Design of wearable ECG monitoring system based on ZigBee

Abstract: A design scheme of wearable ECG medical monitoring system is proposed. This scheme uses ZigBee technology to construct a number of wearable ECG detection terminals to construct a corresponding wireless sensor network according to requirements. The service host completes data aggregation, storage and display. A series of information management functions. The wireless sensor network node is mainly composed of an ECG monitoring chip BMD101, an STC microprocessor, and a CC2530 wireless transceiver module. The results of the design work show that the program is feasible and won the third prize of the 14th Guangdong Electronic Design Competition.

0 Preface

The ECG detection monitor is an important component of the dynamic electrocardiogram analysis system for clinical diagnosis and monitoring of cardiovascular diseases [1], and plays an increasingly important role in effectively preventing and monitoring heart diseases. However, conventional ECG monitors require patients to be in a static measurement, limited by time, medical facilities, etc., and cannot adapt to the sudden, intermittent, and transient characteristics of the patient's onset. At the same time, conventional monitors are expensive, bulky, and difficult to move, and cannot meet the needs of patients for long-term real-time monitoring, recording, and analysis. To this end, many new portable technology solutions [2-3] and wireless communication technology solutions have been proposed [4-9], but generally do not meet the wearable requirements. Relevant information shows that by 2017, there will be 640 million wearable devices in the world, which are mainly used to monitor people's physical and mental health. From wearable health tracking devices, relaxation meditation monitoring devices, sleep monitoring devices, cardiac condition monitoring devices to smart watches and eyewear, wearable products have broad room for growth.

This paper proposes a design scheme of a wearable ECG monitoring system based on the dedicated ECG chip BMD101 to meet the needs of medical care under the new situation of data management information processing such as real-time monitoring and data storage, processing and alarm.

1 ECG chip BMD101

BMD101 is the third-generation SoC chip for biosignal detection and processing introduced by NeuroSky in the United States. Figure 1(a) shows the 8-pin package. The 1 pin is the chip select control terminal, the 2 pin is the ECG analog input positive terminal, the 3 pin is the ECG analog input negative terminal, the 4 and 5 pins are the UART transceiver terminals, the 6 pins are the system reset terminal, and the 7 and 8 pins are the power supply terminals. The chip is small in size, low in power consumption and uses a dry electrode sensor. The interface circuit with the microprocessor is realized by the UART shown in FIG. 1(b), and thus can be conveniently applied to wearable devices and portable devices.

The BMD101 analog front end is mainly composed of a low noise amplifier, an ADC analog-to-digital converter, and a detection circuit for detecting the sensor falling off, and has excellent noise cancellation function. The biosignal from V to mV can be collected with a sampling frequency of 512 Hz and an analog to digital converter with 16-bit accuracy. The result is filtered by a low frequency filter with a cutoff frequency of 100 Hz and output via the UART.

The BMD101 packet output format uses the ThinkGear Packets type, as shown in Figure 2(a) [10]: The header of the packet consists of two sync frames and one byte that tells the valid data length; the actual data code is sent immediately. Finally, a checksum of valid data is sent. The valid data is also internally defined according to a certain format to determine the nature of the data sent and its specific characterization content and meaning, as shown in Figure 2(b) and Table 1. The valid data begins with 0 or more spreading codes (EXCODE) indicating the spreading code level, and the spreading code level is used to indicate the data type to which the subsequent code belongs. This is followed by the length of the data and the length of the data, and finally the data value corresponding to the code.

The pseudo code for the interpretation of the ECG signal is as follows:

(1) Read wait sync frame byte (0xAA);

(2) reading the next byte and determining whether it is a sync frame byte (0xAA), if not returning to step (1);

(3) Read the data length byte [PLENGTH];

(4) reading valid data and performing checksum operation;

(5) Invert the low byte of the checksum accumulator;

(6) Check the checksum [CRC] of the data to determine whether they are consistent, and return to step (1) if they are inconsistent;

(7) Enter the data interpretation loop until the interpretation is complete:

1 Explain and count the number of extension codes [EXCODE] (0x55);

2 Explain the current data stream code [CODE];

3 If possible, explain the length of the current data;

4 interpreting and processing data information of the data stream based on information such as the previous spreading code and length;

5 If the data stream is not explained, go back to step 1.

In short, the core of BMD101 is a powerful system management unit. It is responsible for the configuration of the entire system, operation management, internal and external communication, proprietary algorithm calculation and power management, which guarantees the application of wearable devices.

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