Based on the MSP430 series single-chip design multifunctional blood glucose meter

Summary: this article details the design using MSP430 series single-chip microcomputer multifunctional blood glucose meter. This glucose meter not only can accurately measure blood sugar, real-time clock, also with temperature display and alarm cues, and other functions. The article describes the design principles and design of hardware and software, and finally to the design of most core and key formula.

Introduction to the current market blood glucose meter, shape structure, while the price qianqibai and precision are quite different; and it is difficult to price and accuracy.

The reason is not found a suitable microprocessor. In addition, due to screen size constraints, interface commonly used English characters appear, this gives China a patient on a certain confusion. With the development of electronic technology, microprocessor capabilities growing increasingly lower prices. There is a need to elect a powerful and inexpensive microprocessors to redesign the blood glucose meter. The system selects the MSP430 Series microprocessor makes this vision possible.

Principle of glucose meter is based on the principle of electro-biochemistry--impose a certain voltage to the enzyme reaction of blood resulting current as the blood glucose concentration in the blood increases — by design.

By accurately measuring out these weak current, and according to the current value and the relationship between blood glucose concentration, figure out the appropriate concentration. Therefore, to determine the relationship is the core of the problem. But their relationship is complex and influenced by many factors. Voltage intensity, the use of the discussion and the detection of blood volume will have an impact on it. In theory, you need all the concentration point on a large number of experiments to determine the final relationship. In practice, simply select the number of significant concentration points do a large number of experiments, and determine its current value. The points between adjacent concentration using simple linear relationship. Figure 1 summarizes the design of a certain amount of voltage between curves.

System hardware design according to blood glucose meter feature to the actual demand, combined with the MSP430 series single-chip features, using the model for the microcontroller as control MSP430F435 core, other modules have current detection, press ENTER, and power, displays, speakers and serial communication, etc.

As shown in Figure 1.

Figure 1 system composition MSP430F435 SCM SCM selection of this system has a Flash memory 16Kb MSP430F435, 512B RAM, up to 160 segment LCD drive, 8-channel/12-bit ADC and a large number of I/O ports, and so on, fully satisfy the glucose meter's functional requirements.

Figure 2 microprocessor port set main port settings as shown in Figure 2.

Which COM0 ~ COM3, S16 ~ S39, R03 ~ R33 for LCD display; Port74 and Port75 for serial communications; Port79 ~ Port81 as key inputs; Port76 and Port77 are operational amplifier and RS-232 chip provides supply voltage. Port78 connection buzzer; Port2 and Port3 Port7 for ADC input; reference voltage output; XOUT and XIN connection 32KHz Crystal, this is the system clock source. LCD display with LCD function MSP430F435, maximum support 160 segment LCD with low power consumption. This system uses a Chinese language interface, LCD display, this is the paragraph a glucose meter. This code segment LCD 96, content-rich, powerful. Greatly facilitates the use of domestic patients. Blood glucose measurement principle already know from the measurement of blood sugar is needed in the appropriate electrode voltage, imposed certain and voltage stability will directly affect the measurement results, therefore, considered from relatively stable reference voltage gain, rather than directly from the power supply. MSP430 microcontroller with A/D sampling is the voltage value is detected in the current value is minimal; therefore need to enlarge the current value and is converted to the appropriate voltage values. Used as shown in Figure 3 the circuit can achieve this requirement. The resistance R for amplification. In addition, the small amount of blood will cause deviation; therefore it is necessary to design one for the detection of blood is enough simple circuit. But this circuit can be used with the same circuit in Figure 3. It takes two such circuits can achieve blood glucose measurement.

Figure 3 amplifying circuit other modules of the system's power supply voltage of 3V, using two batteries.

One is the statue of the power supply; another piece of equipment for alternate so that the battery is still functioning. Press the key with three, are left, right and OK key; OK key is mainly used for open, shutdown, and confirm that, left to figures or options to the left, and right then with the left button instead. Since glucose meter in a large number of measurement results, it was necessary to increase the serial communication function, these results on a PC for further processing. While SCM itself has a serial communication interface, simply TTL level into RS-232 level; here using SP3232 chip to achieve this functionality. SP3232 chip required supply voltage low, suitable for portable device applications. Its connection to the external circuit is simple, only need a few µ F capacitor than 0.

