Daisy Chain PTZs with Cat 5 cable

[ljk-wxm]

Hi All. We have 2 Sony EVI-D70s. Can we daisy chain them through their RS422 connectors using cat 5 cable?

PC connection would be Serial port > db9 rj45 adapter.

Can anyone help with the wiring diagram for that scenario please?

Many thanks,

Lisa

[daver2]

Hi,

I am a bit confused by your post.

The Sony EVI-D70 has provision for either an RS232 connector (horrid 8-pin round thing) or the VISCA 9-pin linear plug and socket arrangement. You specifically mention the RS422 port in your post - but then describe the RS232 port on your PC. Are you planning on using an RS232 to RS422 converter box at the PC end?

If not - you can't connect the PCs RS232 port up to an RS422 link - at best it wont work - at worst it will go bang.

The VISCA RS422 connector has a TX and RX in pair and a TX and RX out pair. You would join the PC DB9 to an RS232/RS422 converter and then link that to the first camera and then link the first camera to the second camera and so forth. If you can identify the particular make and model of RS232/RS422 converter you are using then I may be able to give you more detailed connection information.

There is no reason why you couldn't use cat 5 cable (we use it in our set-up with those exact same cameras and it works fine).

Dave

[daver2]

Just found this website which may help?

http://blog.ianbeyer.com/2010/12/20/...s-422-control/

Dave

[ljk-wxm]

Hi Dave,

Thanks. You're confused! I'm more confused!

I've seen ian's blog and very good it is too. That's what gave me the idea as I hate the mini din 8-pins also and am trying to steer away from them.

Ian uses that junction box and then a joystick controller RM BR300. I want to use the PC as the controller and avoid buying a custom controller...

So what options do I have to connect to PC? DB9, DB25, USB? This is where I'm not sure what to do...

Lisa

[ljk-wxm]

http://www.google.co.uk/products/cat...d=0CNABEPMCMAI

I found it all by myself. Now - will it make the computer go bang or will computer be happy?

[daver2]

Bang!

The item you have provided a link to assumes that the DB9 connector is already an RS422 Standard serial port and all it appears to be is a set of wires joining the DB9 to the terminal block. If your PC has an RS232 serial port then this will not work.

The RS Standards effectively identify the voltage levels etc. that the serial port will be operating at and whether it is a differential signal (has a +Ve and -Ve pair for the transmit and receive function) or not (a single transmit and receive line).

For example an RS422 line has a pair of receive lines (RX+ and RX-) whereas the PC RS232 port has a single transmit line. Where would you connect the single transmit line to a pair of receive lines on the camera? The voltage levels are also incompatible. An RS422 line will usually operate at +/- 6Volts whereas an RS232 line can operate at up to +/- 15Volts (or greater). In-built PC ports are usually not 'true' RS232 ports and their voltage outputs are generally much lower than the "true" specification says - hence the reason that I would not push a PC connected 232 line to the limits specified by the Standards.

First of all - check out your PC itself. Does it have a true RS422 serial port (in which case you don't need anything - you just need to know how to connect the wires) or does it have an RS232 port (in which case you need an RS232 to RS422 converter unit). Ignore the physical connector - as this has no bearing on matters at this juncture.

I notice that startech.com sell a true 232 to 422 converter (http://intrl.startech.com/Cards-Adap...nverter~IC485S) - although this is fitted with a 25-way connector. If your PC has a DB9 RS232 port then you will require an appropriate DB9 to DB25 converter. This seems an ugly solution!

You can also buy USB to RS422 adaptors and PC cards that are true RS422 serial interfaces. It just depends what ports your PC has, how permanent the install is going to be and what you can find on the market.

For example, a quick Google search identified this product as a USB to RS422 converter: http://www.brainboxes.com/files/cata...-datasheet.pdf

I personally don't like USB devices so we control our cameras (and projectors) via a dedicated multi-port RS422 PC card. This is an example of a PCI single-port RS422 PC card http://www.brainboxes.com/files/cata...-datasheet.pdf.

These aren't the cheapest solutions - and with a bit of googling I am sure you can find a more cost effective solution.

Hope this is of some help - or have I confused you more? If I have confused you even more - try this site: "http://www.takelog.com/Technical/rs232422.htm".

You may also find this document explains things a bit better than I can: http://www.sena.com/download/tutoria...ial_v1r0c0.pdf

Dave

[ljk-wxm]

OK....I looked at the tutorials - ummm.....

Your explanation makes sense though!

So now I know that the laptop's COM port isn't necessarily true RS232 and I'll need a PCMCIA 422 single port to do without the Sony controller.

OK. I understand that. Thank you too for the links.

I looked at what we currently have (i.e. just the one camera controlled by the laptop via RS232 I think....) and have attached photos of the adapter (same thing from 2 angles) that goes into an ordinary laptop port.

What on earth is going on there? Can you interpret it?

