Display Driver Board / El Display - GE Giraffe Service Manual

Chapter 1: Functional Description
The motor driver circuit turns the DC motor coils in the incubator airflow fan motor on and off based on
feedback from the hall effect position sensors. This integrated circuit can also vary the speed and brake the
motor based on input signals from the Control Board.
The airflow sensor consists of an optocoupler that outputs a clocking pulse proportional to the fan movement.
The signal is AC coupled to eliminate offset voltages and drifts. The resulting pulse is half wave rectified and
stored in a capacitor to yield a DC voltage proportional to the fan speed. If the fan stops or there is no fan, this
DC voltage becomes zero. The output signal is provide to the Control Board to indicate proper airflow motor
operation.
The elevating base motor control circuits consist of a series of three relays. For the Giraffe Incubator, the speed
relay and the E/H select relay are always switched to the same position. The speed relay connects the 15 volt
secondaries of the toroidal transformer in a series (drive at 30 volts) for raising or lowering the elevating base.
The direction relay reverses the polarity of the voltage output from the speed relay depending on the direction
of travel. The E/H select relay switches the output voltage from the direction relay to the elevating base motor.
The Relay Board interfaces the user and system status input switch signals to the Control Board. Switch signals
include, e-base activation, humidifier reservoir, and water level status.

1.3 Display Driver Board / EL Display

The Display Driver board contains the same Intel microcontroller as the Control board. The processor on the
display board is used to control the EL display contents and monitor user inputs received from the membrane
switch panel and rotary encoder knob.
There are two groups of digital inputs: membrane switch panel and rotary encoder knob. The membrane
switches are pulled high; pressing the switch grounds the input. The encoder also has a switch, and two
optically isolated lines that pulse out of phase with each other. The number of pulses represents the number of
steps the knob rotates. The phase of the pulses represents the direction of the knob rotation.
The display board system memory consists of a programmable read-only memory (PROM) and static random
access memory (SRAM).
The RS-485 integrated circuit converts the RS-232 TTL signals from the microcontroller to RS-485 signals for the
bus.
The timekeeping RAM has a battery integrated into the chip so that the time and date run are kept current
even with the power off. The battery has a minimum life of 10 years. Operator configuration values, patient
information (trending), and the error log are stored in this RAM.
The graphics controller is an S-MOS VGA controller. The graphics controller interfaces the data from the video
RAM to the EL display. The controller also synchronizes the display using a horizontal pulse (LP) and a vertical
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