Design and implementation of multi-parameter monitor based on TI OMAP3 platform

introduction

In modern medicine, the use of multi-parameter monitors to monitor critically ill patients in real time can timely understand their cardiopulmonary function, blood pressure, oxygenation capacity and other comprehensive factors, which plays a very important role in the treatment of patients. Multi-parameter monitors have been widely used in ward care and emergency systems.

Multi-parameter monitors based on traditional PC platforms are expensive, bulky, and complex to operate, and their scope of use is limited. Portable multi-parameter monitors based on single-chip microcomputers have low computing power, single functions, and simple interfaces, and can only display and store simple signals. This paper uses the Texas Instruments (TI) ARM+DSP dual-core processor OMAP3530 as the core, expands the parameter acquisition front end, touch screen, SD card storage circuit, and network access circuit modules, and designs and implements a new multi-parameter monitor with real-time detection, display, storage, and network transmission functions. Based on the excellent performance of the dual-core chip, the system can use efficient and complex algorithms to quickly and accurately detect, remove noise, and optimize various life parameters, while Google Android's rich application support provides the monitor with a good monitoring interface, network functions, and application scalability. Doctors can use this monitor to obtain patient information in real time or remotely, and users can also measure it themselves at home. This will be an important development direction for the new generation of "digital medical communities/hospitals".

System Architecture

Processing core

The OMAP3530 processor is manufactured using a 65nm low-power process and integrates a 600MHz Cortex-A8 flexible core and a 430MHz TMS320C64x+ DSP core[1]. The dual-core structure of ARM+DSP optimizes the efficiency of the operating system and the execution of code. The ARM side is responsible for system control, while the DSP side undertakes the heavy real-time signal processing tasks, thus successfully solving the problem of the best combination of performance and power consumption. The dual-core OMAP3530 is very suitable for the design of a new multi-parameter monitor. Low power consumption can better realize the portability of the monitor and meet special needs such as field rescue; ARM's support for multiple operating systems can ensure the stability of the system and a good monitoring interface; the powerful computing power of the DSP can ensure fast, accurate and complex analysis and processing of various life parameters.

Hardware Architecture

The system block diagram is shown in Figure 1. The design of the monitor adopts the classic C/S (Client/Server) architecture. It can be used offline or transmit data to a remote PC server through Ethernet or Wi-Fi network. After the various vital signs of the human body are obtained through sensors such as lead electrodes, blood oxygen probes, and cuffs, they are de-noised, amplified, and A/D converted at the parameter acquisition front end, and then sent to OMAP3530 through the serial port for detection, display, storage, and network transmission.

Software Architecture

Android is a truly open mobile device integrated platform based on Linux, launched by Google and the Open Handset Alliance (OHA). From the perspective of software structure, the Android system is divided into four levels: Linux operating system and driver, local code framework, Java framework and Java application. Figure 2 is a diagram of the software architecture of this system. The multi-parameter acquisition front end communicates with OMAP3530 through an asynchronous serial port. Since Java itself does not provide a serial port class library, JNI (Java Native Interface) must be used to implement data transmission between the application layer and the serial port hardware. Data acquisition, processing, display and network transmission use multi-threading and queue buffer mechanisms to ensure the real-time and integrity of data. The network uses a C/S architecture to give full play to the hardware advantages on the server and complete the display and analysis of more monitoring information.

Key Design

Parameter collection front end

The ECG module in the front end uses an instrumentation amplifier and an operational amplifier to form a two-stage amplifier circuit to amplify the weak ECG signal by 200 times, and a right leg drive circuit is added to the design to overcome the 50Hz power frequency common mode interference [2]. The measurement of blood oxygen is based on the different absorption degrees of different specific wavelengths of light emitted by the blood oxygen sensor by various hemoglobins in the blood. Blood pressure is measured using a vibration non-invasive method. First, an inflated cuff blocks the blood flow in the upper arm artery. The systolic pressure, diastolic pressure and mean pressure of the artery are identified by detecting the fluctuation amplitude of the pressure in the cuff caused by blood flowing through the elastic artery [3]. The measurement of respiratory rate shares the front end lead electrode of the ECG module and uses the respiratory impedance method to detect the respiratory rate of the human body based on the changes in the chest relaxation and lung impedance during breathing [4]. The body temperature measurement circuit in the design uses a Wheatstone bridge, and a thermistor is connected to one arm of the bridge. By measuring the unbalanced output of the bridge, the body temperature can be measured.

High-speed PCB design

The LPDDR data bus frequency used in the system is as high as 330MHz, which is a typical high-speed circuit. Factors such as the electrical characteristics of the device pins, PCB (printed circuit board) parameters, layout and wiring of high-speed signals must be considered, otherwise it is easy to cause the system to work unstably or even fail to work. The PCB adopts a 6-layer board design, FR4 board, and the layering scheme is: top layer-ground layer-routing layer-power layer-ground layer-bottom layer. In high-speed PCB design, the signals must be grouped first, and then the wiring rules must be determined, as shown in Table 1.

Guardianship Program Design

The monitoring program needs to complete the functions of collecting, receiving, displaying, storing and transmitting the parameters over the network. The program uses JNI technology to provide the Java layer with an access interface to the serial port, and creates input/output streams through file descriptor objects for serial communication. To ensure the real-time and integrity of data collection, the design adopts a multi-threaded and double-buffered mechanism. If remote monitoring is enabled, the system will dynamically generate a thread to complete the task of data transmission. Waveform display is a difficult point in interface design. Considering the consumption of the page refresh and network transmission during data collection and waveform drawing, as well as the size limit of the screen, the waveform drawing view adopts a multi-buffered mechanism to avoid flickering when the screen is refreshed. In order to maintain the single-threaded model of Android, the design uses a message notification mechanism to complete the communication between the non-main interface thread and the main interface thread [5]. The monitoring interface is shown in Figure 3.

Conclusion

The test results of the prototype show that the multi-parameter monitor designed based on the OMAP3530 dual-core processor can realize the real-time detection, display, storage and network transmission of six vital parameters, including ECG, heart rate, blood oxygen, blood pressure, respiratory rate and body temperature. The monitor is easy to operate, low cost, low power consumption, powerful and portable, which makes it have a wide range of applications and good market value. With the improvement of people's medical awareness and the improvement of the medical system, this type of monitor will be more and more widely used in personal medical care, hospital rescue, field emergency and remote medical monitoring.