Intercom Control Circuit

32-5865-218-24&P

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Intercom Control Circuit. As shown in figure 3-2, the

intercom circuit receives CREW CALL control inputs at connector pins

J7-C, J8-R, and J3-A. When any input is a low (logic 0) signal,

current flows through diode TB1CR1 or TB1CR2 to provide a low to

external system equipment at connector pin J3-C.

In addition, the

following functions occur:

Relay K1 operates when the COCKPIT CREW CALL TRIGGER

(a)

input goes low. Contacts K1-A2 and K1-A1 close to connect the

interphone audio signal at connector pin J7-J to contact B2 of relay

K2. Contacts K1-B2 and K1-B1 close to activate relay K3. Contacts

K3-A2 and K3-A1 connect the flasher lamp control return input at con-

nector pin J7-B to external system equipment at connector pin J7-A.

Relay K2 operates when the CREW CALL TRIG or CREW CALL

(b)

input is low. Contacts K2-A2 and K2-A3 open, and contacts K2-A2 and

K2-A1 close. This connects the interphone audio signal at connector

pin J7-J to external system equipment at connector pins J6-e and J2-L

and removes the terminating resistor TB1R1 from the signal line.

Contacts K2-B2 and K2-B3 open to break the override audio signal path

between contact K1-A1 and connector pins J2-M and J6-g.

(c)

On indicator CCA A3, the output of timer U1A goes high

(logic 1) when any CREW CALL input goes low. The output of timer U1A

The 5 ( 1) Hz output pulse of

resets multivibrator U1B.

multivibrator (U1B) is applied through transistor Q8 to operate relay

K3. Contacts K3-A2 and K3-A1 close to provide the flasher lamp

control output to external system equipment at connector pin J7-A.

The 5 (1) Hz pulse also passes to external system equipment at

connector pin J8-P. After five to seven seconds, the timer output

goes low, multivibrator U1B is inhibited, and relay K3 restores.

Monitor Circuits. As shown in figure 3-3, terminal board

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TB2 and diodes CR5 and CR6 receive transmitter control and plain text

inputs.

Relay TB2K1 is operated by a logic 0 transmitter control

input from external system equipment at connector pin J6-T. The

logic 0 input also causes a low signal through diode TB2CR2 and

connector pin J6-m to external system equipment. When relay TB2K1

operates, contacts A2 and A1 close to connect the PLAIN TEXT FM

signal at connector pin J7-U to diode A3CR5 and to external system

equipment at connector pin J7-G. When the PLAIN TEXT FM signal is a

logic 0, the PLAIN TEXT FM outputs are also low at connector pins

The PLAIN TEXT UHF monitor circuit is a direct link

J8-G and J7-G.

to the system with no separate controls such as relay K1 to affect

its operation. When a logic 0 is input to connector pin J7-H, diode

CR6 is forward biased placing the logic 0 on connector pin J8-L.

When a logic 1 is placed on connector pin J7-H, diode CR6 is reverse

biased and connector pin J8-L becomes a logic 1.

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