Doug Fleenor Design 123 Руководство пользователя - Страница 4
Просмотреть онлайн или скачать pdf Руководство пользователя для Усилитель Doug Fleenor Design 123. Doug Fleenor Design 123 5 страниц. Dmx512 isolated splitter/amplifier
Печатать страницуTechnical 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 wires they travel on are usually twisted to
insure any 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 standard for lighting control published by the United States Institute For
Theater Technology. The DMX512 standard specifies that the electrical properties of the
signal 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 output goes to the idle state
when no source is connected. A 120 ohm termination resistor is across the data lines to
prevent reflections. On the eleven output model the 120 ohm termination resistor is
absent 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.