Coaxitron to RS485

[jodie 0]

Hi All,

 

I've been through the threads here (and elsewhere) and I've seen a lot of solutions for RS485 -> Coaxitron, but not the opposite direction.

 

Looks like Coaxitron is embedding RS422 up the coax. So I'm thinking this box would need to have a fairly decent amount of smarts for both level and address matching.

 

The upshot is that I need to yank an old Pelco Spectra and replace it with one of our OEM cameras. The controller and matrix are talking up the coax, I have 2-wire 24AC and Coax Video (embedded Coaxitron) at the camera, and pulling wire is an ugly option.

 

The camera talks RS485 Pelco P/D as one would expect.

 

So, does a box exist out there that will take the coaxitron from the switcher/controller and do the level match/address translation and bring two wires out to talk 485 to the camera?

 

Thanks for any input!

 

--- Jodie

[hardwired 0]

Sennetech makes a lot of different code translators, this one seems like what you need- http://www.sennetech.net/Manuals/SCT_CRX/sct-crx-pelco-pelco.pdf

[jodie 0]

Hi There Hardwired, thanks for the reply!

 

I had seen that and dismissed it because it was 422 rather than 485. That said - the levels are the same between 422 and 485, signal is the same, it's really just 4 wire vs 2 wire. The camera may be able to do 422.

 

The other option is probably to call Sennetech on Monday and ask 'em.

 

Thank you for the research!

[jodie 0]

Huh, that spec sheet's a little confusing. I've been interfacing dissimilar devices since the [cough] late seventies, and "Random Standard Number" is pretty familiar. That device has two wires, labeled "Pelco Data Out" and claims to be an RS422. Now here I always thought the difference between 422 and 485 was four wire-vs-two wire, and the fact that 422 has some nasty ground-loop issues that can actually pop the bus drivers, but... Anyway - If I have a +/- 485 input on the camera, and +/- 422 output on the converter, isn't that really half a 422 or a full 485 without the echo of data in/data out collisions?

 

[boggle]

 

I'll write to them and see what they have to say for themselves.

[hardwired 0]

Huh, that spec sheet's a little confusing. I've been interfacing dissimilar devices since the [cough] late seventies, and "Random Standard Number" is pretty familiar. That device has two wires, labeled "Pelco Data Out" and claims to be an RS422. Now here I always thought the difference between 422 and 485 was four wire-vs-two wire, and the fact that 422 has some nasty ground-loop issues that can actually pop the bus drivers, but... Anyway - If I have a +/- 485 input on the camera, and +/- 422 output on the converter, isn't that really half a 422 or a full 485 without the echo of data in/data out collisions?

 

[boggle]

 

I'll write to them and see what they have to say for themselves.

It's usually fine to drive a RS485 camera with a 422 output, the differences aren't usually a problem (cameras just use data in, unless you are using alarm outputs from them), and RS485 is tri-state logic with a normally floating output to allow multiple senders on the same bus, also not usually a problem in that instance.

 

I'd certainly defer to Sennetech, though, they've been doing this for a long time.

[jodie 0]

Thanks!

 

Spoke with Jim, and left with the impression it'll do exactly as we figured, and accomplish the goal.

 

Just to close the loop, I'll follow-up next week with the results.

 

Thanks again for your advice!

 

--- Jodie

[jodie 0]

It "almost worked". It "almost worked" in a way that lead Sennetech, after a support call, to suspect the unit they sent was failing. So they sent another unit as a replacement.

 

We're just waiting to schedule a time to head out there and put the replacement in.

 

To Be Continued...

[jodie 0]

Ok, I can finally put this one to bed.

 

First off - the Sennetech folks are outstanding. It's rare that I would ever call support, and rarer still that I'd be speaking with peers in the EE space, but that's the case here. They know their stuff, and are very very helpful in troubleshooting, spending whatever time is necessary to accomplish the goal.

 

It's been most of a couple weeks now and the client reports the PTZ working solidly - so this does appear to be the correct solution for this job.

 

And a big thanks to "hardwired" for your recommendation!

[hardwired 0]

Great to hear it's working well. My interactions with Sennetech have been similar, that's why I don't hesitate to recommend them.

[survtech 0]

FYI. RS422 and RS485 are the same if you don't need bi-directional communication. PTZ control is typically only one-way (control unit to PTZ). The only time you would need bidirectional RS4xx is if you want to utilize alarms or some other function within the PTZ that needs to send data back to the control unit.