Table of Contents
Chapter 1: Functional Description
This chapter provides a functional description for the Giraffe OmniBed, including sections representing each
of the four boards. Refer to "Figure 1-1 Block Diagram" and section "6.5 Wiring Diagrams" when studying this
chapter.
1.1 Control Board
The Intel 80C188EC microcontroller is an enhanced X86 processor with many on-board peripheral features,
such as a interrupt controller, DMA controller, peripheral chip select driver, programmable timers, etc. The two
programmable timers are used to control the two heaters (bed and radiant). The input to these timers is line
frequency. This allows the control signal to be synchronized with the line frequency to better control the zero-
crossing solid state relays. The on-board interrupt controller has several interrupts: analog-to-digital converter
(ADC) conversion ready signal, overtemperature comparator output, watchdog output, power fail signal, and
module interrupt signal from the system data bus. The microcontroller external bus is a multiplexed address
and data bus.
The system memory consists of a programmable read-only memory (PROM) and static random access memory
(SRAM). The EEPROM is used for calibration and biomedical configuration values. This memory holds the data
even after power is turned off.
The RS-485 integrated circuit converts the RS-232 TTL signals from the microcontroller to RS-485 signals for the
bus. This bus is the main communications bus from the control board to the display board, scale, and servo
oxygen board.
There are two isolation transceivers used to isolate the circuits powered by +5V and the circuits powered by
+5VSTBY (battery backup).
The board contains a 16 channel multiplexer. There are seven temperature measurement channels. These
channels measure the two patient probes and the compartment probe (with two thermistors each), and the
heat sink sensor used to measure the heat sink temperature. Additional channels include the humidity sensor
(RHIN), LINE COMP & LINE COMP2, 5 Volts, Motor current, Vthref, VDAC, and 1.2Vind.
Attached to the compartment probe connection is the relative humidity signal conditioning circuitry. The 1V
reference that is used for the analog circuitry is also the maximum input voltage and the offset voltage for the
ADC. This yields a purely ratiometric system.
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Troubleshooting
