multi point & long distance rs485 half duplex

[mohammad hassanzade]

hi all guys
i design a system for control a large greenhouse & i want use rs485( max485 chip) .
in this design exist:
1-1 master & 30 slave
2- distance from master to last slave is 1km
question:
1- can the max485 to this services ?(distance with this number master/slave)
2- how i can design this circuit for distance longer than 1km ? (for example 20km)
guide :
1-i don't use another system, because this system is cheap for me :razz:
2-because the rs485 used to maximum 1.2km distance help to me to amplify signal for longer distance.(for example 20km)
thanks a lot

 

[john blue]

2- how i can design this circuit for distance longer than 1km ? (for example 20km)
You can use another max485 as a repeater in between. It will amplify the signal after 1km.

guide :
1-i don't use another system, because this system is cheap for me
2-because the rs485 used to maximum 1.2km distance help to me to amplify signal for longer distance.(for example 20km)

 

[mohammad hassanzade]

thanks john
john : You can use another max485 as a repeater in between. It will amplify the signal after 1km.
i want found a cheap way for this issue but this proposal is good
can do you show to me this configuration ?
can do you help me for another question?
thanks

 

[john blue]

can do you help me for another question? Sure

---------- Post added at 17:28 ---------- Previous post was at 17:18 ----------

 

[mohammad hassanzade]

good
but for repeater circuit, we need control DE or RE for in/out function & for this work we need a micro controller but this way not a cheap way
how can i found a cheap way for this issue
thanks a lot for your help

---------- Post added at 22:35 ---------- Previous post was at 21:07 ----------

hi all and john
i googled for this issue & i found a circuit
this is an application notes from maxim & wrote for rs-422
please see this & reply my question
View attachment rs485-repeater.PDF
1- this circuit work carefully & correctly? (i see this & i guess this work correctly)
2- can this circuit work for rs485?

 

[Kurenai_ryu]

it's the cheapest way... to set a microcontroller with 2 max487 as a bridge.... other ways are more expensive....

 

[arbj]

are you sure this is cheap, what about the cost of a 1 km (I am assuming the shortest length is 1 Km) long wire, also add the maintenance that may be required from time to time, there may be some problems like rats/animals chewing wires, water getting into wires etc.

 

[john blue]

Depends. You can use wireless module to solve the problem. But, the module itself cost a lot.

**broken link removed**.

 

[mohammad hassanzade]

thanks a lot for your help

i think this schematic a cheap way & really correctly.
i hope use this way for project but test this way
if failure to a good replay,i sure use a micro controller for this issue
i think attiny2313 a good micro controller that have two interrupts
i happy ,if have any proposal & give me

i'm sorry for being weak in english
with a lot thanks
mohammad hassanzade