Physical Description
The REU has these physical properties:
Length is 17.6 in. (320 mm)
Height is 7.62 inches (194 mm)
Width is 3.58 inches (90.0 mm)
Weight is 7.75 pounds (35.2 kg).
Functions
The REU uses the ACP selections to connect these signals:
Communication transceiver audio
Navigation receiver audio
Passenger address audio
Service interphone audio
Flight interphone.
Purpose
The control wheel PTT switch gives push-to-talk input for the boom or oxygen mask microphones.
Description and Controls
The control wheel PTT switch is a three position switch. It is on the outboard horn of the captain’s and the first officer’s control wheel. These are the switch positions:
MIC - microphone audio and PTT signals go to the communication system you select
OFF - The ACP PTT switch can key the microphone
INT - microphone audio goes to the flight interphone system (ACP selection is not changed). The switch is spring loaded to the middle OFF position.
General
You use the audio control panel (ACP) to select the audio for headsets and flight interphone speakers. ACPs also select a communication system.
ACP Components
The ACP has these components:
Power supply
Front panel lights and switches
Switching multiplexer
Volume control multiplexer
Select circuits
Emergency circuit.
Power Supply
The ACP gets 15v dc from the REU. The ACP converts this voltage to 12v dc and 5v dc which gives power for electronic circuits.
Master dim and test (MD&T) sends 28v dc or 16v dc to the microphone selector lamps. The airplane electrical system sends 5v ac for panel lighting.
Front Panel Lights and Switches
The ACP has these front panel components:
Microphone select switches with mic select lights
Filter switches
Receiver select switches and volume controls.
The mic select lights get 28v dc or 16v dc from the MD&T circuits. A mic select light turns on when it gets a ground from the electrical interlock programmed logic array(набор,комплект) (PLA) circuit.
When you push the microphone select switch, it sends 5v dc to the PLA. The PLA is an electrical interlock circuit. It makes a 4 bit binary code for the selected switch.
System selection is latched(запирать) into the PLA. The PLA sends the applicable code to the switching multiplexer. The PLA also sends a signal to turn on a receiver volume control when you push the microphone select switch.
Push the receiver volume control to hear audio from the related system. The receiver volume control switch sends a dc voltage from a potentiometer (0 to 12v dc) to the multiplexer. The multiplexer sends this voltage to the REU to set the radio output
volume level. When the audio volume control switch is off, 12v dc goes to the REU and you cannot hear the system audio.
Switching Multiplexer
The switching multiplexer gets these signals:
Microphone select binary code from the PLA circuit
DC voltages from filter switches
DC voltages from the service interphone, PA, and speaker volume controls.
The switching multiplexer sequentially selects the inputs. The data output goes to the REU as a control system data word. This multiplexer operation stops when the volume control multiplexer operates.