RS485 Extender

[SergioRM]

Hi all,

I'm starting using PIC and RS485 (I'm using SN75176 driver). This chip is able to transmit data up to 32 devices in the network. I'm think about make an extender to more than 32 devices using in the end of line two RS485 drivers "back to back". Will this work? Anyone have tried it or have another idea? (I can use MAX487 to 128 nodes, but it's 10X more expensive than SN)?

Best Regards,

Sergio

[mister_e]

Hi sergio,

Tought here, change your electronic supplier... go at www.digikey.com and see the price difference between those two device

MAX487CPA : 3,87 $ USD
SN75176BP : 0,93 $ USD

far from 10X.

If you're going to say that you can drive 128 node with 650 uA of current drive those do also the job

MAX483CPA :650uA
DS485 :900uA
SN75LBC176P : 1.5mA
SN65LBC176P : 1.5ma

and such.

[SergioRM]

Hi Steve,

Thanks for your aswer. I live in Brazil, and here we have 10X of diference between this IC's.

Other problem is the delivery time. SN75 we have in many suppliers, but for Maxim IC's we wait until 45 days to delivery...

I request some samples of DS1487. It can drive 128 nodes and the price is 1/2 of MAX487. It can solve my problem.

But I still want to know if we can make a repeater connecting "back to back".

Best Regards and Happy New Year !!!

[Dick M]

[QUOTE]Originally posted by SergioRM
[B]Hi Steve,
But I still want to know if we can make a repeater connecting "back to back".

Yes you can connect two 75176 back to back for a level booster if you are only sending data in one direction. If you are doing two wire duplex then you would have to have some kind of switch in your repeater to detect the source of the data and switch the direction of the repeater.