View previous topic :: View next topic |
Author |
Message |
ATIU
Joined: 15 Oct 2004 Posts: 534
|
Posted: Wed Feb 21, 2007 2:04 pm Post subject: RS485 wiring requirement |
|
|
This may not be a BASCOM related topic, but I find this forum full of very knowledgeable and helpful individuals. Here is my problem.
I am in a middle of a project using AVRs and BASCOM. I have to communicate with 2 or 3 remote devices, AVRs/BASCOM. I figured the best way to do this is via RS485. However, I have to reuse existing lines/wires which are #16 or 18 wires, but are not twisted. I understand "twisted" is important for RS485 to cancel noise, can I use non twisted wires? The distance of the other devices is about 300 to 400 meters away, the wires are enclosed in rigid conduits, with multiple wires running with it. I suppose some are carry AC supply. What would be the best option to have a reliable communication without the twisted pair? Rewiring is not an option and I have to make do with the existing wires.
I've googled around and found a 20ma loop serial communication which may work, but the speeds are limited, with link below. Will this be a better option?
http://www.bb-elec.com/tech_articles/current_loop_app_note/basics_of_current_loop.asp |
|
Back to top |
|
|
i.dobson
Joined: 05 Jan 2006 Posts: 1570 Location: Basel, Switzerland
|
Posted: Wed Feb 21, 2007 2:25 pm Post subject: |
|
|
Hi,
What sort of speeds are you looking at?
I've run RS485 over all sorts of different wires, and not all of them were twisted. If you can get away with 9600 baud I can't seen any problems.
Regards
Ian Dobson _________________ Walking on water and writing software to specification is easy if they're frozen. |
|
Back to top |
|
|
ATIU
Joined: 15 Oct 2004 Posts: 534
|
Posted: Wed Feb 21, 2007 2:42 pm Post subject: |
|
|
9600 bps is enough for my application. How far/long were the wires in your application? Can this be in the same conduit with supply lines (220V/60HZ)? Thanks for your quick reply. |
|
Back to top |
|
|
ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
|
Posted: Wed Feb 21, 2007 2:55 pm Post subject: |
|
|
Quote: | 9600 bps is enough for my application. How far/long were the wires in your application? |
i just installed RS485 network to communicate 3 pcs of remote oil filling machine with a computer using my own made transceiver using SN75176 and MAX232 in full duplex mode (the remote machine support it ).
the speed is 19200baud and everything is ok
the length of the cable i use is 500m with STP for RF interference protection. it should be no problem using AVR |
|
Back to top |
|
|
i.dobson
Joined: 05 Jan 2006 Posts: 1570 Location: Basel, Switzerland
|
Posted: Wed Feb 21, 2007 3:15 pm Post subject: |
|
|
Hi,
I mainly use PC's connected to several particle counters using a RS485 network. Cable lengths are usually only afew meters for a rack mount or 100-150metres for a building installation.
I've actually found that the number of devices on the bus makes a bigger difference than the length of the cable. I have one site where they are running 20 devices on the bus and the cable is about 100meters and there we had to replace the cable with twisted pair.
On another site the cable is about 250meters long in total but only has 4 devices on it and there we use "normal data cable" (el'cheapo serial cable) without any problems. Both sites are running the same software/communication cards/end devices.
If possible use shielded/twisted pair cable for the minimum number of problems but RS485 is designed for an industrial environment so it should handle interference better than RS232.
Regards
Ian Dobson _________________ Walking on water and writing software to specification is easy if they're frozen. |
|
Back to top |
|
|
ATIU
Joined: 15 Oct 2004 Posts: 534
|
Posted: Thu Feb 22, 2007 1:05 am Post subject: |
|
|
Thanks for the replies. I will probably go with the 20ma loop because of its inherent opto isolation and I am not comfortable using RS485 without twisted pair bus lines. |
|
Back to top |
|
|
Antony(uk)
Joined: 26 Jun 2006 Posts: 275 Location: Devon UK
|
Posted: Fri Feb 23, 2007 3:42 pm Post subject: |
|
|
Hi
A question request for EX4 or Ian D or anyone out there please.
I have built 2 RoV's and modifying the second one to get better depth and pressure.
I need help on the Hardware from my mega 8535 down to another mega 8535 chip. The base of the commutations software was done by Ian Dobson some time ago and I have modified it a lot.
But the hardware is something I am no good with .
Is there any chance of a schematic/drawing etc on how you did the hard wiring.??
I am completely rebuilding the electrinics inside both the controller and the RoV.
Regards Antony(UK) |
|
Back to top |
|
|
ex4
Joined: 13 Jan 2006 Posts: 1062 Location: indonesia
|
Posted: Mon Feb 26, 2007 3:17 am Post subject: |
|
|
Quote: | s there any chance of a schematic/drawing etc on how you did the hard wiring.?? |
this is my converter schematic
|
|
Back to top |
|
|
|