Control/Dimming Sending DMX down a single wire (not a single cable)

[jamesterjlrb]

Hi, i'm trying to convrt DMX into a form where it can be sent down a single strand of wire and the converted back into normal 5 pin format at the other end. i'm only really worried about 3 pins. The spare two pins don't matter. Any thoughts? I was thinking serial as you can send that down a single wire. I'd like to make it myself so any freeware instructions/programs would be good.

 

[Chris15]

What's the application?

You can't send any signal down a single wire as you can't form a circuit with a single wire...

 

[Footer]

Serial ports that work that way because they can still use a common ground to close the circuit. The only way to do this would be to convert the signal over to fiber and back to copper. Thats not exactly a single wire, but its a single path. Physics requires 2 paths to create a circuit.

Dare I ask why you want to run it down only one conductor?

 

[STEVETERRY]

Serial ports that work that way because they can still use a common ground to close the circuit. The only way to do this would be to convert the signal over to fiber and back to copper. Thats not exactly a single wire, but its a single path. Physics requires 2 paths to create a circuit.

Dare I ask why you want to run it down only one conductor?

I have to say that I too am quite interested in the answer to that question.

ST

 

[Footer]

I have to say that I too am quite interested in the answer to that question.

ST

You just want to be the one that throws 300 years electrical theory down the tubes!

 

[MNicolai]

Sounds like ST might have another juicy Protocol article about electricity on the way.

 

[Studio]

You tie a dmx cable to the end of the wire go to the other end and pull!

 

[shiben]

what would be the practical use of this? Its not like pulling a DMX cable is much more difficult than pulling any other cable thru a properly sized conduit, and its much easier to pull a DMX cable than pull a single wire from one thru without breaking said wire. I just see no real practical use for this kind of system.

 

[zuixro]

Technically DMX is serial communication. One bit at a time...

Asynchronous too, just like your computer serial port, just a lot faster. (like 250k baud)

If you're looking for reliability, this isn't a good solution. The reason that DMX uses two wires is to cut down on interference (in a way that others here can explain much better than I can)

 

[gcpsoundlight]

Will do zuixro...

The reason that DMX has such good interference rejection is because it is electrically balanced. Your first pin is ground, all your signals are referenced to this. Your 2nd pin is a signal line BUT it is out of phase IE negative in relation to zero at the peak of a wave form (for simplicitys sake at the moment, I will use a sine wave example). The 3rd pin contains the unaltered signal.

Now the cable itself contains 2 (or sometimes 4) wires or conductors. these will be twisted together in pairs, and the outside will have a shield that is connected to pin 1.

Now, the reason it cuts down in interferience is this. When the signal is in the wire, you have on in phase signal, and one out of phase signal. BUT, any pickup interferance will be IDENTICAL to both signals. when you get to the reciever, it will subtract one from the other, whereby the interferance will be removed, but the original signal will remain.

There! If you didn't understand that, look up balanced signals or balanced audio on wikipedia.

 

[STEVETERRY]

Will do zuixro...

The reason that DMX has such good interference rejection is because it is electrically balanced. Your first pin is ground, all your signals are referenced to this. Your 2nd pin is a signal line BUT it is out of phase IE negative in relation to zero at the peak of a wave form (for simplicitys sake at the moment, I will use a sine wave example). The 3rd pin contains the unaltered signal.

Now the cable itself contains 2 (or sometimes 4) wires or conductors. these will be twisted together in pairs, and the outside will have a shield that is connected to pin 1.

Now, the reason it cuts down in interferience is this. When the signal is in the wire, you have on in phase signal, and one out of phase signal. BUT, any pickup interferance will be IDENTICAL to both signals. when you get to the reciever, it will subtract one from the other, whereby the interferance will be removed, but the original signal will remain.

There! If you didn't understand that, look up balanced signals or balanced audio on wikipedia.

All this is nice--but let's get to the meat of the issue--why does the OP want to use a single wire? I have theories, but I'm waiting for his reply.

ST

 

[zuixro]

Will do zuixro...

