DESIGN OF SAFE MEDICAL DEVICE PROTOTYPES - Design and Development of Medical Electronic Instrumentation - page 119

graphy instruments. You will probably fi find an elegant design comprising instrumentation

ampli ers for each lead followed directly by an A/D converter and optical isolation lead-

ing to a DSP microprocessor. Often, the complete applied part is contained within a
“medallion” to which the patient leads are directly connected, and digital signals to and
from the embedded microcomputer are relayed through optical

fi

ber.
The sample circuit of Figure 3.15 is not as complex as those of high-end commer-
cial instruments but provides a very simple and convenient interface between analog-
output applied parts and most PCs on the market. Instead of connecting to the computer's

fi

Figure 3.15 A MAX187 low-power 12-bit A/D converter IC forms the core of the isolated A/D converter module. A two-wire serial inter-
face conveys data from the MAX187 through optoisolators back to the PC through the printer port. The PC also controls an isolated signal
multiplexer that allows one of eight analog signals to be presented to the input of the A/D.