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RS232 expander?

A

Abacus-Ri

Jan 1, 1970
0
Hi to all,
I'm searching for help regards RS232 output multiplier. Unit should consist
RS232 input (opto isolated) and minimum 12 outputs.
Any help will be appreciated.

Damir
 
S

scada

Jan 1, 1970
0
Abacus-Ri said:
Hi to all,
I'm searching for help regards RS232 output multiplier. Unit should consist
RS232 input (opto isolated) and minimum 12 outputs.
Any help will be appreciated.

Damir

RS232 is not intended to communicate to more than one device at a time. You
can convert the RS232 to RS485 which is designed to handle multiple
communications.
 
J

James Meyer

Jan 1, 1970
0
RS232 is not intended to communicate to more than one device at a time. You
can convert the RS232 to RS485 which is designed to handle multiple
communications.

And what happens if I do exactly what "Abacus-Ri" wants to do? Do I get
a late night visit from the RS-232 police?

Jim
 
S

starfire

Jan 1, 1970
0
That's not what he asked for...

If you're trying to drive several RS232 receivers from a single RS232
source, just receive the single RS232 with a MAX232 (convert it to TTL),
optoisolate the signal, then send the TTL input to 12 separate MAX232
drivers. Depending on the RS232 driver you choose, be careful to observe
total input loading. If you need to, use a buffer after the optoisolation.
Also make sure you observe polarity.

Dave

 
D

dont know

Jan 1, 1970
0
Abacus-Ri said:
Hi to all,
I'm searching for help regards RS232 output multiplier. Unit should
consist RS232 input (opto isolated) and minimum 12 outputs.
Any help will be appreciated.

Damir

do you mean a unidirectional hub?
one rs232 input feeds 12 rs232 outputs?
you have to make one yourself!
 
A

Abacus-Ri

Jan 1, 1970
0
Hi to all,
Just to be clear, I plan to build RS232 repeater with just one source. I
need it to connect navigation equipment to one gyro compass(3x radars, 2x
communication antennas, 2x Inmarsat B, 2x Inmarsat A, 2 reference receivers
and some spare)...

thanks,
Damir



 
C

CFoley1064

Jan 1, 1970
0
Subject: Re: RS232 expander?
From: "Abacus-Ri" [email protected]
Date: 6/14/2004 8:48 PM Central Standard Time
Message-id: <[email protected]>

Hi to all,
Just to be clear, I plan to build RS232 repeater with just one source. I
need it to connect navigation equipment to one gyro compass(3x radars, 2x
communication antennas, 2x Inmarsat B, 2x Inmarsat A, 2 reference receivers
and some spare)...

thanks,
Damir




Hi, Damir. As with most projects of this type, "the devil is in the details".
Obviously, if you have bidirectional comm, you can only talk with one
instrument at a time. And with different types of instruments, you almost
certainly are going to have different command sets to deal with. I've done
this before several times with PCs and RS-232 instruments. In one case, I had
three each of two different types of instruments (three load cell interfaces
and three conductivity meters). They all had RS-232 ports, and I had a
limitation of only being able to use one computer controller serial port for
bidirectional communication with all six.

I examined the interfaces, and found that one type of instrument had only
XON-XOFF software handshaking, and the other had RTS and CTS hardware
handshaking. That limited me to a maximum of four lines to switch (TxD, RxD,
CTS, RTS). Since this was an industrial application and I wanted to keep it as
simple as possible (the elegant technical solution and the people solution are
sometimes wildly divergent), I chose 6 ea. 5VDC coil 4PDT telecomm relays,
which are made for switching signal level voltages and currents. I also used
pulldown resistors on the instrument side of the controller's port outputs (TxD
and CTS), which made those signals inactive when another relay was active.
This permitted me to poll each of the six instruments for data every so often,
with minimal overhead for hardware, maximum simplicity, and total transparency
for the instruments not in on the conversation -- they just thought the lines
were inactive whenever their relay wasn't switched on. The only non-trivial
part was reprogramming the UART for switching between software handshaking and
hardware handshaking, and changing baud rates. The end product looked
something like this (view in fixed font or M$ Notepad):


