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Some few years ago I ran across a specialized cable for RS485 data communication.
The cable was double shielded, heavy duty jacket, two power conductors and a separate twisted pair for data, not sure if it had one more layer of shield over that.
My Google searching did not get me any promising results so any information any one ca share in this matter will be greatly appreciated.
Please use the description above for the basic requirements for the type of cable I need.
Regards,
Nick
This is probably of no help but have you considered a low baud rate in place of a deluxe cable?Quote:
Originally Posted by NickMu
I use standard (non Cat) telephone wire for example and at 300 baud (typing speed) it seems bulletproof.
Norm
Thank you Norm for your input.
My application requires a minimum 19.200 baud rate (I hope to get 38.400).
High noise environments and harsh humidity combined with sun exposure (ocean + Florida are the key words) are asking for highest quality cable I could get. It will be nice to keep the price as low as possible considering that I will be using quite large quantities but in this particular case the quality comes first.
I forgot to mention also that it has to be stranded wires with a gauge around 22 AWG.
Regards,
Nick
Perhaps wireless would simplify the material setup requirements.Quote:
Originally Posted by NickMu
What distance is required?
Norm
See Belden 3109A or for listing.
Norm
Thank you again Norm.
The total cable length is about 150’.
Wireless is not an option due to the fact that the remote module (slave) will, at some point, be submerged and a 100 % reliable connection is a must.
The cable you suggested fits some of the requirements but I’m looking for only one twisted pair and two power wires. Heavy duty jacket and shielding are a must along with availability in large quantities with no lead time. I will be employing half duplex communication using a custom protocol.
I can not express enough how much I appreciate your help.
I might have to contact some of the major cable manufacturers for some help but I tried the forum first hopping that someone might already be using something like this and knowing that is nothing I can do until after the weekend.
Regards,
Nick
For 150' could the cable be enclosed by a continuous length of black plastic flexible pipe?
Norm
Hi Norm,
I need a bending radius on a few inches. The cable will be protected by mesh sleeving to preserve flexibility and add more toughness to it.
This project of mine is in its infant stage. I’m sorry that I did not take the time to fully explain the requirements but I myself don’t have all the information yet. I’m collecting all the information I can before committing to a final design approach.
The RS485 half-duplex and maximum 4 wires cable (power + twisted pair) is already decided and can not be changed.
I found a good (but not ideal) Belden cable 3106Aas a candidate. Its only problem is that does not give me a separate GND wire.
Dave,
Your suggested cable seems robust enough.
I only have one question: can one of the twisted pair be used for power transfer to the slave unit? I was told that the data wires should be twisted and power wires should be normal.
Thanks for the input.
Nick
I've never seen a requirement that the power pair be non-twisted and doubt that twisted pair would cause a problem.Quote:
Originally Posted by NickMu
I found it merely by searching Bing using 'rs485 cable power shield waterproof' so your questions would best be addressed to the supplier.
Since you only need half-duplex, this should cost a bit less.
http://www.hyperline.com/catalog/cab...sf2-a-pe.shtml
I was targeting the same one after you gave me the link.
I will contact the manufacturer for more information and get back with my findings.
Thank you again Norm and Dave for your prompt responses.
Nick
I have been sending power along with RS485 for several years on CAT5 (twisted) with no problem at a baud rate of 300 although that may make no difference.
Norm
Any particular reason why you limited your highest baud rate to 300?
Does it have to do with the power transfer, distance or just you did not need higher baud?
What kind of current can you safely deliver to the slave? I need 50 – 100 mA.
I can only guess that you used a diode on each data line and still power from them. If so what is the ratio between signal / no signal timing in your system?
I need a 20 ms frame within which 10 to 12 bytes will be exchanged between the master and slave with a minimum 5 ms free, on each side, for other tasks. This forces me to use 19200 or higher baud rate.
Can you share a concept schematic of your setup?
Thanks again and again.
Nick
The project was to add a PC to log to a nursing home nurse call system to record the room number and the length of each call.Quote:
Originally Posted by NickMu
For that project their was no advantage in using a higher baud rate so keeping it to 300 was a good thing.
The power over CAT5 was only to power one side of an isolated RS485 transceiver which amounted to little ma.
Their was a neg ground difference between the two endpoints which would cause a regular RS485 to eventually fail.
Use of the isolated RS485 solved the problem.
Found this:
Also One wire serial comms on +5V line from the master Melanie.Quote:
From: "atilla" <[email protected]>
To: <[email protected]>
Subject: Re: picbasic-l RS485
Date: Friday, May 28, 2004 10:31 AM
Been wondering that myself. Though for power and data in a singel cable the best, I think, would be DeviceNET cable. Its built just for it. Though a rea PIA wit strip down. 2 pair cable, each pair shielded on theri own and then the whol cable is shielded again.
Norm
I’ve been testing similar approaches to the suggested solution to RS485 or other parasite power systems and my results were not consistent enough especially when dealing with 5V power / data line and high current needed at the slave end. 12V setups are better but still not reliable enough for my power needs for the slave unit.
Regards,
Nick
You might also consider PoE that are cheap devices and use standard RJ-45 sockets.
Ioannis
PoE is a nice choice but unfortunately my slave has space limitations and I must keep it to a minimal component count. My slave board cannot be larger than 1.5 square inches.
I’m hopping to get it done with one small PIC (PIC12F683 maybe) and one 8 pin RS485 chip (still WIP).
Regards,
Nick
Here are the best two cables recommended by the manufacturer just in case someone might be interested:
http://www.hyperline.com/catalog/cab...c5e-p-io.shtml
http://www.hyperline.com/catalog/cab...sf2-a-pe.shtml
First is a four twisted pairs and the other is a two twisted pairs.
Regards,
Nick