Good quality cable needed

[Normnet]

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.
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:

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.

Also One wire serial comms on +5V line from the master Melanie.


Norm

[NickMu]

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

[Ioannis]

You might also consider PoE that are cheap devices and use standard RJ-45 sockets.

Ioannis

[NickMu]

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

[NickMu]

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