Lisa

[daver2]

Lisa,

Assuming your photo is the RS232 DB9 end that plugs into the laptop - it will have a single Transmit wire, a single Receive wire and a ground wire as a minimum.

The other lines will be what are known as "hardware handshake" controls and are designed to ensure that data bytes (or characters) within the message don't get lost. For example, in a work environment, if your boss tries to give you too much work to do you will say "just a minute while I finish the last lot off before I start something new". This is the purpose of the hardware handshake lines.

When the PC wants to send a character to the projector/camera - it should operate the Request To Send (RTS) line which is transmitted down the cable to the projector. The projector/camera will see that the PC wants to send a character and - if it has space to store the character - will tell the PC (via the Clear To Send - CTS) line that the PC can send the character. The PC will then transmit the character. Likewise, if the projector/camera wants to send a character - the PC will have to tell the projector/camera that it has space to store the character and that it can go ahead and send it.

Now the rub - not all equipment obey this hardware handshaking protocol - so it is possible to software disable it at the PC end - or you can "loop back" the hardware handshake lines so that they are ineffective. Successful transmission between the equipment then relies on using low speed communications (a low baud rate) or luck/prayer!

Some designs of remote equipment also do not need hardware handshake lines (in the receive direction at least) if they can guarantee to process all of the data sent to them at the fastest baud rate they are designed for. This usually means they have a built-in data buffer and the communication protocol between the PC and the remote equipment expects a "message handshake" back from the remote equipment in response to a command that is sent. For example (on a projector) the PC may ask for the screen to be blanked - the projector would respond with an OK when the command has been completed and the PC will expect this before sending the next command. This exchange of messages ensures that one piece of equipment is not overrun with messages too fast.

When building up a cable - you would generally wire the hardware handshake lines up - hence the multitude of cables in your plug.

Looking at the technical manual for the EVI-D70 (http://www.norbain.co.uk/downloads/m...vi-d70(op).pdf) in VISCA communications mode it specifically states (on page 31) that "flow control using XON/XOFF and RTS/CTS etc. is not supported". The interconnecting diagram (on page 35) between the camera and a Windows DB9 shows some of the hardware handshake lines wired up (even though they aren't used...) and some looped-back (RTS/CTS) on the PC DB9. This has probably been done to ensure that the PC end works rather than anything to do with the camera end.

It would appear as though the Sony EVI-D70 does not require hardware handshake control and, therefore, only transmit, receive and ground are required to be connected up (assuming the software in the PC doesn't expect to be using hardware handshaking - in which case the lines need to be connected up to 'fake' the fact that the PC is connected to a piece of equipment which is always "ready").

The 9 pin VISCA RS422 connector on the camera only has the transmit and receive pairs anyhow - no hardware handshaking.

How are we doing. Are the mists clearing?

Dave

[ljk-wxm]

The mists are clearing, yes. Thank you so much for all that explanation. Now I see that some software needs to 'think' there's handshaking going on and that one can fool it with loopback.

You have explained it in plain English - all the other stuff I've read on the web has been a bit too difficult for a beginner like me.

So, Dave, if you haven't totally scraped the barrel of patience, one last thing... why is it not possible to get a PCMCIA RS232 Port with an RJ45 socket so that one can use the nice familiar Cat5 or 6 and not have to wire terminal blocks or solder DB9s? See - I'm still a bit puzzled!

Lisa

[daver2]

Lisa,

The quick answer is that the RS232 Standard has been around for longer then PC's have. It was around in the days of mainframe computers when dumb terminals were connected to the mainframe via modems. The Standard at that time was a large 25 pin connector (a DB25). Because the speed of these links were so sloooow - the handshake lines were necessary. Plus there were extra lines for other modem control signals.

The early PC's (IBM PC and XT) used the 25 way RS232 connector because (at the time) it was the standard. As things moved on - and PCs became smaller - there was a requirement for a smaller RS232 connector - and the DB9 was born. Most of the non-essential handshake signals were stripped out to just leave the bare essentials to drive peripheral equipment and the like.

Things move very quickly in the PC world - as opposed to the world of Standards where things move very slowly. Most of the RS232 ports started to die out in PCs with the advent of USB and later derivatives.

So the answer probably is that there has been no real market for the major PC manufacturers in recent years to develop such things. If you hunt around you will find PC RS232 cards with RJ45 connectors fitted as standard. Although I agree with you - I have never seen a PCMCIA card fitted with one. I personally don't like the RJ45 connectors due to their flimsiness. One of the advantages of the DB9 or DB25 is that it is a very damage-resistant connector in an industrial world - which is still where most of the RS232, RS2422 and RS485 equipment is used.

Don't worry - even seasoned professionals get confused by communications links! If communicating between two pieces of equipment was easy I would be out of a job

Dave

[ljk-wxm]

Thanks Dave,

Again, a great explanation. You've been a real help.

Lisa

[daver2]

My pleasure.

Dave