ARM9-based heart defibrillation simulation system design (1)

With the development of the society, people's health consciousness more and more strong, so the doctor training has become a very important link.

Cardiac defibrillation technology as one of the main medical training, if the operations specification, skilled, often at the last minute can save lives in times of crisis, in training, if able to realistically simulate emergency defibrillation scenarios, would be a good learning experience. Therefore, first aid, invasive clinical operations training, medical simulation teaching increasingly shown its low cost, high repeatability, teaching high efficiency and meet the ethical requirements.

Defibrillation simulation system can choose 34 State (including adult and children two categories) or medical monitor, defibrillator simulate more realistic.

The trainees can perform different energy defibrillator training, at the same time, this also makes it easy for teachers to test students ' learning results.

The system is based on the principle of the ECG and patient monitors signal synthesis theory developed in strict accordance with the relevant provisions of the medical, the resulting wave reached the purpose of medical teaching.

In the relevant disease ECG's key point reaches more realistic effect, when the system receives a high voltage defibrillation signal, depending on the system of advance settings, to wave converter. The system can be used in medical training institutions for training tools to enable students to quickly master cardiac defibrillation. The system simulation with first aid, monitor, have broad market prospects.

This article describes the heart defibrillation simulation system is the core for the control of ARM9, take full advantage of ARM9 rich i/o resources and powerful processing capabilities.

It uses the embedded development programme, and considering the system's versatility and usability, system output signal amplitude 0 ~ 5 mV continuously output room, supraventricular premature models, etc., can also produce a cycle of 1 s, ms pulse width is 100, the mV ranges 1 square. Easy to calibrate the monitor, the signal is a three-lead synchronization signal output.

1 system architecture and design

The system mainly includes the ARM9 central processing units, high voltage defibrillation signal acquisition module, D/A conversion modules, and monitor signal matching module and ECG waveform simulation and data extraction, application design, etc.

This system uses the ARM9 embedded development platforms, the following is the main structure of ARM9 processor and its features.

(1) 32 b fixed-point RISC processor, improved ARM/Thumb code weaving, multiplier, enhanced support for real-time (real-TIme) debugging;

(2) on-chip SRAM, instruction and data and instructions and data storage capacity adjustable;

(3) chip instructions and data, high-speed buffers (Cache) capacities from 4 KB ~ l MB:

(4) set protection unit (Protoction Unit), very suitable for embedded applications in memory to be fragmented and protection;

(5) the introduction of AMBA AHB bus interface for peripherals provide a unified address and data bus;

(6) support for external coprocessor instructions and data bus with a simple handshake signalling support;

(7) support standard basic logical unit scan test method;

(8) support BIST (Built-in-self-test);

(9) supports the embedded tracking macros, modules, support provides real-time tracking of instructions and data.

Simulation of cardiac defibrillation system overall design scheme, as shown in Figure 1.

2 system hardware design

This part is mainly divided into ARM9 hardware platform, D/A conversion, filtering circuit, high-voltage defibrillation signal acquisition, its system hardware connection diagram shown in Figure 2.

System under the control of the ARM9, D/A conversion to waveform data converted to analog output. When receiving a high voltage acquisition signal, the processor will convert the output of another ECG waveform diagram.

2.1 D/A conversion and resistance attenuation networks

This section is the core of the system, to ensure the system's stability and ECG signals, D/A conversion chips using 8-bit parallel DAC0832 chip, 12-V single supply, each DAC with separate reference inputs, data provided by the ARM9 to transform the output part adopts 4-order Butterworth filter, the output waveform with decay after the ECG, the filter after the output waveform peak up to 10 V, through the resistor divider network get 0 ~ 5 mV voltage output ranges.

Considering that to adopt the triple D/A, if each one exclusive 8 I/O ports, plus a number of control port, processor provides i/o port number distant do not meet the requirements, so plan to adopt common data ports, external I/O port films selected to implement, so you can save 16 I/O port, also meets the requirements of the signal output synchronism.

2.2 high voltage signal circuit design

The partial acquisition defibrillator on high-voltage discharge signals, due to the high-voltage defibrillation signals have discharge current with bi-directional, and discharge time only 4 ms, transient voltage up to 3 000 V, security property to be fully taken into account.

The circuit shown in Figure 3.