User Guide

Model฀74/75฀User฀Guide฀ Issue฀3,฀November฀2016฀
Studio฀Technologies,฀Inc.฀ Page฀43
for Surround
It฀should฀be฀noted฀that฀the฀infrared฀(IR)฀
remote฀talkback฀circuit฀“tags฀along”฀with฀
the฀hard-wired฀remote฀talkback฀input.฀An฀
IR฀receiver฀module฀connects฀via฀input฀
circuitry฀to฀the฀Model฀74’s฀microcontroller฀
integrated฀circuit.฀Under฀software฀control฀
IR-generated฀requests฀for฀talkback฀are฀
decoded.฀A฀logic฀output฀pin฀on฀the฀mi-
crocontroller฀goes฀to฀logic฀high฀(+5฀volts฀
DC)฀whenever฀talkback฀is฀detected.฀This฀
signal฀drives฀the฀input฀of฀an฀optocoupler฀
integrated฀circuit.฀The฀optocoupler’s฀output฀
transistor฀is฀connected฀directly฀across฀pin฀
7฀(remote฀talkback)฀and฀pin฀9฀(ground)฀on฀
the฀two฀9-pin฀D-subminiature฀connectors.฀
In฀this฀way฀the฀IR฀talkback฀input฀is฀“OR’d”฀
(connected฀in฀parallel)฀with฀the฀hard-wired฀
remote฀talkback฀input.฀The฀signal฀reaches฀
the฀Model฀75฀Control฀Console฀where฀it฀
performs฀the฀talkback฀function.฀The฀Model฀
75฀doesn’t฀have฀the฀logic฀to฀recognize฀a฀
remote฀talkback฀signal฀that฀is฀generated฀by฀
a฀hard-wired฀connection฀or฀a฀IR฀request.
Spare฀Remote฀Control฀Inputs
Figure฀10฀lists฀two฀spare฀(unused)฀remote฀
control฀inputs.฀These฀inputs฀are฀provided฀
for฀future฀special฀applications.฀It’s฀inter-
esting฀to฀note฀that฀they฀are฀quite฀unlike฀
the฀four฀hard-wired฀remote฀control฀inputs.฀
Inside฀the฀Model฀74,฀the฀four฀hard-wired฀
remote฀control฀inputs฀are฀directly฀routed฀
to฀the฀connector฀that฀links฀to฀the฀Model฀
75฀Control฀Console.฀The฀microcontroller฀
in฀the฀Model฀75฀monitors฀and฀acts฀upon฀
those฀four฀signals.฀The฀two฀spare฀inputs฀
stay฀within฀the฀Model฀74,฀connecting฀to฀
input฀ports฀on฀the฀Model฀74’s฀microcon-
troller;฀they฀do฀not฀connect฀to฀the฀Model฀
75.฀Inside฀the฀Model฀74฀these฀spare฀inputs฀
are฀“pulled”฀to฀logic฀high฀(5฀volts)฀and฀ESD-
protected฀prior฀to฀connecting฀to฀the฀Model฀
74’s฀microcontrollers.