Electrocardiogram (ECG) is an important tool for the diagnosis of heart disease. Conventional electrocardiogram is a short-term ECG activity recorded by the hospital's electrocardiograph in a recumbent situation. Because of a large chance and suddenness in heart attack, routine ECG is performed during non-onset period to obtain disease information. The chance is very low. Therefore, it is of great practical significance to extend ECG monitoring from the bedside to the hospital to achieve real-time remote monitoring.
The rapid spread of the Internet, especially wireless networks, has led to the maturity of embedded technology applications. In addition, the importance of ECG monitoring for heart disease diagnosis also makes remote monitoring a reality.
This paper mainly studies and designs a practical portable mobile ECG monitoring system. Through the system, the patient's ECG signal can be wirelessly transmitted to the PC set in the hospital through the GPRS network anytime and anywhere, or the ECG data can be stored in the system first, and then the high-speed playback can be realized through the USB.
First, the overall design of the system
The portable mobile ECG monitoring system designed in this paper consists of three parts: ECG monitor, communication network and monitoring center (as shown in Figure 1). The working process is as follows:
Figure 1: Overall block diagram of a portable ECG monitoring system.
The ECG monitor is carried by the patient, and the user's ECG data can be collected at any time through the adhesive electrode, amplified, filtered, A/D converted, and then stored in the serial flash memory. After storing the ECG data for a certain period of time, it can be wirelessly accessed via GPRS, and the data is transmitted to the host computer located in the monitoring center by using the wireless network. It can also be directly connected to the host computer via USB for local high-speed playback.
This article will focus on the design of the ECG monitor. Because it is a portable device, it must be designed to minimize power consumption, size, and cost. After repeated analysis and comparison, it was decided to use Z-World's industrial-grade control chip Rabbit3000 microprocessor as the main chip of the ECG monitor.
Although the Rabbit3000 is an 8-bit microprocessor, it has a memory space of 1M and a clock speed of 22M. It has a wealth of interface resources, a total of 40 parallel I / O line (shared with the serial port). In addition, the device consumes very little power, the processor clock can be driven by the 32.768KHz oscillator, and the main oscillator is powered down. At this point, the current is about 100μA, and the processor can still maintain the execution speed of 10,000 instructions per second.
Second, the system hardware design
In the overall hardware design, the Rabbit3000 high-performance microprocessor is the core, and the external interface is used to expand 512K parallel flash and 512K SRAM, the storage space reaches 1M, and the USB interface is extended. Serial Flash, A/D conversion and wireless module MC35 are extended with a serial interface. The following focuses on the hardware design of the wireless module and the USB module.
1. Wireless module MC35 hardware design
The wireless module is responsible for completing the wireless transmission of the ECG data. In order to achieve this function, the system uses the MC35 module of Siemens. This is Siemens' first GSM/GPRS module that supports GPRS. It is compact and easy to integrate into portable terminals. Through the serial port connection, the module is controlled and data transmitted using the AT command.
The MC35 module of Siemens has a 40-pin zero insertion force connector, which provides serial interface, audio interface, SIM interface, status pin, power interface and other interfaces through which the SIM card holder and antenna are connected. And the main controller is connected. The serial interfaces TXD0 and RXD0 of the MC35 are connected to the serial port B of the Rabbit3000, that is, pins TXB and RXB (PC4 and PC5) to implement communication with the MC35. The MC35's IGT pin is its enable pin and requires an open drain driver drive. The port E of the Rabbit3000 has a strong driving capability, so PE5 is selected as the startup control line of the MC35. There are power input pins, power output pins and charging pins in the MC35's power interface, where the charging pins can be used to charge the battery. The system is battery powered or externally charged. as shown in picture 2.
Two points to note when designing: This system uses battery power. Since the MC35 needs to provide 2A peak current in the uplink transmission, this will cause a sudden drop in voltage. Therefore, design a circuit with a large enough capacitance to prevent the voltage from dropping suddenly. In the design of the SIM card circuit, you need to pay attention to the problem of electromagnetic compatibility, otherwise it will affect the communication effect of the MC35, and even cause the MC35 to not work properly.
Figure 2: Hardware connection diagram of the MC35 module.
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