Communicating with an Arduino that is relatively far away

Using 4 would work I guess :slight_smile:
I'm having a bit of trouble finding a local source for the low speed full duplex versions but the MAX3082E seems to do what I want so I just need 4 of them then.

So if I'm getting this straight this is how I would hook this up:
For the local TX to remote RX:
Local side: DE to Vcc/+5V, DI to TX.
Remote side: RE to Vcc/+5V, RO to RX.
Local A to remote B, local B to remote A. And a resistor between A and B on both sides.
A 0.1 uF condensor between Vcc and +5V, and GND to ground obviously.

nicov:
Using 4 would work I guess :slight_smile:
I'm having a bit of trouble finding a local source for the low speed full duplex versions but the MAX3082E seems to do what I want so I just need 4 of them then.

So if I'm getting this straight this is how I would hook this up:
For the local TX to remote RX:
Local side: DE to Vcc/+5V, DI to TX.
Remote side: RE to Vcc/+5V, RO to RX.
Local A to remote B, local B to remote A. And a resistor between A and B on both sides.
A 0.1 uF condensor between Vcc and +5V, and GND to ground obviously.

Well you really need to show four chips wired to two separate cable pairs. One the local side one chip (for the local's transmit signal) has DE wired to Vcc and RE wired to Vcc, and DI wired to serial tx pin. The other local chip (for the receive signal) has it's DE wired to ground and RE wired to ground and it's RO pin wired to arduino rec pin. The remote has a similar setup as long as you keep in mind the direction of data flow through each seperate cable pair. And yes, four 150 ohm resistors wired from A to B on all four chips. And good on remembering about the benefits of bypass caps at the Vcc pins to ground for all four chips. Does that help? English is a poor method to talk electronics as a schematic drawing is the true language of electronics. :wink:
Lefty

Local A to remote B, local B to remote A

All As together and all Bs together. Have a look in the data sheets, they always have examples.

And a resistor between A and B on both sides.

Correct.


Rob

I will try and draw a schematic, but knowing my drawing skills I'm afraid it might not make things a whole lot clearer :wink:

So A goes to A and B goes to B. The datasheet did have an example but it was a bit unclear to me how they were supposed to be connected because the schematic showed the wires as being twisted and I couldn't figure out what went to what.

Here we go... This is the first time I've ever used Eagle or drawn a schematic and I can't say that I really know what I'm doing :wink: So I'm guessing it's not going to be all that great. I found the drawing process a bit frustrating so I only did one side for now.

Does that look like it would work? Or do I need to connect the unconnected pins to something too?

C1 and C2 look suspicious.

I thought so too.. But the example schematic was a bit unclear again to a schematic noob like myself.

This is what's in the datasheet:

If they didn't mean what I had in the previous schematic, how is this one?

That looks better (the capacitors; someone else will have to comment on the rest).

RE is active low, on the right-hand chip it's pulled high.


Rob

Graynomad:
RE is active low, on the right-hand chip it's pulled high.


Rob

Aha, thanks for that hint! I thought something might be up with it, with the slash after the name or the "overscore". Learning by doing, I guess :wink:
So I need to connect it to ground on the right side one then.

I found this table in the datasheet:

So on the left side, RE can be disconnected, DE to VCC.
On the right side, RE to GND, DE can be disconnected.

Like this?

On the remote end you really should ground pin 3, DE, to make sure it's transmit driver is forced off into tri-state mode.

Lefty

retrolefty:
On the remote end you really should ground pin 3, DE, to make sure it's transmit driver is forced off into tri-state mode.

Lefty

According to the table it shouldn't care but I guess better safe than sorry :wink:

Version 4 then:

the slash after the name or the "overscore"

Also the small circle on the graphic, on chips that means an active low or inverted signal.

Just some notes about schematic layout.

If you mirror image the remote chip the drawing will be a lot clearer.

When things are tied to power rails it's almost always better (clearer) to have VCC going up and GND going down. Your caps go up.

Most beginners make a real dog's breakfast by running the GND wire to every possible place. You haven't done that which is good, in this case however I would argue that because these chips are physically remote from each other you should draw the GND line between the two to reinforce that they have to have a common GND and that that is formed by a GND wire in the cable.


Rob

Thanks for the helpful hints Rob, I appreciate it!

How do you like this? It does look a lot clearer :slight_smile:

Graynomad:

the slash after the name or the "overscore"

Also the small circle on the graphic, on chips that means an active low or inverted signal.

Just some notes about schematic layout.

If you mirror image the remote chip the drawing will be a lot clearer.

When things are tied to power rails it's almost always better (clearer) to have VCC going up and GND going down. Your caps go up.

Most beginners make a real dog's breakfast by running the GND wire to every possible place. You haven't done that which is good, in this case however I would argue that because these chips are physically remote from each other you should draw the GND line between the two to reinforce that they have to have a common GND and that that is formed by a GND wire in the cable.


Rob

Actually these don't require a common ground between the local and remote chips, that is one of the advantages of the A/B signals being a true differential signal pair. I'm sure some will disagree with this, but I would say hold off until you actually test such a link using independent power sources at each end, it will continue to work without a common ground wire between the pair.

Lefty

Your probably right, but I'm kind of a belt and suspenders kind of guy and like to hardware the control signals when I know they are never going to be switched.
Lefty

Welcome to the world of conflicting opinions Nico. This is one of the common dichotomies like Canon/Nikon, Ford/GM etc.

I have experience with RS-485 but Lefty has made a career of using it in very bad environments, so I'll bow to him on this while retaining the right to differ :slight_smile:

IMO the schematic is much clearer now.


Rob

Thanks guys, really appreciate your input! :slight_smile:

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.

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?