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Topic: Communicating with an Arduino that is relatively far away (Read 4 times) previous topic - next topic

retrolefty


Thanks guys, really appreciate your input! :)

One more question then. Over here, Icc is specified as 0.375 mA typical, the PDF datasheet I have says max 1.000 mA. So I assume it will be safe to power the chips from the Arduinos 5V if the local Arduino is USB powered?


Certainly.

radman

Quote
I have experience with RS-485 but Lefty has made a career of using it in very bad environments


Why use RS485 though rather than RS422 if there is no need to multidrop?

Graynomad

I don't think it matters here. 485 has better common-mode voltage specs, and I think the chips are easier to find and there's a larger range, but either is good I think.

_____
Rob
Rob Gray aka the GRAYnomad www.robgray.com

retrolefty

Yes either can be made to work as long as the driver chip on one end is the same 'flavor' as the receiver chip at the other end.

By the way Wikipedia shows a good three resistor termination method one can use on the receiver end of each path (if using two pair full duplex) which will ensure no false data hits due to noise in case the far end of a link is powered off, it's shown in the first picture showing a series 680 ohm, 120 ohm, 680 ohm resistors wired to the recievers Vcc and ground and A and B signal pins. Good idea.

http://en.wikipedia.org/wiki/EIA-485

Lefty

Nico V

#39
Feb 28, 2013, 10:25 pm Last Edit: Feb 28, 2013, 10:27 pm by Nico V Reason: 1
I finally got around to finishing this up.. And wanted to update the thread with some findings.
The first is that the remote/RX end pin 3/DE must in fact be grounded. I just got garbage if I didn't ground it.
The other is that B on one end must be connected to B on the other end, and A to A. Connecting B to A and vice versa also gave garbage.
It seems to work fine without the resistors too, but I assume that may change with longer distances so I put them there anyway.
Figured this stuff might be good to know.

The chips I'm using are MAX3082E. Amazingly everything worked as expected the first time I connected it, I had to actually disconnect some stuff to make sure it wasn't just the software fooling me ;) This weekend we'll test with a longer cable in between.

Thanks again for all the help!

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