Electrical System
Chapter 3: Theory of Operation
Affinity® Four Birthing Bed Service Manual (195826 REV 2) 3 - 7
3
Pendant Inputs
The pendant is connected to logic control P.C. board connector P14 and the pendant functions are only
the three motor articulation functions. These signals go directly to the CPLD and do not use the SPI
interface. These signals have switch de-bounce and ESD protection components.
Oscillator Circuits
IC, U11, is an un-buffered inverter used to create two oscillators. The 1.0Hz oscillator is used for the
yellow nurse call flashing and flashing of the battery charge indicator LED. The output should be 1.0Hz
+/- 33%. The other oscillator is 24KHz +/- 10% and is used to drive the air solenoids and used to create
the SPI clock. The duty cycle should be 50% +/- 5%.
Ripple Counter Oscillators
U1 is used for the wakeup timer and the oscillator output is 1.1KHz +/- 20%. U3 is used for the SPI
problem watchdog timer and the oscillator output is 250.0Hz +/- 20%.
CAREGIVER BOARD OPERATION
Each control on the caregiver board and each control on the patient board is parallel connected to a
parallel-in serial-out 32 bit shift register. When the shift_load/ signal goes low, the control status is
presented to the shift register latch. Then when the shift_load/ signal goes high, the control data is
latched and will start to shift into the control board when the clock starts. LEDs are driven individually
from the control board to show to the user various bed status. The wakeup circuit is connected to both
caregiver and patient nurse call controls and caregiver articulation controls only.
SIDECOM® BOARD OPERATION
The SideCom® board (relay junction), 64547, serves as the interface between the bed and the hospital
headwall entertainment, lighting, and nurse call systems. It isolates the circuits between the headwall
systems and the bed secondary circuits. Inputs and outputs come from the FPGA or directly from the
siderails via connector P6.
The speaker/microphone and volume control lines are directly connected from the siderail to the
headwall with only the wire insulation as isolation. There are 7 relays that provide left and right, direct
and indirect lighting, left and right radio control, and TV channel control. The universal TV controller
(UTV), U3, provides signals for the more modern hospital TVs. The UTV signal is isolated by K5. The
board has jumpers on it to provide for the older TVs but is rarely used anymore. The nurse call phono
jack, P4, is used for hand control nurse call controls or sip and puff controls. When the dummy plug is
removed a nurse call is made.
The P5 connector connects directly to the hospital headwall SideCom® interface.
Refer to the schematic diagram at the end of this section (see page 3-9) for specific information about
the cabling.
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