ECG ARM7-based data acquisition and remote transmission system design (1)

1 Introduction

Heart disease is a serious threat to human health and the life of one of the major diseases.

Statistics show that about 60 per cent of heart attack people die at home, and these patients if timely access to treatment, care, it is entirely possible to avoid death. As a result of a heart attack with a very haphazard and sudden, ECG monitoring from beds, hospital expansion to the community, domestic implementation of remote monitoring, both in terms of reducing the financial burden on patients, or enhance the ability of the hospital service perspective has important practical significance.

2 ECG monitoring terminal hardware design

From the small size, low power consumption, easy design ECG monitoring terminal hardware circuits.

Figure 1 for an entire monitoring terminal hardware diagram, mainly by conditioning circuit, ECG data acquisition module, ARM7 microprocessor module, interface module, power supply module 5-part. The monitoring terminal completes acquisition of ECG and pretreatment, and through real-time monitoring of network traffic sent to a central server, enabling remote real-time monitoring.

2.1 signal conditioning circuits design

Human ECG is a low-frequency small-signal, the amplitude of approximately 10 μ V ~ 5 mV, frequency 0.05 to 100 Hz.

Need to zoom in on thousands of times (i.e. reaching V magnitude) to facilitate the observation, as well as A/D conversion, combined with specific gain also A/d module-measurement van with OK. By ECG cable gets first ECG by instrumentation amplifier with differential amplification AD620, because surface liquid and electrode formation primary batteries between may, resulting in a fixed potential difference exists between the electrodes, level 1 differential amplifier gain must not be too high, otherwise easily saturated, so 1 gain election to 20; in order to make the signal meets the requirements of A/D conversion, signal amplification-V magnitude, so set the secondary amplification is 30, here used ordinary LM324 quad operational amplifier. Because of the ECG is often mixed with DC and baseline drift interference, so it should be at level 1 and secondary amplification circuit between the high-pass filter, can effectively avoid the ECG's baseline drift, the high-frequency interference signals through the amplifier input circuit and a cut-off frequency of 100 Hz of second-order low-pass filter to filter out. In addition, by removing the power frequency 50 Hz notch filter. The signal processing, ECG access microprocessor LPC2210 of P0.27 pin (AIN0) from its internal A/D conversion module completes A/D conversion. According to the sampling theorem, sampling frequency should ensure greater than 2 x, A/D conversion of sampling frequency is set to 500 Hz. Figure 2 is a signal conditioning circuits.

2.2 ARM7 microprocessor and peripheral circuits

LPC2210 is PHILIPS Corporation support based on a real time simulation and keep track of 16/32-bit ARM7TDMI microcontroller CPU.

The device has 144 pin package, extremely low power consumption, more 32-bit timer, 8-channel 10-bit A/D converters, PWM output and up to nine external interrupts that make it suitable for industrial control, medical systems, access control and electronic point-of-sale (POS).