Doug Fleenor Design 1211 User Manual

DMX512 ISOLATED SPLITTER/AMPLIFIER

OWNERS MANUAL

Doug Fleenor Design

396 Corbett Canyon Road

Arroyo Grande, CA 93420

[phone]

revision 1.3
August, 1999

PRODUCT DESCRIPTION

The Splitter/Amplifier provides between one and eleven DMX512 outputs from a single DMX512
input. The outputs are electrically isolated from the input and from each other by 2500 volt optical
couplers.

All models of our Splitter/Amplifier boost the signal as well as isolate it. I nput levels as low as 0.2
volts are transmitted at full EIA-485 levels (about 4.5 volts).

The splitters allow the DMX signal to be split without the possibility of reflections from one sig nal
path interfering with the signal to a device on a different path. By isolating each output, electrical
noise and hazardous voltages on one output are prevented from affecting (or damaging) devices on
the input or another output.

Common uses for the Splitter/Amplifier include:
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Boosting the signal level on long control runs (greater than 500 feet)

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Splitting the signal to multiple dimmer locations

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Splitting the signal betw een dimm ers and other D MX devices (color changers, moving lights, etc.)
Isolating two or three dimmer packs from each other.

Although this product was designed for the digital multiplex lighting control standard DMX512, the
units use standard EIA-485 components. They can be used to split and isolate any single-drop uni­directional EIA-422 or EIA-485 line up to the rated data rate of 250 Kb/s.

SETUP AND CONNECTIONS

Plug the splitter's line cord into a grounded electrical outlet. The splitter requires between 100 and
120 volts, 50 or 60 hert z. It requires less than 1/10 amp (12 W atts). It should be grounded for
maximum electrical noise isolation and safety. The earth ground is connected only to the chassis.
All circuitry is isolated from the chassis and the power cord's ground pin.

Plug the console or other DMX source into the Splitter/Amplifier's input connector. Connect the
output(s) of the unit to the dimmers or other DMX receivers.

The splitter is normally provided with the connectors specified for DMX512:

Input = 5 pin male "XLR" style Output = 5 pin female "XLR" style

The signals on each pin are:

1 = Common
2 = Data ­3 = Data +
4 = No Connection
5 = No Connection

The unit may also be ordered with non-standard connectors such as 3 pin "XLR" style.

Note that pin 1 is common in name only. All commons are electrically isolated from each other.

OPERATION

The DMX512 splitter has no operator controls; it is fully automatic. It should be left plugged in at
all times for automatic operation. When a DMX signal is applied to the input, it is processed by the
receive circuit, isolated by the opt ica l couplers, and retransmitted by the driver circuits. All this
takes less than 1/10,000,000 of a second.

When no DMX input is present, the outputs are placed in an idle condition. This condition is
defined in the DMX512 specification as Data+ line high and Data- line low.

Two indicators are provided on the front panel of the splitter. The red POWER indicator is
illuminated whenever the power cord is plugged into a live outlet. The green SIGNAL indicator is
illuminated whenever the Data+ and Data- lines leave their idle state. Note tha t the signal indicator
does not necessarily indicate a valid signal, only that the line is not idle.

The signal indicator will change intensities as the leve ls sent to the outputs are varied. I n some cases
the signal indicator may be quite dim even though data is being received. The indicator will be at
its lowest intensity when all dimmers are being sent to full. Try sending all dimmers to zero then
look at the indicator.

LINE TERMINATION

The input of the one, three, and five output models are terminated with 120 ohm 1/2 watt resistors.
This is the proper input termination for DMX512 lines. Since these models do not provide pass­through of the input DMX signal, the unit is always the last device on the line. (These unit may be
customized with a feed through, in which case it must be terminated.)

The input of the eleven output model is not terminated. To properly terminate the DMX input, a 120
ohm termination plug must be plugged into on the pass-through connector.

