Studio Technologies 74 - Manual (Page 42)

Model 74/75 User Guide Issue 2, January 2006
Studio Technologies, Inc. Page 43
for Surround
sources connect to the Model 74. They
then route, via the interface cable, from
the Model 74 to the actual input circuitry,
located in the Model 75.
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 microcontroller;
they do not connect to the Model 75. In-
side 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.