The reason that DMX has such good interference rejection is because it is electrically balanced. Your first pin is ground, all your signals are referenced to this. Your 2nd pin is a signal line BUT it is out of phase IE negative in relation to zero at the peak of a wave form (for simplicitys sake at the moment, I will use a sine wave example). The 3rd pin contains the unaltered signal.

Now the cable itself contains 2 (or sometimes 4) wires or conductors. these will be twisted together in pairs, and the outside will have a shield that is connected to pin 1.

Now, the reason it cuts down in interferience is this. When the signal is in the wire, you have on in phase signal, and one out of phase signal. BUT, any pickup interferance will be IDENTICAL to both signals. when you get to the reciever, it will subtract one from the other, whereby the interferance will be removed, but the original signal will remain.

There! If you didn't understand that, look up balanced signals or balanced audio on wikipedia.

Thank you for that. I knew how it worked, I just couldn't explain it.

 

[MarshallPope]

Well, the telegraph used a single wire. Therefore, it is possible to transmit using only one, but I am sketchy on how exactly it worked and if somehow the concept could be transcribed to electronic data transmission.

 

[gcpsoundlight]

Yes, the telegraph used just one wire, but really, for this purpose, it would be like having a shower without a plug hole, the water would go nowhere.

Technically, you need 2 wires (actually 3) for DMX, because all voltages or signals are with reference to ground. In theory you could use the electrical ground on the dimmers and fixtures, but you would have so many problems, not to mention danger, and electrical saftey codes.

So, please just tell us why you wan't only one wire? do you intend to use the nails in the roof as tie ins, with the roofing metal as the main carrier!

 

[Footer]

Well, the telegraph used a single wire. Therefore, it is possible to transmit using only one, but I am sketchy on how exactly it worked and if somehow the concept could be transcribed to electronic data transmission.

Giant rod stuck into the ground. The earth was one and the copper was the other. It worked, however all the telegraph did was send voltage across the line. What DMX does is far more complex compared to what the telegraph required.

 

[avkid]

BTW, the last remaining Marconi tower is not far from my hometown.
The Binghamton Marconi Tower

 

[SHARYNF]

If this is just an electroics exercise then it would be possible though not very practicel. you would have to send a series of voltage pulses down the wire and have it be connected to the electrical ground at the other end. You could have the voltage vary to the Byte value (sort of like an old analog dimmer where the voltage was from 0-10 )

This is not exactly what you want BUT give you some idea of how it MIGHT be possible, again using an alternate ground to complete the system


A Tutorial on Convolutional Coding with Viterbi Decoding

So you would have to have a set up that on the transmit side decode the bytes to a voltage pulse, then on the receive side convert these analog voltages back to digital




not practical but in theory data could be transmitted this way
Sharyn

 

[Footer]

If this is just an electroics exercise then it would be possible though not very practicel. you would have to send a series of voltage pulses down the wire and have it be connected to the electrical ground at the other end. You could have the voltage vary to the Byte value (sort of like an old analog dimmer where the voltage was from 0-10 )

This is not exactly what you want BUT give you some idea of how it MIGHT be possible, again using an alternate ground to complete the system


A Tutorial on Convolutional Coding with Viterbi Decoding

So you would have to have a set up that on the transmit side decode the bytes to a voltage pulse, then on the receive side convert these analog voltages back to digital




not practical but in theory data could be transmitted this way
Sharyn

This is the one place where a wireless system would be more reliable then a single piece of copper and probably cost less. Now, you get that new fangled two pieces of copper that those city folk have and you might just have something....

 

[epimetheus]

BTW, the last remaining Marconi tower is not far from my hometown.
The Binghamton Marconi Tower

Marconi was a hack, Tesla was the man!

/threadjack

 

[STEVETERRY]

Giant rod stuck into the ground. The earth was one and the copper was the other. It worked, however all the telegraph did was send voltage across the line. What DMX does is far more complex compared to what the telegraph required.

After we hear the one-wire reason from the OP, we can delve into the intricacies of the common-mode voltage limits of EIA-485 transceivers---and all will be revealed.

ST