System software design system software using C language.

Its main frame as shown in Figure 4.

Figure 4 the main program block diagram for a portable device, the battery life is essential; design to minimize power consumption, making the system as long as possible remain at a low power state.

Therefore, consider the equipment at an appropriate time, automatic shutdown. Here use a timer.When the timer is greater than 0, the system is turned on; when the timer countdown to 0, the system automatically shut down. This timer is a single-chip implementation of Basic Timer. Through software on Basic Timer control register is set, the signal source is set to secondary clock size 32KHz and 256 frequency, then interrupt timing interval control bit set, enables interrupts per second for a time, and every time you advent minus 1 for the timer, which enables the timer 1 per second. How to do this: power on, the timer is initialized to a value greater than 0, 30, and each time a valid key, the system is reinitialized to the values. Therefore, when there is no press any valid key, 30 seconds is automatically switched off, thus achieving power saving purposes. The system also has a real-time clock function, its implementation and the timer is similar. Simply "minus 1 per second" to "1" per second; specifically: each time a break when you are on the second variable to 1, when the seconds value of a variable changes to 60, and 1 to the minutes of the variable, and the second variable again counted from 0; similarly, when you add up to 60 minutes a variable, a variable on the hour, and its own and start counting from 0. And so on, can realize real-time clock and date functions. To meet individual needs, but also increased the clock and the unit setting, average and temperature display, etc. It will not repeat them here. The following main introduce measurement module. First, initialize each port as well as the ADC register; then wait for the drop of blood. When it detects an adequate blood, power off and wait several seconds, the discussion of the full response on the enzyme. Then power-on and in a second read rapidly after. Figure 5 is supporting the use of the blood glucose meter test strips in different concentrations of blood sugar and enzyme reaction for several seconds after the power generated by the current in the curve. It is not difficult to see from the figure, powered a smooth curve more seconds, this is the design uses a "power" to read the SEC. This part of the formula is the key to this design. Table 1 is to use the design of the prototype of the measured data. The data in the table is not difficult to see that the blood glucose and blood glucose test strip measuring repeatability is better – CV < 3%, much higher than the national standard < 7.5% of requirements. Table 1 some experimental data concentration (mg/dl) current (µ A) 5010020030040013.0036.75213.10116.86119.83623.0286.67812.36817.13019.62132.9186.80013.27216.76420.36642.8936.91013.02817.17920.62253.0647.08113.61417.57420.34162.8817.10613.21117.26420.26873.0756.70312.90517.62819.64582.9056.84913.15017.02920.15892.9917.13013.23317.08120.024102.9017.24012.96416.83820.952 mean 2.96596.924913.084617.134820.1833 are variance 2.51532.88962.44561.70652.0898 0.07460.20010.32000.29240.4218CV (%) by the cubic curve fitting, may obtain the glucose value and current value relationship graphs. Figure 6 is the original data piecewise curve and fitting curve comparison chart. Easy to see the two curves are; so in practice you can use a formula instead of Piecewise functions. The curve here is: where x is the current value, unit µ A, Y is the blood glucose values corresponding to the units of mg/dl. In the actual authentication process, the above formula with good accuracy.

Figure 5 data piecewise curve and fitting curve comparison chart

Closing this glucose meter adopts MSP430F435 as its core control unit with 12-bit A/D conversion; sampling accuracy to 1/4096.

In addition to basic functions, the system also adds the alarm cues and serial communication function, so that users can not only be timing measurements, but also through the serial port will measure the results saved to the PC, then use the appropriate software, the data for further processing. This article summarizes the clinically proven formulas with good accuracy. In addition, the Chinese character interface also greatly facilitates the users. Reference: 1MSP430F43X/F44X data sheet TI. Corp.2 Shen Jianhua, Yang yanqin, Zhai Yong-Shu. the MSP430 series single-chip 16-bit low power consumption, 2004.11 principles and applications