Control/Dimming Ethernet hub as DMX512 opto-splitter?

[DMXpro]

Hi,
I am in the market for an inexpensive opto-splitter. However, I want to experiment: I had an idea to essentially make one for no cost, as I have access to all materials for free. The idea would be to use an Ethernet hub as the splitter, and adapt RJ45 to 5 pin XLR. Is this feasible? I figured it should work since hubs do not "manage" the data like switches do; they'll just send along whatever they receive, so there's no chance of a failure due to the lack of recognition of DMX512 data as opposed to Ethernet. (And before you refer me to the $100 Enttec opto.....I've already seen it . just wondering if there's an even easier way to do it.)
Thanks!

 

[tk2k]

DMX and standard ethernet are not electrically compatible! You've seen DMX over Cat5, which works perfectly, however the routing hradware is specifically designed to handle DMX over Cat5. A standard TCP/IP router is NOT electrically compatible with DMX over CAT5.

Also, switches are not isolated.

 

[cpf]

If it worked (which I highly doubt it would), it would not be isolated.

 

[DMXpro]

Well the least I can do is experiment, I guess. I know isolation is to protect the circuitry from voltage spikes (right?), but is it absolutely required?

 

[Wood4321]

Feel free to experiment, however, I am 100% sure you are not going to have any success.
An ethernet hub cannot split dmx signal. (unless you convert to art net.)
The 2 types of signal just are not compatible.

 

[Footer]

Well the least I can do is experiment, I guess. I know isolation is to protect the circuitry from voltage spikes (right?), but is it absolutely required?

It won't work. First, if you managed to find a hub in this day and age I will be amazed. True hubs have not been made for years.

Your switch is not going to be able to read the serial signal coming in. It's not going to have the right frame rate and headers to go anywhere. You would be better off just buying some wire nuts. You'll get about the same result.... Neither will work.

Sent from my Galaxy Nexus using Tapatalk 2

 

[DMXpro]

It won't work. First, if you managed to find a hub in this day and age I will be amazed. True hubs have not been made for years.

I have a few. That's how.

 

[derekleffew]

Well the least I can do is experiment, I guess. ...

No, the least you can do is buy or build the proper EIA-485 distribution device.

Isolation is to prevent a spike from input to output, as well as to prevent fault propagation from one output to the others.

From Pathway Connectivity Inc. - Cat5 Pinout for DMX :

This chart is intended for DMX512 cabling only - NOT DMX-over-Ethernet cabling. Great care must be taken to prevent the accidental connection of DMX equipment to non-DMX equipment. The connection of DMX equipment to non-DMX equipment such as Ethernet switches or telephone equipment may result in serious equipment damage and/or personal injury, as pins 4 and 5 may carry voltages of up to 48VDC or greater.

----

... You've seen DMX over Cat5, which works perfectly, however the routing hradware is specifically designed to handle DMX over Cat5. ...

There's often confusion between DMX-over-CAT5 and DMX-over-Enternet. Blame those who use the terms CAT5 and Ethernet interchangeably.
-----

... You would be better off just buying some wire nuts. You'll get about the same result.... Neither will work.

Actually, that's not true. Wire nut s will work better than a network hub.
http://www.controlbooth.com/forums/lighting-electrics/23863-diy-dmx-splitter.html
http://www.controlbooth.com/forums/lighting-electrics/13098-splitting-dmx-line.html

 

[DMXpro]

So basically, the hub doesn't speak the same "language", so it doesn't work for DMX512?

 

[DuckJordan]

The hub is looking for a different signal, it will then reproduce said signal. If its getting a signal it doesn't understand it will attempt its version of the signal (generally causing havoc). Its like asking a Spanish interpreter to interpret Russian. They may get a few things right but most of it will be incomprehensible.

 

[cpf]

So basically, the hub doesn't speak the same "language", so it doesn't work for DMX512?

Pretty much. The Ethernet physical layer defines the electrical protocol used to transmit data over the wire - and it's completely incompatible with DMX. A switch expecting "Ethernet" (1XXXBASE...) but instead getting DMX will probably just ignore it.

