Studio Technologies 76B 2008 - Manual (Page 12)

Issue 1, July 2008 Model 76B/77B User Guide
Page 12 Studio Technologies, Inc.
for Surround
or oscilloscope to confi rm that the metada-
ta source is actually on the expected pins
of the source connector prior to connecting
it to the Model 76B.
Remote Control Inputs
Support is provided for three remote
control input functions: remote mute all,
remote dim, and remote auxiliary out-
put on/off. The inputs use logic gates,
“pulled up” to +5 volts DC by way of resis-
tors, which are active whenever they are
brought to their logic low state. Inputs of
this type are commonly referred to as GPI
inputs. While the input circuitry is protected
from over-current and static (ESD) dis-
charge, care should be taken to prevent
nasty signals from reaching them. The
inputs are active only when held in the low
state; they can’t be confi gured to change
state (“latch”) in response to a logic pulse.
The same 9-pin D-subminiature connector
used for the metadata input is also used
for the remote control inputs. Refer to
Figure 5 for the exact connection details.
Note that pin 4 (remote input common)
connects to the Model 76B’s internal circuit
common connection as well as the Model
76B’s chassis and mains earth connec-
tions. Figure 5 also shows one spare
remote control input (pin 9). This is pro-
vided for future applications and should
remain unconnected.
Connecting the Model 76B
to the Model 77B
A 9-pin female D-subminiature connector,
labeled To/From Control Console, is pro-
vided on the back panel of the Model 76B
Central Controller. This is used to interface
the unit with Model 77B Control Consoles.
A 9-pin female D-sub connector, labeled
To/From Central Controller, is provided
on the back panel of each Model 77B
Control Console. A cable with 9-pin male
D-sub connectors on each end is used to
interconnect the Model 76B with the Model
77B units. A 20-foot (6.1-meter) cable is
included in the shipping carton. The cable
implements all nine connector pins in a
one-to-one manner.
Should an interconnecting cable of a differ-
ent length be required there’s no problem
for one to be fabricated and used. While it
can be wired in a one-to-one fashion cov-
ering all nine pins, a minimum of only four
connections are required: pin 1 (data+),
pin 6 (data–), pin 4 (DC+), and pin 9
(DC–). The Model 76B’s connector pin-out
scheme was designed to allow creation of
an interconnecting cable which uses com-
monly available 2-pair audio cable. This
cable, consisting of two twisted pairs each
with an individual shield, is typically sleek,
fl exible, and available in many colors. One
pair and shield can be used for the data
connections while the other pair and shield
can be used for the DC connections. This
implementation has the advantages of
providing a shield for the data path and
a more robust common connection (two
conductors including the shield) for the DC
power circuit. Refer to Figure 6 for details.
A few simple calculations are required to
determine the maximum cable length when
connecting a Model 77B to a Model 76B.
The differential transmission scheme used
by the system’s RS-485 interface makes
an interconnection in excess of 1000 feet
(300+ meters) easily possible. The limiting
factor is typically the ability of the wiring to
pass the DC power supplied by the Model
76B to the Model 77B. The Model 76B sup-
plies 12 volt DC nominal with a maximum
current of 200 milliamperes.