Studio Technologies 240 - Manual (Page 12)

Issue 1, August 2013 Model 240 User Guide
Page 12 Studio Technologies, Inc.
Line inputs that are going to be assigned as
main output sources should be connected
only on the Model 240 being designated
as the primary unit. Otherwise signals will
“clash” on the combined main audio out-
puts. An intercom circuit would have to be
connected to both Model 240 units, and
configured identically, for correct operation
to take place.
An RS-485 data bus links the microcon-
troller integrated circuits on the two units
and conveys button status information.
Only one pair of wires for the data bus is
required. An installer-provided connector
is necessary. Please refer to the Technical
Notes section of this guide for connection
details.
External Power Input
An external source of 24 volt DC power can
be connected to the Model 240 by way of
a 2.1 x 5.5 mm coaxial power jack which
is located on the back panel of the unit.
The center pin of the jack is the positive
(+) connection. While the requirement for
the external source is nominally 24 volts,
correct operation will take place over a 20
to 30 volt range. The Model 240 requires
125
milliamperes at 24 volts DC for correct
operation. Included with each Model 240
is a 24 volt DC external power supply. The
power supply’s DC output cable has been
terminated with a Switchcraft® S760K co-
axial power plug. This “locking” type of plug
correctly mates with the Model 240’s 24 Vdc
input jack. The locking feature is important,
allowing the external power source to be
securely attached to the Model 240.
As previously discussed in this guide, an
intercom circuit connected to the Model 240
can serve as the unit’s power source. For
redundancy, the intercom circuit and the ex-
ternal 24 volt DC source can be connected
at the same time. If one of them becomes
inoperative the remaining source will pro-
vide power for the Model 240.
The Model 240’s circuitry establishes the
priority in which the unit draws its operat-
ing power. If an external source of 24 volt
DC power is connected, it will always serve
as the primary source. This minimizes the
impact that the unit’s power draw could
have on a connected intercom circuit. If no
external source of 24 volt DC is connected
then power will be drawn from the intercom
circuit.
Pushbutton Labeling
The four pushbutton switches used in the
Model 240 were selected for several rea-
sons. Foremost was the fact that they are
highly reliable, using gold-plated contacts
for long life in less-than-ideal environ-
ments. A second reason was that apply-
ing customized labels to the button caps
would be very simple. Labels, text printed
on clear material, can be placed under the
clear lens that is part of the button cap.
And with the integrated white LED back-
lighting the label text will be highly legible.
From the factory the four lenses in the
button caps are not directly labeled. This
is because there are simply too many
possible uses for the Model 240 to allow
“default” labels to be meaningful. Text on
the graphics label on the Model 240’s front
panel does provide a simple indication of
the button positions, showing 1, 2, 3, and
4. But it’s expected that some applications
may benefit from more-specific labels
being added to the button caps.
As a “head start” for some applications, a
clear sheet with a number of commonly
used button designations printed on it is in-
cluded in the shipping carton. These were
created at the factory using a standard