Specifications

12
LOGIC OUTPUTS
The VRAM provides eight logic outputs on a rear panel 9-pin Subminiature D (male) connector. Logic Outputs can be used to control
external switching circuits (such as relays) for speakers, cameras, indicators, etc. The VRAM Logic Outputs are most often used, in
conjunction with external relays, to turn off specific speakers when nearby microphones are active (reducing feedback problems). For
example, if a speaker is located directly above microphone #1, the Logic Output for Channel 1 of the VRAM can be used to turn off that
speaker relay when microphone #1 is active (see diagram on next page). The Logic Outputs can also be combined (wired in parallel) to
control a single circuit. For example, a speaker relay could be turned off when either microphone #1 or microphone #2 is active. In
addition to speaker relays, the VRAM Logic Outputs may be used to control external indicator lights (see diagram on next page). Another
common application for Logic Outputs is to control video cameras. Different cameras could be activated depending upon which
microphone (or group of microphones) is currently active. Cameras can be selected (using a video switcher such as a VSX41) and/or
camera presets may be triggered (using a ‘pan/tilt/zoom’ camera system). The VRAM Logic Outputs may also be used in conjunction with
the VRAM Logic Inputs to perform such functions as ‘automatic priority’, which allows a microphone (or group of microphones) to be muted
whenever specific ‘priority’ microphones are active (see diagram on next page). The Logic Output for the ‘priority’ microphone is wired to a
Logic Input which is defined to mute the other microphones (see Setup on pg. 8). A similar approach is useful for ‘page-over-music’
applications. However, in this case the Logic Outputs from multiple ‘paging’ microphones are wired to a Logic Input which is defined to
mute the music channel. Multi-level priority schemes are also possible, but require the use of multiple Logic Inputs and a diode matrix.
These ‘priority’ applications require that Logic Inputs do not follow Designated Mic On / Last Mic Hold (see Setup on pg. 6). Of course,
manual muting of microphones via external switches is also possible (see Logic Inputs on pg. 10).
The VRAM Logic Outputs are ‘open collector’ outputs. Each Logic Output is an NPN transistor with the collector being the output and the
emitter being ground (see diagram on next page). When a Logic Output is turned on, the transistor provides a path for DC current to flow.
The Logic Outputs do not provide any voltage or current. They act only as switches (with a common ground return). To activate external
relays, an external power supply must be used (see diagram on next page). The Logic Output transistors are rated up to a maximum of 24
VDC and 50 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 on next page). Any of the 1N4004 family of diodes (1N4001, 1N4002, 1N4003, 1N4004, 1N4005, 1N4006, 1N4007,
or equivalent) will provide proper protection. A 12 Volt Power Supply (#909-0011-00), 12 Volt Relays (#310-0059-00), and 1N4004 Diodes
(#190-0003-09) are available from Biamp Systems. When a Logic Output goes on, the associated relay may be wired to perform on, off, or
’A/B’ switching functions. To use logic ‘on’ to turn on (or activate) a device, wire across the ‘normally open’ relay contacts, in series with
the device (or control voltage source). To use logic ‘on’ to select between ‘A’ or ‘B’ signals (inputs or outputs), wire one signal to the
‘normally closed’ relay terminal and the other signal to the ‘normally open’ relay terminal, with the common relay terminal providing the feed
(input or output).
logic out pin number
channel 1
channel 2
channel 3
channel 4
channel 5
pin #1
pin #2
pin #3
pin #4
pin #5
pin #6
pin #7
pin #8
pin #9
channel 6
channel 7
channel 8
ground
9-pin cable-end
5
9
8
7
6
1
2
3
4
logic
outputs
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