RS232 down digi grade cable?

Stuart Hogg

Hi there,

First time on this forum, very glad to have found it.

I've got a few Soundweb 9088s on the go. I've got one which will be living in an amp rack on stage, and I'd really like to extend the RS232 control to FOH. It so happens that I have a spare line on an AES/EBU multi. (Van Damme \"Green\" series)

I'm told that it *should* be possible to run RS232 down it. In theory all I'd need to do is make up adaptors from DB9 to XLR? If that's the case, can anyone tell me the pinning? Or is there more to it than that?

Thanks,

Stuart

JoshM

Hi Stuart!

I have heard rumors of people using up to a total length of 90 meters of snake and microphone cable and experiencing adequate operation of RS-232 serial communications with the dbx DriveRack series products.

I would assume that AES/EBU cable would be a great cable to use for this application.

I have done RS-232 down a 30 meter section of snake trunk with no difficulty. I have also done full duplex RS-485 communication using 2 snake lines in a 54 pair Ramtech Ramlatch snake system. I wanted to use the dbx DriveRack 480R out at FOH and leave the 481's in the amp racks by the stage. This system works incredibly well!

I would HIGHLY recommend if you are going a distance longer than 30 meters to get some 232 to 422 converters. Fortunately serial communications can be done over some surprisingly long distances. The big issue at hand is that the RS-232 standard is an unbalanced interface, whereas the 422 and 485 standards are balanced. So, using all the knowledge we all have of why balanced interfaces are better than unbalanced, it becomes clear that to convert from 232 to 422 for a long run makes good sense, then converting back from 422 to 232 at the far end you will be able to do a long distance 232 interface that will be quite immune to all the nasties that are present with the typical unbalanced situation.

In order to facilitate full duplex 485 and 422, you will most likely need to use TWO snake channels. Be certain to use one snake channel as the TX pair and the other snake channel as the RX pair. Do NOT just take snake channels and connect them to conductors. You NEED to make CERTAIN that you have both the TX conductors on the same snake channel and both the RX conductors on the same snake channel... this goes back to the basics of the balanced interface.

Typically the RS-232 interface uses pins 2 and 3 for the data TX and RX and pin 5 is the ground. Which pin, 2 or 3, is the TX and which is the RX will depend on your device. You need to check with the manufacturer to see which is which.

Yes, you can typically just make a DB-9 to XLR adaptor to run the serial information down the snake. Just take some time to insure that you are connecting the wires correctly on each end. In my situation above where I wanted to remote the DriveRack 480R from the 481's, I put the rack mount power supply for the 480R out front with the 480R and just used a DB-9 to two XLRs to connect it to the snake system. This way the power supply would ALWAYS be connected to 480R so there would be no issue with blowing them up when connecting them while the power supply is turned on. Then, at the amp rack, I used another DB-9 to two XLRs to connect the snake to the serial connection. Like I said before, the system works flawlessly... until one of the meat-heads that uses the system reverses the XLR connections... then it doesn't work at all. hahahah!!!! This only encourages them to keep their mitts off.

Please let me know if there is anything here that is not clear.

Have fun out there!

-Josh

dougmelbourne

The first time I saw someone sending RS232 down a mic lead it was running to an EV DX38 processor down 200 meters of House Multicore system. When I sergested to the House tech that it couldn't be good to send data that far in an unbalanced form and that I thought it couldn’t be within the spec his simple response was \"Yeah? But it works.\"

Since then I've started modifying serial cables with 3 pin XLR’s. there are three adapters I make.
DE9-F to XLR3-M for my laptop.
A null modem XLR3-F to DE9-F
And also a straight through serial XLR3-F to DE9-M.

The straight through Male to Female Cables are Wired
XLR Serial
Pin 1 – Pin 5 Data GND
Pin 2 – Pin 2 Data Receive
Pin 3 – Pin 3 Data Send

The Female to Female Null Modem Cable is the same except they cross over send and receive
XLR Serial
Pin 1 – Pin 5 Data GND
Pin 2 – Pin 3 Data Send
Pin 3 – Pin 2 Data Receive

So! You’ve made your adapters and there isn’t any love coming when you patch it all together. If you have another serial cable test if with that. If you’re new cable is the problem there’s some more soldering to do.

A DE9 Serial connector pin out is as follows.
Pin 1 - Carrier Detect (CD)
Pin 2 - Receive Data (RD)
Pin 3 - Transmit Data (TD)
Pin 4 - Data Terminal Ready (DTR)
Pin 5 – Signal Ground (SG)
Pin 6 - Data Set Ready (DSR)
Pin 7 - Ready To Send (RTS)
Pin 8 - Clear To Send (CTS)
Pin 9 - Ring Indicator (RI)

In the back of each Female connector make two links
Join Pin 7 to 8 so if the hardware asks says it’s ready to send it gives itself a clear to send response immediately.
Join Pin 4 to 6 and 1 so when the unit says DTR (I’m here) it gives itself the DSR (I’m here too) and CD (I’m on the line) Responses.

With the Male connector Make the same two links but leave pin 1 out of the second link as you would be joining two transmit pins together.

I can’t guarantee what the maximum usable cable length is at the baud rate of a soundweb but make some adapters and give it a go with the cabling you’ve got! If it all goes to the dogs don’t use it for a show! Otherwise Happy Sailing

Good luck!
Doug

Tomorrow We’ll discuss how I converted my Weller Soldering station to 3 pin XLR to achieve more flexibility and better reliability.

Bootsy

This worked like a charm!

I used this to connect the Behringer DCX2496 to my PC through a 28 channel XLR multicable. (Only used 1 channel for this ofcourse) total lenght is about 30 meters. If I mute one of the channels, it takes about 300 ms to reach the crossover.

thanks

victoria

Hello guys,


I have a blueprint for a side chain connector for my tracker. I'm going to use TRS connectors instead of XLR so it can patch into my patchbay. My question is where does the +,-, and ground go. I'm guess the + goes to tip (pin 2 on an XLR), the - goes on the ring (pin 3 on XLR) and the ground goes on the sleve (pin 1 on XLR), is this corect?



Regards
Victoria Heden
usamagicsing.com