RS-485, Long Distance Control Question!!!
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Posts: 46,084
I am in the middle of a project for a remotely operated device (cable
300+') that I thought would be an ideal project for RS-485. The
control consists of a command via switches at the controls (master)
then action at the device (slave). When I got started I thought this
would be relatively easy....but I have not had any luck getting a
command to work even though the debug screen indicates that the comms
are good (at the master). I put a debug line in the slave and when
you hook the serial cable to the slave the comms indicate "bad".
Beig relatively new at the electronics game (more a mechanic), this
has proved very frustrating.
Any ideas? Am I making this simple task harder then it needs to be
by introducing the RS-485. By the way I am using example code and
electronis configuration from Scott Edwards Book (LTC1487 chipset).
I would appreciate any thoughts.
Scott
300+') that I thought would be an ideal project for RS-485. The
control consists of a command via switches at the controls (master)
then action at the device (slave). When I got started I thought this
would be relatively easy....but I have not had any luck getting a
command to work even though the debug screen indicates that the comms
are good (at the master). I put a debug line in the slave and when
you hook the serial cable to the slave the comms indicate "bad".
Beig relatively new at the electronics game (more a mechanic), this
has proved very frustrating.
Any ideas? Am I making this simple task harder then it needs to be
by introducing the RS-485. By the way I am using example code and
electronis configuration from Scott Edwards Book (LTC1487 chipset).
I would appreciate any thoughts.
Scott
Comments
I don't have any experience with RS-485 so I can't give you specific
help, but I have read alot of information on it and have some
schematics and so forth on disc. One configuration I have a
schematic for shows a Maxim MAX-232 interface with a 75176B RS-485
transceiver. I am not sure if this is the same as your hardware
setup or not. One place that has alot of information on this subject
is: http://www.melabs.com/resources/links.htm
Scroll down to where it says RS-422 and RS-485. There are atleast a
dozen links about RS-485 setups and troubleshooting.
Hope this helps!
--- In basicstamps@yahoogroups.com, "njmadeb <MADEB@p...>"
<MADEB@p...> wrote:
> I am in the middle of a project for a remotely operated device
(cable
> 300+') that I thought would be an ideal project for RS-485. The
> control consists of a command via switches at the controls (master)
> then action at the device (slave). When I got started I thought
this
> would be relatively easy....but I have not had any luck getting a
> command to work even though the debug screen indicates that the
comms
> are good (at the master). I put a debug line in the slave and when
> you hook the serial cable to the slave the comms indicate "bad".
> Beig relatively new at the electronics game (more a mechanic), this
> has proved very frustrating.
>
> Any ideas? Am I making this simple task harder then it needs to be
> by introducing the RS-485. By the way I am using example code and
> electronis configuration from Scott Edwards Book (LTC1487 chipset).
>
> I would appreciate any thoughts.
> Scott
You need to be more specific about your circuitry. 300' (about 100m)
is definitely not trivial event with RS485. And a basic stamp is
not exactly an RS485 device.
Did you project work whith a short cable of 3' (1m) or so?
Shielding and signal grounds want to be carefully separated in cases
as the one you describe. The type of cable (two separately twisted
pairs of stranded wire plus shield) really matters here. Ends may need
to be properly terminated to avoid reflections.
That's just some basic hints.
Regards
Adrian
pair of MAX485's and standard twisted pair phone cable. Max speed was 9600
baud.
Original Message
> I am in the middle of a project for a remotely operated device (cable
> 300+') that I thought would be an ideal project for RS-485. The
> control consists of a command via switches at the controls (master)
> then action at the device (slave). When I got started I thought this
> would be relatively easy....but I have not had any luck getting a
> command to work even though the debug screen indicates that the comms
> are good (at the master). I put a debug line in the slave and when
> you hook the serial cable to the slave the comms indicate "bad".
> Beig relatively new at the electronics game (more a mechanic), this
> has proved very frustrating.
>
> Any ideas? Am I making this simple task harder then it needs to be
> by introducing the RS-485. By the way I am using example code and
> electronis configuration from Scott Edwards Book (LTC1487 chipset).