Hello friends,
I'm having a problem on arduino serial communication. I need to establish multi drop serial network for about 300 - 400 meters. Is it possible to use MAX485 with twisted pair lines?
I am confused as am newbie in this regards.
If it's not possible, please suggest me a reliable way...
your help is highly appreciated.
Thank you
RS485 I think is good for 1000 meters, if properly terminated.
AN723 RS485 fail safe terminations.pdf (155 KB)
AN763 RS485 termination.pdf (234 KB)
AN-960 Analog Devices RS485.pdf (246 KB)
Thanks for getting back to me,
Is it possible to cover that distance when we use MAX485 since it works in 5V?
Renaz:
Thanks for getting back to me,Is it possible to cover that distance when we use MAX485 since it works in 5V?
yes, as long as you wire it as a bus with short stub lengths, and terminate each end of the bus.
Basically you need 3 wires, A,B, and GND. I have used CAT5 with no issues. I use 4 pair CAT5e 1,2=A,B 4,5=GND, 3,6=second Channel A,B 7,8=remote Power +12v.
I use 120 ohm terminators at each end of the link, I wire it with one set of pullups/pulldowns 680ohm as a fail safe configuration:
+5v<->680ohm<->A<->120ohm<->B<->680ohm<->GND at the Master end,
A<->120ohm<->B at the end Slave.
My RS485 devices use 2 RJ45 sockets, one in, one out. this makes my stub length less than 1 inch(from Socket to MAX485 or SN75176) for each device. each device has a jumper selectable termination. Only the Master and Last Slave have the termination enabled. This allows me to use standard CAT5E patch cables. (EIA/TIA 568B wiring). As long as I don't plug my RS485 network into a 1gb Ethernet port every thing is happy :). Standard 10,100mb ethernet only use 1,2,3,6
As a secondary ground fault protection I place a 100 ohm resistor between 4,5 and my device ground to limit ground loop fault currents.
Chuck.
Thank You Mr Chuck. I really appreciate it.
I'll try it out 