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7. C omponent Functions and Parts
This chapter provides a detailed description of the functions of the
main components of the QA-45, as well as a parts list for cross-ref-
erence.
The QA-45 is based on 4 circuit boards: a processor board, sensor
board, ECG signal distribution board and pacer module. The boards
are described in 12 circuit diagrams which are located in Appendix
A. Diagrams 1 through 4 describe the processor board; Diagrams 5
through 8 describe the sensor board; Diagrams 9 and 10 describe the
ECG distribution board, and Diagrams 11 and 12 describe the pacer
module.
7.1 Theory of Operation
The QA-45 Defibrillator/Transcutaneous Pacer Analyzer is a battery
powered unit, based on a microprocessor and analogue electronics
with precision data acquisition circuits. Using controls on the front
panel of the unit, one can analyze defibrillator and pacer pulses,
when these are discharged through built-in load resistors. The unit
can also generate a number of different ECG, test and stimulus sig-
nals. The measurement results appear on an LCD display, and can
be output to a printer. A serial port (RS-232C) makes remote control
from a PC possible. All measurement and control signals are con-
nected via contacts on the top and rear of the unit. To operate the
unit, there are 5 soft keys linked with menus on the LCD display.
7.2 Processor Board
(Refer to QA-45 Processor Board Component Location Diagram
and Schematic Diagrams 1-3)
1. Printer Output (Schematic Diagram 1) . QA-45 has a printer
output with a standard 25-pin D-sub contact for Centronics

in-
terface. The output is based on 3 HCMOS circuits: IC9, IC10
and IC11. All the circuits are connected to I/O-ports on the mi-
croprocessor. ICll is a latch for the 8 parallel data lines. IC9 is
the driver for outgoing control signals, while IC10 is a buffer
for incoming control signals. RP1 contains pull-up resistors for
the input lines. All connections to the printer contact are filtered
to reduce high frequency radiation.
2. Serial Port (Schematic Diagram 1) . The serial port is suitable
for 9-pin RS-232C format. The QA-45 is configured as DTE
(data terminal equipment) and should be connected to, for ex-
ample, a PC with a null-modem cable. IC6 is the driver for the
data signals. All handshakes take place via software. The con-
trol signals are routed back to the contact.
3. Curve Generator (Schematic Diagram 1) .
1