Abstract: In response to people's growing concern about heart disease, a new ECG detection system has been introduced, which has the characteristics of small size, strong practicability and low price, especially suitable for home use. At the same time, in order to solve the interface problem with the PC, according to the USB1.1 specification, the PDIUSBD12 interface chip of PHILIPS company is adopted, which greatly improves the speed of data transmission. After testing, the system runs stably and reliably.
With the progress of society and the development of science and technology, people have undergone profound changes in their health concepts, health methods and ways. China is a high-risk area for cardiovascular and cerebrovascular diseases. However, the number of ECG monitoring equipment in most hospitals is small, unsuitable for moving, and the cost is high, which cannot meet the market demand. In order to meet the demand for ECG monitoring equipment and reduce medical costs, an ECG detection system combined with a PC is needed. The bus interface connecting the computer to the peripheral is in various forms, in which the PCI and ISA bus are troublesome to plug and unplug, and the expansion slot is limited; the RS232 serial bus has a slow transmission speed and a small number of serial ports with the host. In recent years, the USB bus interface has sprung up. It has the advantages of hot plugging, plug and play, system expansion and configuration, and efficient data transmission. It overcomes the defects of the traditional bus interface. The ECG monitoring system designed in this paper is also used. This method.
1 hardware circuit design
1.1 The overall structure of the hardware
The overall structure of the ECG detection system designed in this paper is shown in Figure 1. It consists of lead circuit, filter amplifier circuit, microcontroller, flash memory, power conversion circuit and USB interface circuit. The ECG signal is collected from the human body through the electrode, and then enters the A/D of the MCU through the lead circuit and the filter amplifying circuit, and then is stored into the Flash by the MCU, thereby completing the collection of the ECG signal. The system can realize communication with the PC through the USB interface circuit, and the ECG data stored in the Flash is transferred to the PC in the file format, thereby realizing the infinite storage function of the data, and can be programmed on the screen through the VC software. The ECG waveform is displayed. The power conversion circuit is powered by a 9V battery, which is compact and easy to use.
1.2 USB interface circuit
This article uses the PDI-USBD12 from Philips. The PDI-USBD12 is a cost-effective USB device that is fully compliant with the USB 1.1 specification. It is commonly used as a high-speed, general-purpose parallel interface in a microcontroller system that communicates with a microcontroller and supports local DMA transfers. In addition, the PDIUSBD12 integrates many features including SoftConnetTM, GoodLinkTM, programmable clock output, low frequency crystal and termination register sets. All of these features save a lot of money on the system and make it easy to use USB functions on peripherals.
Figure 2 shows the USB interface circuit. The USB interface uses a 4-wire cable. The D+ and D- two lines are used to send signals, and two lines of VDD and GND provide power to the device. The XTAL1 and XTAL2 pins of the PDIUSBD12 are connected to a 6M crystal. The data line and the control line are respectively connected to the I/O port of the single chip microcomputer, and the command and data are sent through the SPCE061 to control the USB interface chip PDIUSBD12, thereby realizing fast and efficient data transmission.
1.3 single chip system
This article uses the 16-bit SPCE061 microcontroller from Lingyang. The microcontroller has a wide supply voltage range (2.4 to 3.6V), the maximum CPU speed is 49.125MHz, and the 8-channel 10-bit ADC (A/D conversion speed is up to 96kbps). ), on-chip 2k RAM, 32k flash, 32 I/O interfaces and more. Flash uses SPR 512k*8 bit SPR4096 from Lingyang Company, and its working voltage is 2.25~2.75V. It has good mutual transmission capability with SPCE061.
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