# Controlling multiple RS-232 devices



## DiscoBoxer (Dec 18, 2013)

I have limited experience with RS-232 control.

I am looking to control ten Kramer VP-443 video switcher/scalers. Want to make it stupid simple and use three mechanical buttons to change the switchers between the 3 potential inputs fed into all ten Kramers.

My plan is to use a Global Cache GC-100-12 to connect mechanical buttons to the three relay contactors. Then output from the Global cache via RS-232 to all the Kramer switchers for simultaneous switching. I cannot find a RS-232 hub/switch/distributor to take the 1 output of the GC and broadcast to 10 inputs of the switchers. Know of any?

If my understanding is correct, I only need to send data to switchers but not receive. What would happen if I convert serial to RJ-45 and use a standard data hub?

Assistance would be appreciated.


----------



## Lextech (Dec 18, 2013)

The easiest way I know, admittedly very expensive, is Alcorn McBrideis V16. It has contact closures to 16 RS 232 ports. Overkill for you job but it is bullet proof. BTW what are you trying to accomplish? Are all the ten switchers doing something different content wise?


----------



## DiscoBoxer (Dec 18, 2013)

Correct. Essentially, I have 10 screens & 3 video servers that output 10 independent feeds each. I want to switch the content by essentially switching between the three video servers. Instead of using a matrix video switcher, the economy route was to install switchers for each display. I will peek at the Alcorn you suggested.


----------



## Lextech (Dec 18, 2013)

Well with that much gear you might be able to afford the V16. Here is the link.

http://alcorn.com/products/v16plus/index.html


----------



## DiscoBoxer (Dec 18, 2013)

The v16 is an interesting piece. It does look like a bit overkill, but I requested a quote and will review specs to see how it can fit into the mix. Stable is good and these are rated for 24/7 operation, so that is a plus! Thanks.


----------



## Lextech (Dec 18, 2013)

They come out of the theme park market, think mouse ears. Failure is not an option. I used the V16 for 8 years for show control in a theater never had a problem. Built a commercial insertion system that ran 24/7, or at least the V4 did, turned everything else off at night woke it it in the morning. Triggered a switcher, plasma display and a hard disk recorder. Ran for 4 years before i left in 2006. They might be using it still as far as I know.


----------



## Drew Schmidt (Dec 19, 2013)

In answer to your other question, because someone might try it some day, yes, you could wire the RS-232 cable to RJ-45. Copper to Copper. You might mess with the cable's shielding etc, but I've certainly done this with wonderful results. We were then able to use the existing RJ0-45 artery system in a building. But *no* you cannot use an RJ-45 hub. You're dealing with a specific type of digital signal (i.e. TCP/IP) whereas the RS-232 is a simple analog signal. Sorry.

With that in mind, I would guess that if you tried to simply split the RS-232 cable into multiple runs, the signal voltage would drop (much like using an unpowered XLR splitter). 

(Here's a splitter)
http://www.monoprice.com/Product?se...&cagpspn=pla&gclid=COey4vauvLsCFYg-MgodYiQA_Q

Not sure how many times you could get away with this.


----------



## Chris15 (Dec 19, 2013)

My gut is to say that if all the switchers are in the same rack, connected to the same power, then you probably could get away with splitting the RS232 signal, just wiring pin 2 or 3 (I can't remember which is TX and which RX without checking a pinout) and pin 5 in parallel.

I don't like that cable @Drew Schmidt posted, it looks uncomfortably like it might be wired in a way that means that 2 TXs are connected together and that will not be good for the long term health of the tranceviers, and may not be good for their short term health either...

You might run into loading issues though, and it might be best to try and find a device with a handful of 232 outputs and only daisy them to 2 or 3 each...


----------



## museav (Dec 19, 2013)

DiscoBoxer said:


> I am looking to control ten Kramer VP-443 video switcher/scalers. Want to make it stupid simple and use three mechanical buttons to change the switchers between the 3 potential inputs fed into all ten Kramers.




DiscoBoxer said:


> Correct. Essentially, I have 10 screens & 3 video servers that output 10 independent feeds each. I want to switch the content by essentially switching between the three video servers. Instead of using a matrix video switcher, the economy route was to install switchers for each display. I will peek at the Alcorn you suggested.


Two questions. What type of video signals are involved? And do you need scaling for all display devices or since you have a dedicated output per display, could the media servers be setup to match the resolution and refresh rate for the associated displays or simply use 'passed through' EDID?

You'd apparently need a 30x10 matrix router, but I would think that would be a lot easier than having to deal with 10 separate switchers. While the equiment may be a bit more costly upfront, a Crestron DigitalMedia or AMX Enova solution may be a good option to provide the routing and scaling as well as CAT/STP distribution to the displays if desired.


