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Data acquisition and digitization
PC-based data acquisition is a good choice given the large number of ADC boards
available; note, however, that Linux drivers for these boards are rare.
The WFDB Software Package available separately from MIT includes an MS-DOS
program (named sample) for digitization and replay of analog signals
using a DAP 1200- or 2400-series data acquisition board (available from
Microstar Laboratories,
http://www.mstarlabs.com/).
Note that the WAVE host
must be able
to read the signal files. If you use an MS-DOS data acquisition
program, this can be accomplished in several ways:
- The data acquisition PC can be set up to boot either Linux
or MS-DOS,
and when running WAVE under Linux, signal
files written to MS-DOS file systems can be read directly. (Current
versions of Linux can also read files in Windows NT, Windows 95, and
OS/2 file systems.)
- Alternatively, you can transfer the digitized
signals to another system acting as the WAVE host, either during
digitization (by writing to a network drive) or afterwards. Since
signal files are usually very large, Ethernet
transmission is
recommended. To set up a minimal Ethernet including a Sun workstation
or Linux PC and an MS-DOS PC, you will need an Ethernet card for each
PC (usually around US$100; Sun workstations have built-in Ethernet
adapters but may require external transceivers, usually around $50),
TCP/IP software for the PC (such as Sun's PC-NFS, about $300), and
miscellaneous cabling and terminators ($20 or less). For a truly
minimal network of only two systems, see the Linux Ethernet-HOWTO for
details on how to connect two UTP interfaces without using a hub. You
will need a hub (US$150 or more) to connect more than two systems,
unless you are able to use the older `thin' (10 Base 2) Ethernet. If
you use sample for digitization, signal files can be written
directly on the host system's drive at rates up to 80,000 samples per
second using PC-NFS (or up to 100,000 samples per second on local
disks). This configuration allows you to examine the signal files
using WAVE as the data are being acquired; although WAVE does
not currently support real-time, continuously updated display of
incoming data, it is not difficult to create a log file for WAVE
that can be used to drive a continuously updated time-delayed display
(see
a note about automatic scrolling
for details).
- You can write digitized data to removable storage, then read the data on the
WAVE host. Many devices are suitable for this purpose; consider
using writable CDs or DVDs, USB or Firewire disk drives, or compact
flash memory cards.
You may also find that an existing database of
digitally recorded signals may be useful for your studies. PhysioNet, at
http://www.physionet.org/,,
offers free on-line access to over 30 such databases with thousands of
recordings ranging in length from a few seconds to several days.
These include all or most of the MIT-BIH Arrhythmia Database, the
European ST-T Database, the MIT-BIH Polysomnographic Database, the
MGH/MF Waveform Database, and the Long-Term ST Database (which are
also available on CD-ROMs from their creators), and many other
databases available only via PhysioNet. WAVE can read these
databases directly from PhysioNet without downloading them first (the
WFDB library, which handles reading and writing data for WAVE ,
contains HTTP client code that permits applications such as WAVE to
read input with equal ease from local disks or remote web servers).
This is an excellent way to explore PhysioBank (PhysioNet's collection
of signal databases).
Next: About Linux
Up: System Requirements for WAVE
Previous: X11 window managers
George B. Moody (george@mit.edu)
2003-10-17