Honeywell BENDIX/KING KAP 140 Maintenance Manual page 88

4.3.16 KC 140 ALERTING OUTPUTS
PIN
P1401 -- 20
P1402 -- 44
These outputs provide a low--side current sink for the cockpit annunciators. One side of the
annunciator is wired to aircraft power and the other side of the annunciator is wired to the KC 140
output pin. The software and/or hardware in the KC 140 controls a transistor which turns on or off
each annunciator. This transistor can sink ~120mA and begins to go into current limit around 600
mA.
The TONE_ALERT output is typically wired to a SONALERT buzzer and can be controlled via the
DISCRETE OUTPUTS diagnostic page (USING Audio Alert). The TRIM_FAIL output is wired to
the TRIM FAIL annunciator in the cockpit and is controlled by hardware and can be tested through
diagnostics mode by setting up the hardware to fail the autotrim runaway or manual trim runaway
monitor. In certain aircraft installations, the TRIM_FAIL annunciator is wired through a diode to
the TRIM_FAIL output of the KC 140.
4.3.17 KC 140 PHOTOCELL (DISPLAY BRIGHTNESS)
The photocell on the front bezel of the KC 140 flight computer senses the ambient light in the
cockpit of the aircraft and provides a voltage based on the amount of light it receives. Based on
the voltage output by the photocell, the KC 140 processor varies the duty cycle of a PWM signal
that controls the brightness of the KC 140 display. The more light the photocell receives, the
greater duty cycle the KC 140 processor generates for the display. The photocell voltage can be
viewed on the ANALOG VOLTAGE INPUTS diagnostic page. When the photocell is completely
covered, the photocell output voltage in diagnostic pages should be ~0 V. When the photocell is
completely saturated with ambient light, the photocell output voltage in the diagnostic pages
should be >4.5 V. In addition to the photocell, the potentiometer on the front of the bezel can adjust
the overall display brightness level.
Revision 2, Dec/2002
CS:15574F02.IDU
BENDIX/KING
KAP 140
DESCRIPTION
TONE_ALERT
TRIM_FAIL
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