 

[Footer]

The hub is looking for a different signal, it will then reproduce said signal. If its getting a signal it doesn't understand it will attempt its version of the signal (generally causing havoc). Its like asking a Spanish interpreter to interpret Russian. They may get a few things right but most of it will be incomprehensible.

Also without full duplex communication, a hub or switch should do nothing.

Sent from my Galaxy Nexus using Tapatalk 2

 

[ziggy]

This will not work on so many levels.

To run thru some of the first issues..

DMX is a balanced RS485 signal that is 3 to 5 volts in amplitude. The driver and receiver are always connected to the line although these circuits may be isolated from ground. No signals are generated to show if a connection is wired or not. It is a logic signal that has no signal processing done to reduce harmonics. It is also a non return to zero encoding, ie if the data for a channel is on full ( hex 0FF or binary 111111) then a DMX line will be high for all these bit times. Data for DMX is 250Kb per second, by modern standards this is very slow but it does have the advantage that the clock for sending and receiving data does not have to be in sync. Each byte with added start and stop bits will resync and the amount of drift over this time is small enough for no errors to occur.


Network BaseT again is a balanced signal but is always isolated either inductively if external to equipment or capacitively if internal (on backplanes for example). To meet EMC requirements signal amplitude is in the 100's of millivolts and the waveform shape is carefully controlled to reduce harmonics. Depending on the speed 10 / 100 /1000 / 10G the encoding of the data varies but they all have one thing in common that the data has a high and low on each bit or symbol. This allows the clock to be recovered from the data to allow both ends to stay in sync.
Modern systems will go thru a negotiate sequence when a cable is plugged in to determine what speed and mode to run in as well as sort out cable pairs for transmit and receive. Once the link is established groups of pulses are put on the line to keep the connection in place when no data is being carried. In the days of 10BaseT ( and hubs) the link was kept alive by sending a single 100nSec pulse on a regular basis. Without this the connection would be dropped.

Both hubs and switches check the framing of data as it arrives....DMX will fail to get recognised as a valid packet and would be dropped.


George McDuff
ChamSys

 

[n1ist]

As many have mentioned, there's no way for it to work (short of removing the board in the hub and replacing it with a DMX splitter)
- The pinout is different
- The voltages are different
- The signals are different
- The timing is different
- The data format is different

/mike

 

[JD]

As many have mentioned, there's no way for it to work (short of removing the board in the hub and replacing it with a DMX splitter)
- The pinout is different
- The voltages are different
- The signals are different
- The timing is different
- The data format is different

/mike

I'll add one more:
- The topology is different.

DMX is a backbone/daisy chain topology, where the sending source is low impedance, but the receivers are high impedance. Ultimately, the chain ends in a terminator. Thus, up to 32 devices can be in the chain. Straight DMX is not bi-directional.

Ethernet is a "star" topology, where each sender terminates into one receiver. In each case, two of the pairs are used, one in each direction to archive bidirectional communication. In addition, many "hubs" isolate using a small transformer. The frequency of the signal is much higher. The larger, lower frequency of DMX signal will saturate this transformer, loading the line down, so even a "passive" hub with no processing would not work with DMX.

 

[tk2k]

So basically, the hub doesn't speak the same "language", so it doesn't work for DMX512?

Sorry to be so blunt but did you even read my post? Electrically incompatible. Aka it'll short out either your console or hub

 

[tdrga]

I'm surprised nobody has asked if they can use a power strip as a DMX splitter.

All you have to do is adapt the DMX 3-pin to Edison... :shock:

For the humor impaired - don't do this. It's not safe.

-Todd

 

[Esoteric]

We have used ethernet equipment to take an Art-net signal and distribute it through a building and used Art-net nodes on the other end. But that is entirely different than what the OP is trying to do.

 

[JohnD]

I'm surprised nobody has asked if they can use a power strip as a DMX splitter.

All you have to do is adapt the DMX 3-pin to Edison... :shock:

For the humor impaired - don't do this. It's not safe.

-Todd

Say Todd, I'm not sure, but I think this company makes the product of which you speak(laughingly).

 

[cpf]

Say Todd, I'm not sure, but I think this company makes the product of which you speak(laughingly).
View attachment 7319

The "Yeah, I'm sure your knockoff Chinese fixtures will work fine" 5-3 adaptor?