AVR-Chat

--- Chuck Hackett <egroupscdh@WhiteTrout.net> wrote:

> I would like to transfer data some distance (100
> feet in one case, 400 feet in
> another) between AVRs and I'm looking for the least
> complex, least expensive way
> to accomplish this.  Environment:
> 
> 1) Using facilities available on AVR processors
> (such as UART, TWI, etc.)
> 
> 2) I have cable in the ground which is Telco grade,
> gel filled, direct bury
> cable with 6 twisted pair
> 
> 3) Speed is not critical.  Of course I'd like to go
> as fast as possible but I'm
> willing to sacrifice speed to keep complexity/cost
> down ... Well, I'd rather not
> go back to the 110 bps days!  :-)
> 
> 4) Multimaster is desirable
> 
> I'm thinking that the solution will use some king of
> differential driver.
> 
> I was doing some reading about TWI but it's unclear
> to me if this works in this
> situation.  The only thing I could find about
> distance limits was that the bus
> capacitance must be below 400pf but I don't know the
> capacitance of my cable ...
> 
> BTW:  I think this forum is appropriate for this, if
> not, please let me know.
> 
> Suggestions?
> 
> Cheers,
> 
> Chuck Hackett
> "Good judgment comes from experience, experience
> comes from bad judgment"
> 7.5" gauge Union Pacific Northern (4-8-4) 844
> http://www.whitetrout.net/Chuck
> 
> 
> 
> 
Hi;

as I know (using Siemens documents) if you use RS232
(using MAX232) the distance is limited to 100 feet.
but Siemens also offered some other solutions:

signalling   noise-prtction dist(feet)   max-speed
----------------------------------------------------
RS232        somehow        100          9600
RS485        somehow        1500         9600
RS422        good           3500         upto 19200
CurrentLoop  best           3500         max of 9600

note: Siemens calls RS232 as V24, RS422 & RS485 as X27
and CurrentLoop as TTY.

in a very noisy environment the best solution is using
current loop (4, 20mA) one node in Active (current
generator) and the other in Passive (current
switcher/detector) mode.

but in steel making factory which I'm working, they
use commonly RS422(Siemens:X27) in low noise
environments, and CurrentLoop or TTY in high noise
env.

ofcouse you can make a network with these links. but
for RS422/X27 there is a limitation of 32 partners on
each link without repeater. for some applications see:

www.rs485.com

and see Texas Instruments products for RS422
interfacing.

otherwise if the environment is too noisy and you can
pay more money, there is some fiber_optic-RS232
switchs (eg: ADAM serias made by Advantech). or some
wireless equipments (upto 20miles, with a speed of
115K bps) but is very expensive.

good luck.
(and excuse me for poor english!)




		
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