MSP430 microcontroller based and mobile blood glucose monitoring system design (1)

1 Overview of blood glucose monitoring system

Diabetes is a risk to human health is one of the four major diseases, there is currently no radical approach, accessible only through blood glucose monitoring on diabetes control.

Blood glucose meters, greatly facilitates self monitoring of blood glucose in patients with diabetes. In order to be able to make better use of the wireless network resources that facilitate user anywhere measurement, developed an approach based on mobile communication of blood glucose monitoring system.

Based on mobile communication of blood glucose monitoring system consists of two major components: mobile blood glucose meters and diabetes care center.

Work pattern as shown in Figure 1. Diabetic patients use portable mobile blood glucose monitoring blood glucose at any time, monitoring center through the GSM network to receive patient blood glucose values and feedback appropriate diagnostic findings.

Figure 1 system operating modes

Mobile phone use MotorolA388c, glucose meter is the Jilin University Institute of independent development of instruments for MSP430 microcontroller and enzyme electrode sensor-based blood glucose meter, through the serial port to connect the phone to use mobile keyboard and LCD control displays the blood glucose test results.

That is, a mobile blood glucose meter is the retention of the original mobile phone functions, increased blood glucose testing.

Diabetes care center hardware consists of a single server via the serial port to connect a wireless communications module constitute the MC35, software system is mainly responsible for the complete control of the MC35 receive SMS as well as patient information management and maintenance.

2 the design of mobile blood glucose meter

2.1 system hardware design

MSP430 microcontroller-based blood glucose meter is mainly composed of enzyme electrode sensor, signal processing, data acquisition and processing as well as single-chip microcomputer serial communication with the mobile phone for a few parts, as shown in Figure 2.

Enzyme electrode sensor system using three-electrode, reference electrode, divided on pole and working electrode.

Figure 2 phone glucose meter system block diagram

Front signal processing using analog switches on the electrode to the access circuit to control system provides different work status, signal processing using amplifiers and low-pass filter, the sensor's current signal conversion zoom filter to high-frequency interference, as follow-up circuit data acquisition provides better quality signal, the blood glucose concentration of data acquisition and processing, and serial data communication, using TI's MSP430 series monolithic integrated circuits for a master unit.

In addition, the system with temperature compensation feature, can compensate for environmental temperature on the system test results in error, improve the accuracy of test results. Blood sugar test module volume for 3cm * 1cm so that you can put the phone into the shell, to do blood glucose meter and mobile phone integration, convenience to users of portable and detection.

2.2 blood glucose measuring principle

Determination of blood glucose concentration values through enzyme electrode sensor, when blood glucose infusion, enzyme, the catalytic role in the transmission of electronic materials in carbon electrode surface oxidation is mandatory, the redox reactions of oxidation in the process of formation of glucose concentration of current with linear relationship, by measuring the strength calculation of oxidation current blood sugar concentration values [1].

The electrode and the constant voltage 0.4V, when measured blood dripping in electrode test area, electrode fixed glucose oxidase and blood glucose in a chemical reaction.

After a certain lag phase, enzyme electrode response to current and measured blood glucose concentration in the linear relationship, as shown in Figure 3.

Figure 3 enzyme electrode current change curve

Corresponds to the 2.2-27.8mmol/L of blood sugar concentrations, in response to current enzyme electrode is about A 3-50 μ.

Blood glucose meter is through this correspondence to calculate values for blood glucose concentration is displayed. According to the curve shows the enzyme electrode reaction current spikes in 11s around, so the system before the 11s for enzyme electrode reaction time, as the enzyme electrode 5.3s after the acquisition time. On the current area of integral 5.3s, get power Q, then according to blood glucose concentration known to C0 can be a formula for a standard coefficient K:

Q =∫I(t)dt = K C0

K = Q/ C0

To find out the testing of blood glucose:

Cx = Q/K

Temperature affects the activity of enzyme-catalyzed reaction speed and one of the important factors [2].

Therefore to ensure the accuracy of measurement, temperature compensation must be made. The system test and analysis related to get temperature compensation formula is as follows:

Kt = 0.0133t + 0.067

Considering the temperature compensation, therefore, the blood glucose concentration calculation formula is as follows:

Cx = Q/（K ×Kt）