T tapping the data line

[tpctech]

A USB adapter is another "node" on the RS-485 network...line...wire. It really should not matter where it is.

I have a commercial display the is run off a director. The director only has 1 RJ45 jack. I have a RJ45 "tee" connected right into the director then a cat runing north and south a 3 city blocks in both directions. There are 10 LOR boxes on the network. It is still a straight in-line network with no "Stubs" or "tee" and all in a line just witht he director in the middle.....

I have worked with RS-485 in the industrial control DMX lighting world for 25 years!



KEN

[Guest guest]

terrypowerz wrote:

Ok, I am confused....

Orville, (Clay, Wilbur...whatever) cracked open his USB adaptor.... NOT a repeater.

It is a totally different animal.... it is at one end of the network, not midstream like the repeater is intended for...

I don't think that anything useful has been learned here.

I NEVER said I cracked open a "repeater" anywhere in this thread. I said I cracked open my USB485B unit.

I made reference to the repeater because I thought it had a power LED on it, but it was a different USB485 unit I was thinking of, and NOT a repeater from a reply about adding a power LED to my USB485B.

[Guest guest]

tpctech wrote:

A USB adapter is another "node" on the RS-485 network...line...wire. It really should not matter where it is.

I have a commercial display the is run off a director. The director only has 1 RJ45 jack. I have a RJ45 "tee" connected right into the director then a cat runing north and south a 3 city blocks in both directions. There are 10 LOR boxes on the network. It is still a straight in-line network with no "Stubs" or "tee" and all in a line just witht he director in the middle.....

I have worked with RS-485 in the industrial control DMX lighting world for 25 years!



KEN

Are you using this director unit Ken? (DC-MP3 Showtime Director)

http://store.lightorama.com/inmp3di.html

This is the one I use and it has 2 RJ45 jacks on it, if yours does not and it is the same unit, it must be an older generation unit. As I thought all the MP3 Director units had 2 RJ45 jacks on them.

I bought mine in the January/February 2010 time frame.

[tpctech]

Orville wrote:

tpctech wrote:

A USB adapter is another "node" on the RS-485 network...line...wire. It really should not matter where it is.

I have a commercial display the is run off a director. The director only has 1 RJ45 jack. I have a RJ45 "tee" connected right into the director then a cat runing north and south a 3 city blocks in both directions. There are 10 LOR boxes on the network. It is still a straight in-line network with no "Stubs" or "tee" and all in a line just witht he director in the middle.....

I have worked with RS-485 in the industrial control DMX lighting world for 25 years!



KEN

Are you using this director unit Ken? (DC-MP3 Showtime Director)

http://store.lightorama.com/inmp3di.html

This is the one I use and it has 2 RJ45 jacks on it, if yours does not and it is the same unit, it must be an older generation unit. As I thought all the MP3 Director units had 2 RJ45 jacks on them.

I bought mine in the January/February 2010 time frame.

OPPS. Yes the director has 2 jacks when I was debugging the program with the computer connected I used a "Tee" on the output of the dongle. I know I used a "Tee" .....sorry for the confusion. Basically as long as all device are along the wire with no "stubs" all should be fine.

KEN

[terrypowerz]

Orville wrote:

Max-Paul wrote:

Couple of my thoughts about Orville's questions.

The repeater with dual outputs. Each of those outputs are treated as two individual circuits that merge going back to the computer. Meaning each of those outputs more than likely have their own RS-485 chips with the inputs tied together in parallel.

Ok, why you want to avoid stubs (T) circuits. As Steven pointed out. In a normal RS-485 daisy chained topology you have two points that can cause reflections. With stubs each stub becomes a reflection point. In the normal circuit you put termination resistors of 120 ohms at each end to kill any reflected signal. But if you did this at the end of each stub. Then you would load down the circuit to the point you would now kill the wanted signal.

Just cracked open my USB485B with power booster, nope, only has one 485 chip in there. Both cat5 sockets wired together in parallel to the single 485 chip.

Just so you know.

Clay,

Correct me if I am mistaken, but since you replied to the above quote and colored the quoted text RED I assumed you were cracking it open in response to the mention of the Repeater... which IS intended to provide operation of a stub geometry.

The single chip in a USB adapter works just the same as a controller...being able to be in the "middle" of a network.... the only difference being the adapter acting as the source of the majority of the communication.

I thought discussion was as to the ability to "Y" off one of those 2 branches downstream and what may be inside the Repeater unit that allows this configuration.
(which it does)

I was able to read what you claimed you did, just didn't know how it pertained to the RED highlighted quote that you did above...

[Guest guest]

terrypowerz wrote:

Orville wrote:

Max-Paul wrote:

Couple of my thoughts about Orville's questions.

The repeater with dual outputs. Each of those outputs are treated as two individual circuits that merge going back to the computer. Meaning each of those outputs more than likely have their own RS-485 chips with the inputs tied together in parallel.

Ok, why you want to avoid stubs (T) circuits. As Steven pointed out. In a normal RS-485 daisy chained topology you have two points that can cause reflections. With stubs each stub becomes a reflection point. In the normal circuit you put termination resistors of 120 ohms at each end to kill any reflected signal. But if you did this at the end of each stub. Then you would load down the circuit to the point you would now kill the wanted signal.

Just cracked open my USB485B with power booster, nope, only has one 485 chip in there. Both cat5 sockets wired together in parallel to the single 485 chip.

Just so you know.

Clay,

Correct me if I am mistaken, but since you replied to the above quote and colored the quoted text RED I assumed you were cracking it open in response to the mention of the Repeater... which IS intended to provide operation of a stub geometry.

The single chip in a USB adapter works just the same as a controller...being able to be in the "middle" of a network.... the only difference being the adapter acting as the source of the majority of the communication.

I thought discussion was as to the ability to "Y" off one of those 2 branches downstream and what may be inside the Repeater unit that allows this configuration.
(which it does)

I was able to read what you claimed you did, just didn't know how it pertained to the RED highlighted quote that you did above...

The reason that was quoted is because the USB485B also has two RJ45 jacks and seeing that they said the repeater was 2 different indepent RS485 circuits, it would figure that any of the RS485 units with dual RJ45 jacks would be wired internally the same, 2 data circuits, which the repeater seems to have, the USB485B does not.

That's what I was trying to discertain and find out, so when I opened the USB485B, that is what I found out and just posted that info. I don't have a repeater, so I can't actually open one and look into it, so I have no idea if it truly has two data circuits or not, just know what I have does not.

The repeater came into the conversation a bit later and I was thinking it had a power LED, don't recall if it was the repeater or another 485 item that has the power LED, but was thinking of adding one to my USB485B so I'd know power was actually getting to it from the USB port from the computer, and that's how this whole mess got instigated. Along with a few other questions about the T adapters.

[garyfunk]

The simple answer is: You can tap an audio signal, though you will get some loss. You cannot tap a digital signal. It will throw off the timing and induce noise.

[Steven]

Orville wrote:

... the USB485B also has two RJ45 jacks and seeing that they said the repeater was 2 different indepent RS485 circuits, it would figure that any of the RS485 units with dual RJ45 jacks would be wired internally the same, 2 data circuits, which the repeater seems to have, the USB485B does not.

The repeater has 3 RJ45 jacks, one on the front, and two on the back. The 2 on the back are connected in parallel.

don't recall if it was the repeater or another 485 item that has the power LED,

The USB-485-ISO (USB Isolated Adapter) has a power LED. I don't remember if the repeater has one; all you can see from the picture is the "Status" LED, which probably performs the same function.