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 DB 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/.

     You may also find that an existing database of digitally recorded signals may be useful for your studies. Four such databases are currently available on CD-ROM (the MIT-BIH Arrhythmia Database, the European ST-T Database, the MIT-BIH Polysomnographic Database, and the MGH/MF Waveform Database), and several more databases in this format are in preparation. These disks are compatible with any CD-ROM drive.

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. (Newer 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 a removable disk, then read it on the WAVE host. Devices such as IOmega's 100 Mb Zip or 1 Gb Jaz drives are suitable for this purpose; the SCSI versions of these devices are usable under Linux, Solaris, and SunOS. For high-speed or high-volume digitization, the Jaz drive is a good choice. An advantage of this approach is that the removable disks are inexpensive enough to be used for archival storage of the data.