Your diagram doesn't provide sufficient detail - you should do a Google search on "RS485 repeater" which is what you really need where your diagram shows an optoisolator.
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Your diagram doesn't provide sufficient detail - you should do a Google search on "RS485 repeater" which is what you really need where your diagram shows an optoisolator.
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I've seen networks using 75176 chips with up to 99 nodes. The data rate was slowed down to 1200 baud, and they were wired with good quality twisted pair wire, properly terminated. There are newer chips that will allow 128 nodes at much faster data rates, however if your data packets are small you might find slow baud rates are just fine.
Jerry.
If your oscilloscope costs more than your car...
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As always, do choose the right tool for the job. 75176 chips are for 32 nodes and nobody will take the blame if your data are lost on an overloaded network.
As shown on a previous post there are more recent chips that do 256 nodes. Price is very good, so why challenge your luck?
If you insist on using the ancient (but reliable I have to admit) 75176 then do place a repeater after 30 nodes an extentd the network another 30 nodes and 1200 meters. I would place a dedicated chip for transmit and another one for receiver, forgeting the auto switch between the Tx/Rx lines. You are going to place a UTP/FTP cable, so there are free pairs to use as dedicated Rx/Tx lines.
Ioannis
Last edited by Ioannis; - 25th November 2008 at 10:38.
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