Biamp LTR User Manual
Page 161
Component Objects
Logic Box behavior can be altered using
. Please refer to
the 'Installation Guide' (included with controls), or see
for more information. External controls must be identified (see
) and associated with their corresponding
component blocks within the layout (see
Up to 20 logic inputs are availble on the Logic Box. Logic inputs allow remote control of Audia®
via external circuits such as switches, relays, and logic outputs from other devices. When
nothing is connected to a logic input, an internal pull-up resistor keeps it at a ‘high’ state (+5.0
VDC). The logic input is activated when its input goes ‘low’ (less than +0.8 VDC), and is de-
activated when its input goes ‘high’ (greater than +2.0 VDC). A logic input can be controlled in
one of three ways: 1) Using an ‘open-collector’ or ‘open-drain’ logic output from an external
device to short the logic input to ground. 2) Using a switch, relay, or other contact-closure to
short the logic input to ground. 3) Using an active 5V TTL output driver circuit (such as from a
third-party controller) to actively drive the logic input to a ‘high’ or ‘low’ state. Multiple contact-
closures or ‘open-collector’/’open-drain’ logic outputs may be wired in parallel to a single logic
input (see diagram below). Open-collector or open-drain logic outputs and contact-closures
should be rated for at least 5 Volts / 1mA operation. Active output driver circuits should not
exceed a signal range of 0~5 Volts DC, and should have a minimum pulse width of 10 milli-
seconds. The logic input impedance is approximately 10 Kohms.
The Logic Box provides up to 20 logic outputs. Logic outputs can be used to control relays and
indicators or to drive logic inputs of other devices. The Logic Box logic outputs are ‘open
collector’ with an internal pull-up. Each logic output is an NPN transistor with the collector being
the output and the emitter being ground (see diagram below). When a logic output is turned on,
the transistor provides a path for DC current to flow, lowering the output voltage to below 0.8V.
When a logic output is turned off, the internal pull-up resistor raises the output voltage to near
5V, depending on the output current. To activate external relays or indicators, an external power
supply must be used (see diagram below). The logic output transistors are rated up to a
maximum of 40 VDC and 500 mA per output (24 volt relay coils maximum). However, +12 Volts
DC is sufficient power for most applications. When using the logic outputs to control relays,
protection diodes must be used to suppress high voltage transients that are generated when the
relays turn off (see diagram below).
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