ECG Acquisition in a Computer - ECG Acquisition and Automated Remote Processing - page 60

Data Storage in
text file

Microcontroller-based
serial communication
system with level
shifter, amplifier, ADC
and connector

PC

ECG source

ECG signal

RS-232
Communications GUI based

Toolsets and
ECG analysis
software

User command

Wave durations
and intervals on
GUI front panel

DAS card

Fig. 3.7 Block diagram of the PC-based ECG DAS

developed by us for single-channel ECG acquisition and computer-based analysis
is described. The system is useful for preliminary level diagnosis of a cardiac
patient in a health care unit. An 8051 MCU-based stand-alone DAS card is
developed, which transmits the ECG samples using the serial port of the PC [ 25 ].
A short-duration data (6-8 beats) are acquired for offline analysis using application
software, which is developed in MATLAB platform. A graphical user interface
provides soft switches and menu-driven front end for easy operation to the user.
The functional block diagram of the developed system is shown in Fig. 3.7 .
The DAS card contains an analog front end, single-channel AD converter, and
an AT89C51 MCU to convert the ECG samples into a serial data stream con-
forming RS-232 protocol. The serial data stream is transmitted at a speed of
19.2 kbps to the PC for temporary storage in a data file (*.txt format). Finally, a
time-stamped data file is generated for time-plane analysis of samples for feature
extraction. The extracted time-plane features along with a lead data plot are
generated on the GUI front panel.

3.5 Serial Communication Between DAS Card
and Computer

3.5.1 Basics of Serial Communication

Over the years, serial port has become the popular choice for communication
between embedded systems or between embedded systems and PC. Most of the
laboratory-based DAS employs one or other form of serial communication pro-
tocol for transmission of sensor's signal to the host PC. The most important
features of serial communications are as follows:

1. Saves cable cost, since only two/three wires are enough to achieve full-duplex
communication.