-time clock has the characteristics of high precision and low power consumption. The working crystal frequency is 32K, and it is equipped with a power-saving mode. When the blood glucose meter is not working, it can enter the power-saving mode to save battery power. It uses the I2C bus to connect to the single-chip microcomputer, which effectively saves the single-chip microcomputer I/O port line. It automatically calculates leap years and represents the year, month, day and time data in BCD code format, which provides great convenience for MCU reading and writing. (4) Different user mode design. The end customer only needs to perform blood glucose testing and test history records, while the debugger needs to know the measured current value to detect the quality of the instrument. Therefore, this solution specially designs two operation modes for the end user and the debugger in the production process. Only a special test strip is needed to put the instrument into super user mode. This mode provides a display interface for the test current. In this interface, the debugger can use a standard resistor instead of a reagent to test the performance of the instrument. The general end user can only use it in the normal user mode. In this way, the production test and final sales of the instrument can use the same program, which brings great convenience to production and also brings convenience to the maintenance of the product. (5) Code correction of blood glucose meter. The blood glucose meter needs to be calibrated every time a batch of reagents is replaced. The so-called code calibration is actually to input a new set of fitting curve parameters into the blood glucose meter. The parameters will be burned in advance on the code calibration strip. The calibration code strip is shown in Figure 3. The characteristic code is actually the integration of the fitting curve parameters into a special code form. Figure 4 is a reagent strip, which is prepared by a professional biomedical institution. Because the preparation of each batch of reagent strips cannot be consistent, the fitting curve parameters are different each time. The parameters are provided by the institution and the corresponding calibration code strip is burned and delivered to the end user with the reagent. Every time the user purchases a new batch of reagents, the parameters of the blood glucose meter must be modified through the code calibration strip. The design of the code calibration strip uses the same interface as the reagent strip, so you only need to directly insert it into the detection port of the blood glucose meter like using a reagent strip, and you can easily input the new parameters into the blood glucose meter.

Figure 4 Reagent
(6) Based on the requirements of the previous point, the port of the blood glucose meter must be able to correctly read both the reagent strip and the calibration code strip, so the port is a composite port with two functions. Therefore, a clever circuit conversion structure is designed on the circuit to automatically determine whether it is a reagent strip or a code calibration strip according to the inserted medium and read it correctly.
(7) Design of special code calibration strip. Since this solution designs functions such as automatic unit conversion, general user mode and super user mode, the implementation of these functions depends on the special code calibration strip. The principle is to select several special codes, burn them into the code calibration strip, and use the blood glucose meter to automatically read the code calibration strip to set the parameter function. When the code is read, first determine whether it is a special code. If it is, perform the corresponding operation, otherwise enter the new parameter setting, as shown in Figure 7. Special codes include the following contents: code for converting units, code for switching working modes, code for clearing memory, etc.

Circuit implementation and human-machine interface
The circuit structure of the blood glucose meter is shown in Figure 5. The blood glucose meter uses a customized PDM1621-893 LCD module as the human-machine interface. This module can realize multiple displays such as real-time clock, battery power, measurement unit, alarm signal, code prompt, etc. In addition, combined with the programming of the three-digit seven-segment digital display, it can provide as rich prompt information as possible in multiple working modes. The LCD panel structure is shown in Figure 6. The operation process of the entire blood glucose meter is shown in Figure 7. Figure 5 Circuit structure

Figure 6 LCD panel structure diagram Figure 7 Program flow Blood glucose meter is a commonly used medical electronic instrument in clinical medicine, which mainly performs clinical diagnosis by measuring the blood glucose concentration in the blood. Century Core has many years of service experience in the field of imitation development and maintenance of various medical electronic instruments and high-end expensive medical equipment. It can provide a full set of technical services such as replacement and maintenance of medical equipment circuit boards, troubleshooting, circuit board replication, prototype cloning, debugging and production. At the same time, it can also provide the extraction and transfer of a full set of technical data of many medical electronic equipment such as blood glucose meters according to customer needs, assist product developers and users in repair, maintenance and improvement and upgrading, or assist engineers in product reference design.