DiscoBoxer said:


> If my understanding is correct, I only need to send data to switchers but not receive.


That depends, do you care to know if they actually switched or are you just going to send the command and assume they all react as desired? If you do not require return communication then you may not want to wire for it or you could run into issues with a serial port receiving multiple responses at the same time.

I have to agee that while you could have multiple identical devices receiving commands from one serial port, you might want to avoid trying to tie 10 devices to a single port.


----------



## DiscoBoxer (Dec 19, 2013)

The video servers are outputting via HDMI at 720p. I decided to use scalers due to text heavy content and wanted to output 1080p...and keep the TVs happy. The video cards will always see a live device (the scalers) and not cause funky issues with display detection in the array.

I'm limited on my understanding of RS-232 communications, therefor I do not understand the significance of receiving a "return" communication from the switcher. In a duplex RS-232 communication, would the host continue to send command if one of the switchers does not switch?


----------



## museav (Dec 20, 2013)

DiscoBoxer said:


> The video servers are outputting via HDMI at 720p. I decided to use scalers due to text heavy content and wanted to output 1080p...and keep the TVs happy. The video cards will always see a live device (the scalers) and not cause funky issues with display detection in the array.


I have no problem with using a switcher/scaler for each display but mentioned it since the budget seemed a factor in terms of the serial communication and not using a matrix router.

Your content is 720p so that is what you have for information and any greater resolution is going to contain interpolated data. I will bet your displays accept 720p signals and thus mapping the 720p source signals to the 1920x1080 native resolution of the displays is essentially the same whether you use a dedicated external scaler or the integrated scaling of the displays (pretty much all digital displays incorporate internal scalers). A dedicated scaler will typically provide a better result than the internal scaling of the display but at a cost when providing a dedicated scaler for each display.

Whether the video card is seeing the input of a switcher/scaler or the input of a switcher or matrix router without scaling is not necessarily any different, it's all up to how the devices can handle EDID and how you have them programmed to handle it. Something like the Kramer VS-3232DN loaded with appropriate HDMI input and output cards appears to provide the capacity and EDID management desired and when combined with the internal scaling of the displays seems to provide the same general functionality but with one device instead of ten. I have no idea if that might be a more cost effective option or not.



DiscoBoxer said:


> I'm limited on my understanding of RS-232 communications, therefor I do not understand the significance of receiving a "return" communication from the switcher. In a duplex RS-232 communication, would the host continue to send command if one of the switchers does not switch?


Typically, if you send something like a "switch to Input 1" command the device would make the switch and then reply with a string to indicate it had completed the switch (or possibly an error string if something went wrong). That provides positive feedback that the switch occurred. In your application that could have two implications. Without that return communication you can only assume the switch(es) actually took place as you do not receive the confirmation from the devices themselves. That may never be an issue unless a switch does not happen when someone thinks it did, then it may become an issue. On the other hand, if you do have return communications and a port on your controller is shared by multiple devices then you may receive multiple strings at once, causing communication errors.


----------



## FMEng (Dec 20, 2013)

One RS-232 output can drive several inputs by making your own cable. It would connect the source transmit data to receiver data on each switcher, along with ground. TD on each switcher would be left un-connected. There is a limit to how many inputs an RS-232 output can drive. My guess is four inputs together would be about the limit for reliable operation. I have built an RS-232 distribution amplifier, using the Max-232 chip. Just avoid the Texas Instruments version of the chip and take ESD precautions.


----------



## vman (Dec 20, 2013)

I think V-Control could be a good solution for you. A setup for your needs can be:


an industrial, 24/7 capable PC with Windows or Linux operating system (approx. 600 $)
10 RS232 serial ports as PCI board or USB -> RS232 converter (approx. 300 $)
a controller to interface the three buttons with the PC such as V-IO (approx. 220 $ or less if you build your own)
V-Control Software (free GPL)
I don't know how much an Alcorn McBride V16 cost, but this solution will cost around 1000 $.

You can save 300 $ if you skip the ten RS232 ports and use a RS232 splitter cable as mentioned above. I have successfully used this in the past, but only for three devices. Maybe you can buy 4 RS232 ports (approx. 120 $) and then split the Tx to max. 2-3 Kramer switcher.
If you use the 10 RS232 ports you have the advantage that you can receive the Acknowledge from the switchers.
Of course you can use a cheaper PC as well. Any system with ATOM CPU is capable to run V-Control.
If you want a much cheaper controller to interface the three buttons you can use a simple Arduino Board (approx 30 $)

If you are interested in this solution I can help you writing the device driver for the Kramer switcher, writing a sketch for the Arduino and writing a small V-Control project.


----------

