I don't know much about RS485 but I did read that the current return path
is required. You should be able to send and about 100K up to 4000 feet.
I'd use a section of Eithernet cable because I know it is twisted inside.
I don't know the best way to provide a "return path for all voltages"
If this is going through optical isolators,I see a problem the signal
voltages are like RS232 −7V to +12V. The optos are going to do 0 to 5
volts with is usually very marginal.
On Thu, Dec 31, 2020 at 8:05 PM Gene Heskett <[email protected]> wrote:
> On Thursday 31 December 2020 20:10:35 Chris Albertson wrote:
>
> > Now is the time to connect the digital scope and see what is actually
> > on the wire. Is the data bad or is the receiver unable to read good
> > quality 38400b data?
> >
> > This is differential data, it should be able to go half a kilometer or
> > something like that. Is it actuary using a twisted pair of wires and
> > is there a good logic ground?
> >
> That I doubt. Its a 2 wire cable, so any logic ground is coming thru
> other cable from the 5i25, thru the interfaceing and back to the ACM
> terminal. DCM could be grounded but is not, and everything on that
> circuit isvia the opto's isolating the spindle outputs of the 7i76D.
>
> That stuff is still hooked up, but could be disconnected as its no longer
> actually controlling the motor. There does not appear to be a ground
> reference for the rs485 signals called out in the sample wiring diagram.
> There is an earth ground in addition to the 2 wire single phase input,
> and its connected back to the static ground in the service box.
>
> > It's easy to see if the cable is the cause. look at the bits on the
> > cable end, then remove the cable and look at them in the output port.
>
> The only way I can access that would be to back the pins out of the term
> strip far enough to put the scope probe hook onto the Hilitchi pin. The
> scope is plugged into a different circuit entirely, so its ground
> reference is bound to have some noise on it. I can set the scope to
> combine the 2 signal wires into a differential, but having done that,
> the serialization of the samples quantizations can easily be seen. I
> should probably do that, if for no other reason than to confirm the baud
> rate matches going both ways. I have previously caught the pc lying
> about the actual baud rate its generating. Depending on the individual
> driver, it might be fixeable but haven't tried. From an lsmod:
> usbserial 31410 3 ftdi_sio
> and I've not had previous experience with the ftdi_sio being off.
>
> Since the lags can be gotten used to, I might just leave it at the slower
> speed as that seems to be bulletproof so far.
>
> Thanks Chris. And a Happier New Year to all.
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> If we desire respect for the law, we must first make the law respectable.
> - Louis D. Brandeis
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>
>
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--
Chris Albertson
Redondo Beach, California
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