Blizzard Lighting RokPix (Rev A) - Manual (Page 6)

Page 6
R
okPix Manual R
ev
. A
© 2013 Blizzard Lighting, LL
C
Figure 1: The RokPix™ Pin-Up Picture
High P
ower 4-in-1
Quad Color LEDs
Hea
vy
-Duty Cast
Aluminum Enclosure
Dual Mounting Y
o
kes &
Adjustment/Locking Knobs
Figure 2: The Rear Connections
AC P
ower Out
DMX In
DMX Out
Menu Buttons
AC P
ower In
LED Displa
y
Page 15
R
okPix Manual R
ev
. A
© 2013 Blizzard Lighting, LL
C
5. APPENDIX
A Quick Lesson On DMX DMX (aka DMX
-512) w
as created in 1986 by the United States Institute for Theatre
Technology (USIT
T) as a standardiz
ed method for connecting lighting consoles to lighting
dimmer modules. It w
as revised in 1990 and again in 2000 to allow more
fl
exibility
. The
Entertainment Services and T
echnology Association (EST
A) has since assumed control o
ver
the DMX512 standard. It has also been appro
ved and recogniz
ed for ANSI standard clas-
si
fi cation.
DMX co
vers (and is an abbreviation for) Digital MultipleX
ed signals. It is the most common
communications standard used by lighting and related stage equipment. DMX pro
vides up to 512 control “channels” per data link. Each of these channels w
as origi-
nally intended to control lamp dimmer lev
els. Y
ou can think of it as 512 faders on a lighting
console, connected to 512 light bulbs. Each slider
’s
position is sent o
ver the data link as an
8-bit number ha
ving a v
alue between 0 and 255. The v
alue 0 corresponds to the light bulb
being completely off while 255 corresponds to the light bulb being fully on. DMX data is tr
ansmitted at 250,000 bits per second using the RS-485 tr
ansmission stan-
dard o
ver two wires. As with microphone cables, a grounded cable shield is used to prev
ent
interference with other signals. There are
fi
ve
pins on a DMX connector: a wire for ground (cable shield), two wires for
“Primary” communication which goes from a DMX source to a DMX receiv
er
, and two wires
for a “Secondary” communication which goes from a DMX receiv
er back to a DMX source.
Gener
ally
, the “Secondary” channel is not used so data
fl
ows only from sources to receiv
-
ers. Hence, most of us are most familiar with DMX
-512 as being emplo
yer o
ver typical
3-pin “mic cables,
” although this does not conform to the de
fi ned
standard.
DMX is connected using a daisy
-chain con
fi
gur
ation where the source connects to the input
of the
fi
rst device, the output of the
fi
rst device connects to the input of the next device,
and so on. The standard allows for up to 32 devices on a single DMX link. Each receiving device typically has a means for setting the “starting channel number
” that
it will respond to
. F
or example, if two 6-channel
fi
xtures are used, the
fi rst
fi xture
might
be set to start at channel 1 so it would respond to DMX channels 1 through 6, and the next fi
xture would be set to start at channel 7 so it would respond to channels 7 through 12.
The greatest strength of the DMX communications protocol is that it is v
ery simple and
robust. It in
volv
es tr
ansmitting a reset condition (indicating the start of a new “pack
et
”),
a start code, and up to 512 bytes of data. Data pack
ets are tr
ansmitted continuously
. As
soon as one pack
et is
fi
nished, another can begin with no dela
y if desired (usually another
follows within 1 ms). If nothing is changing (i.e. no lamp lev
els change) the same data will
be sent out o
ver and o
ver again. This is a great feature of DMX -- if for some reason the
data is not interpreted the
fi
rst time around, it will be re-sent shortly
.
Not all 512 channels need to be output per pack
et, and in fact, it is v
ery uncommon to
fi nd
all 512 used. The fewer channels are used, the higher the “refresh” r
ate. It is possible to
get DMX refreshes at around 1000 times per second if only 24 channels are being tr
ans-
mitted. If all 512 channels are being tr
ansmitted, the refresh r
ate is around 44 times per
second. In summary
, since its design and ev
olution in the 1980’
s DMX has become the standard
for lighting control. It is
fl
exible, robust, and scalable, and its ability to control ev
erything
from dimmer packs to mo
ving lights to foggers to lasers mak
es it an indispensable tool for
an
y lighting designer or lighting performer
.