noise in rs-485 communication channel

[bikas.bikun]

Dear all i have a problem .

in my project i have 5 nodes interconnected with RS-485 channel, and all nodes have one switches when switch is pressed then controller pin goes low and master performs the operation.

it was good at testing,but at validation controller gets trigger automatically without pressing the switch.so what could i take care of ?
>all my nodes are within 20-25 cm of a 440V supply

 

[hamed8419215]

for RS485 you should use Twisted Pair wires. in other word the two wires should not separate from each other.

---------- Post added at 07:45 ---------- Previous post was at 07:44 ----------

Also you should use Termination Resistor at the two ends of your RS485 line.

---------- Post added at 07:48 ---------- Previous post was at 07:45 ----------

I think that your problem is not related to RS485.

---------- Post added at 07:49 ---------- Previous post was at 07:48 ----------

Because the switch controls operation of nodes rather than RS485.

 

[eepty]

Bikas, you mean when a switch of a node is pressed, the node's controller pin goes low and send a package to the master, right?

How you test the system?

I think 25cm is really a short distance for RS485 and should not have much problem on noise issue. In fact I have tried to use simple non-twisted non-shielded wires for RS485 for similar distance with no problem.

 

[bikas.bikun]

for RS485 you should use Twisted Pair wires. in other word the two wires should not separate from each other.

---------- Post added at 07:45 ---------- Previous post was at 07:44 ----------

Also you should use Termination Resistor at the two ends of your RS485 line.

---------- Post added at 07:48 ---------- Previous post was at 07:45 ----------

I think that your problem is not related to RS485.

---------- Post added at 07:49 ---------- Previous post was at 07:48 ----------

Because the switch controls operation of nodes rather than RS485.

My nodes are at least 30 meters apart from each other ,but a 440V supply cable is parallel to my rs-485 cable.

 

[hamed8419215]

In 30 meter you should not have any problem (although with bit rate of less than 512Kbps).
for more information about RS485 see: "Interfacebus.com"

 

[bikas.bikun]

for RS485 you should use Twisted Pair wires. in other word the two wires should not separate from each other.

---------- Post added at 07:45 ---------- Previous post was at 07:44 ----------

Also you should use Termination Resistor at the two ends of your RS485 line.

---------- Post added at 07:48 ---------- Previous post was at 07:45 ----------

I think that your problem is not related to RS485.

---------- Post added at 07:49 ---------- Previous post was at 07:48 ----------

Because the switch controls operation of nodes rather than RS485.

Definitely you are right,switch controls the operation of nodes,so i think this is a n issue of noise,So what should i do ?

 

[hamed8419215]

You should decrease Pull up(or pull down) resistor. inserting a little capacitor in parallel with switch also improves noise immunity.
Also you can sense "State" of switch instead "Transition" of switch.