It is recommended that all control runs be terminated. The most important place to use termination
is on a control run where the signal daisy chains from a source (console, isolator, splitter, etc.) to
several receivers (dimmers, color scrollers, etc.) with hundreds of feet separating t he receivers. What
happens in such a case is that the signal seen by the receivers is a combination of the correct signal
(sent by the console) and a delayed version of that signal which is reflected from the end of the cable.
The longer the cable, and the more devices on the cable, the more the reflected signal tends to distort
the initial signal. The cure (in theory) is to absorb the signal at the end of the cable so that none is
reflected back up the line.

To terminate a typical control run place a 120 Ohm resistor between the Data+ (pin

3) and Data- (pin 2) lines at the last receiver on the line.

Unused outputs on a DMX512 splitter do not need to be terminated.

TECHNICAL DETAILS

DMX512 uses a "differential" digital signal. A differential signal is a pair of signals which are
inverse from one another. That is, when one is high, the other is low. Differential signals are
common in both analog processing (balanced microphone cables) and digital processing (digital
communications such as EIA-485). Differential signals are used to reduce the effect of electrical
noise on long cable runs. When a differential signal is processed by the receiving circuit
(microphone pre-amp or EIA-485 receiver for example) the noise can be eliminated but the signal
remains.

Differential signals always travel in pairs; the wire s they tr avel on are usually twisted to insure an y
noise picked up is of equal magnitude on both wires. The noise must be of equal magnitude on each
wire so that the receiving circuit can effectively subtract the noise and leave the signal. The pairs
of signals are usually denoted by a plus (+) sign on the normal, or "hot", or "true" line and by a minus
(-) sign on the inverted, or "return", or "complement" line. The differential signals on the splitter are
Data+ and Data-.

DMX512 is a stan dard for lighting control published by the United States Institute For Theater
Technology. The DMX512 standard specifies that the electrical properties of the sig nal comply with
a standard published by the Electronic Industries Association, EIA-485 (or RS-485). Many
manufacturers make integrated circuits that meet the input and output specification of EIA-485. The
DMX512 Isolated Splitter/Amplifier uses a "75179" as the receiver and "75176's" as transmitters;
both of which were designed specifically to meet EIA-485. Between these circuits is a "6N137"
optical coupler which isolates the two circuits using a beam of light passing through a layer of glass.
The "6N137" is rated to a maximum speed of 10 million bits-per-second and provides isolation to
2500 Volts.

Since the receiver and transmitters all require power, and they must be isolated, multiple 5 volt
power supplies are included. Transformers, each with two secondaries, steps the 120 volt line down
to 10 volts. A 1N4004 diode converts the 10 volts AC to 14 volts DC. A 330 uF capacitor filters
the DC and a 7805 regulates it down to 5 volts.

Resistors are included on the input of the splitter. The one, three, and five output models have 1K
pull up/down resistors on the input to insure the out put goe s to the idle state when no source is
connected. A 120 ohm termination resistor is across the data lin e s t o p r event reflections. On the
eleven output model the 120 ohm termination resistor i s ab sent since a pass through connector is
provided to loop on to additional splitters. Also, the eleven output model uses 22K pull up/down
resistors so as to not load the line.

TROUBLESHOOTING

We hope your DMX512 Isolated Splitter/Amplifier never needs service. If it does, the information
presented here may be of assistance.

Access to the inside of the unit is accomplished by removing the top cover.

The input fuse is a 1/2 amp 3AG fast blow fuse.

The output drivers are 75176B devices. A 75176A will work but is not as rugged.

The input receiver is a 75179B.

The optical isolator is a 6N137.

Schematics are available from Doug Fleenor Design.

WARRANTY

Products manufactured by Doug Fleenor Design carry a five year parts and labor warranty against
manufacturing defects. It is the customer's responsibility to return the product to Doug Fleenor
Design (at the customer's expense). Doug Fleenor Design will repair the unit and return it to the
customer (at Doug Fleenor Design's expense). If a trip is necessary to the customer's site to solve
a problem, the expenses of the trip must be paid by the customer.

Note that this warranty is against Manufacturing Defects. I t does not include damage due to misuse
or abuse. Most non-warranty repairs are made for a fixed $30.00 fee.