Studio Technologies 212 2006 - Manual (Page 32)

Issue 3, July 2006 Model 212 User Guide
Page 32 Studio Technologies, Inc.
P17: Remote switch connections, pin 1
common, pin 2 main output control, pin 3
talkback output audio
.
Pushbutton Backlighting
For special applications, provision has
been made to allow illumination (“back-
lighting”) of the two pushbutton switches.
This may prove useful for applications
where adequate room lighting is not avail-
able. It can also serve in custom Model
212 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 connection to
power both lamps is provided; indepen-
dent access to the lamp connections 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 restric-
tion is that power for the backlighting func-
tion is in addition to the 150 milliamperes
required for normal Model 212 operation.
This should not prove to be a problem
as the lamps only add approximately 40
milliamperes. But it must be taken into
account when determining if the power
source can support the increased load.
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
P15, is located on the Model 212’s main
printed circuit board. It provides access
to, and a means to power, the two lamps.
Pin 1 of the header is connected to the
common point of the Model 212’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
Studio Technologies then adding a “jump-
er” from pin 2 to pin 3 is all that is required
to get things going. A standard 0.1-inch-
center jumper, commonly used on elec-
tronic equipment, is all that is required. A
390 ohm, 1 watt resistor is electronically
in series between the external 24 volt DC
input and pin 3 of the header. When used
with the lamps available from Studio Tech-
nologies, the resistor limits the lamp cur-
rent to approximately 40 mA. This lights
the lamps to a moderate intensity. If a
different type of lamp is installed, its power
source should be connected to pins 1
(common) and 2 (lamps) of the header.
Remote Control Connections
Provision has been made on the Model
212’s printed circuit board assembly to
allow external switches or contact closures
to control the main output and talkback
output functions. A 3-position header, la-
beled P17, provides access to the circuitry
associated with the functions. Pin 1 of the