Studio Technologies 220 2004 - Manual (Page 35)

Issue 2, August 2004 Model 220 User Guide
Page 36 Studio Technologies, Inc.
P14: Line input 1, pin 1 common, pin 2
high, pin 3 low.
P15: Line input 2, pin 1 common, pin 2
high, pin 3 low.
Additional functions can be accessed
using these 3-position headers:
P9: Auxiliary relay contact B, pin 1
normally closed, pin 2 common, pin 3
normally open.
P10: Auxiliary relay contact A, pin 1
normally closed, pin 2 common, pin 3
normally open.
P17: Remote switch connections, pin 1
common, pin 2 talkback 1 button, pin 3
talkback 2 button.
P18: Remote switch connections, pin 1
common, pin 2 main out button, pin 3
auxiliary (currently not supported in
software).
P20: Pushbutton backlighting, pin 1
common, pin 2 button lamps, pin 3
current limited 24 volts from external
24 volt DC input.
Pushbutton Backlighting
For special applications, provision
has been made to allow illumination
(“backlighting”) of the three pushbutton
switches. This may prove useful for ap-
plications where adequate room lighting is
not available. It can also serve in custom
Model 220 configurations. Note that this is
an advanced feature, intended only to be
implemented by a qualified technician.
From the outset several limitations must
be discussed. The first is that button
backlighting is not intended to serve
tally applications. (A common connec-
tion to power all three lamps is provided;
independent access to the lamp connec-
tions on each button is not provided.) It
is strictly intended to provide a moderate
amount of illumination to the button’s clear
lens and associated labeling. The second
restriction is that power for the backlight-
ing function cannot be provided by the IFB
input—there is simply not enough cur-
rent available from a typical IFB circuit to
power the Model 220 and light the lamps.
However, power from the external 24 volt
DC source can be used. This requires that
this power source be connected whenever
backlighting is desired.
From the factory, lamps (“bulbs”) are not
installed in the pushbutton housings.
They are pluggable T-1 bi-pin type and
are simple to install. The mating socket is
accessed by removing the button’s lens
caps, graphic label, and back frosted
lens. Compatible incandescent lamps with
a nominal rating of 18 volts, 28 mA are
available from Studio Technologies (part
number 12030). Bulbs with other nominal
voltages should also be available from
electronics parts vendors. While compat-
ible LED-based lamps are probably also
available, incandescent lamps, when pow-
ered below their rated current and voltage,
can provide extremely long and reliable
operation.
A 3-position header connector, labeled
P20, is located on the Model 220’s main
printed circuit board. It provides access
to, and a means to power, the three lamps.
Pin 1 of the header is connected to the
common point of the Model 220’s circuitry,
which is also connected to one contact
on both lamps. Pin 2 of the header is con-
nected to the other contact on both lamps.
Pin 3 is connected, by means of a current
limiting resistor, to the external 24 volt DC
source. If lamps were obtained from Stu-
dio Technologies then adding a “jumper”
from pin 2 to pin 3 is all that is required