StudioTech 233 manual Remote Control/Tally Connections, P18

configurations. Note that this is an ad- vanced feature, intended only to be implemented by a qualified technician.

From the outset several limitations must be discussed. The first is that button back- lighting is not intended to serve tally appli- cations. (A common connection to power all three lamps is provided; independent access to the lamp connections on each button is not provided.) It is strictly in- tended to provide a moderate amount of illumination to the button’s lens and as- sociated labeling. The second restriction is that power for the backlighting function cannot be provided by an intercom line— it was felt that there may not be enough current available from this source to power both the Model 233 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 P14, is located on the Model 233’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 233’s circuitry, which is also connected to one contact on all the lamps. Pin 2 of the header is con- nected to the other contact on the 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 to get things going. A standard 0.1-inch- center jumper, commonly used on elec- tronic equipment, is all that is required. A 200 ohm, 2 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 65 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/Tally

Connections

Provision has been made on the Model 233’s printed circuit board assembly to allow external switches or contact closures to control the main output and talkback button functions. In addition, a DC “tally” output signal provides an indication of the status of the main output. Two 3-position headers provide access to the circuitry associated with these functions.

P18:

Pin 1 is connected to the common point of the Model 233’s circuitry. Pin 2 is con- nected to the circuitry associated with the talkback 1 button. Pin 3 is connected to the circuitry associated with the talkback 2 button.

Issue 1, September 2007	Model 233 User Guide
Page 42	Studio Technologies, Inc.