TxDo---o------------o
| RY1 __--o--------oRxD
| -o-. ___
| '--|___|-12V
RxDo---|-o----------o 4.7K
| | RY1 __--o--------oTxD
| | -o
| |
CTSo---|-|-o--------o
| | | RY1 __--o--------oRTS
| | | -o
| | |
RTSo---|-|-|-o------o
| | | | RY1 __--o--------oCTS
| | | | -o-. ___
| | | | '---|___|-12V
| | | | 4.7K
o-|-|-|------o
| | | | RY2 __--o--------oRxD
| | | | -o-. ___
| | | | '---|___|-12V
| o-|-|------o 4.7K
| | | | RY2 __--o--------oTxD
| | | | -o
| | | |
| | o-|------o
| | | | RY2 __--o--------oRTS
| | | | -o
| | | |
| | | o------o
| | | | RY2 __--o--------oCTS
| | | | -o-. ___
| | | | '----|___|-12V
4.7K
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


Each case is different, and there aren't many rules for this type of thing
except get it to work reliably. Assuming you can tie the GNDs of the
instruments together, you could probably also do this with a level translator,
a data selector or decoder IC, NAND gates and a handful of transistors, too.
Just think about what you actually need, and describe the problem to yourself
well. The rest should be easy.

Oh, yes. If this is actually going out on the water, watch for salt spray --
it kills electronics without mercy, unless you've got full metal jacket
protection..

Good luck
Chris
 
T

Tim Shoppa

Jan 1, 1970
0
Abacus-Ri said:
Hi to all,
Just to be clear, I plan to build RS232 repeater with just one source. I
need it to connect navigation equipment to one gyro compass(3x radars, 2x
communication antennas, 2x Inmarsat B, 2x Inmarsat A, 2 reference receivers
and some spare)...

If the protocols are compatible (i.e. devices are uniquely addressable and
always work as the slave in a master-slave arrangement) then it's just a
matter of treating RS232 as a bus (which really it isn't, but a couple
of diodes go a long way to getting there).

If the protocols are not compatible or the devices talk whenever they feel
like it then you want a "serial multiplexer"... type it into Google and
look at what you get. If all your devices are
NMEA (which they may be) then there are some off-the-shelf products
that do this all with very little pain. If you have some that aren't
NMEA then there are still solutions, but they will require some extra
software on the single-RS232 side.

Tim.
 
R

Repzak

Jan 1, 1970
0
If the protocols are not compatible or the devices talk whenever they feel
like it then you want a "serial multiplexer"... type it into Google and
look at what you get. If all your devices are
NMEA (which they may be) then there are some off-the-shelf products
that do this all with very little pain. If you have some that aren't
NMEA then there are still solutions, but they will require some extra
software on the single-RS232 side.


"standard" nmea signals are 0-5V ....

if it is the case, then just use a TTL buffer....

Or put a Max232 in the frontend and some TTL buffers on the output....

if i remember right nmea uses open collector output, so 7407 could be a
winner :)

Kasper
 
S

starfire

Jan 1, 1970
0
The NMEA0183 interface from my Garmin E-Trex Vista is RS232.

Depending on the installation, TTL NMEA0183 code may be available before
going to the RS232 converter, though.

I have no idea what the "standard" NMEA interface levels are.

To the original question, though, if bi-directional serial interfaces are
required, some sort of multiplexer will be needed or a very well controlled
architecture to make sure the outputs don't walk on each other.

This sounds like an interesting microcontroller project, though...

Dave
 
L

Leon Heller

Jan 1, 1970
0
Abacus-Ri said:
Hi to all,
I'm searching for help regards RS232 output multiplier. Unit should consist
RS232 input (opto isolated) and minimum 12 outputs.
Any help will be appreciated.

Where I used to work we designed a 'comms hub' that connected a number of
RS-232/RS-422 devices to a PC. It used a mid-range PIC connnected to a
number of Atmel AT90S2313s via SPI. It worked very well.

Leon
 
W

Wouter van Ooijen

Jan 1, 1970
0
I'm searching for help regards RS232 output multiplier. Unit should consist
RS232 input (opto isolated) and minimum 12 outputs.

What's the problem? Use a fast optocoupler as isolation, 1489/1488 as
level converters. For 12 outputs I would not bother with max232's,
just get a +/- 10 Volt supply.


Wouter van Ooijen

-- ------------------------------------
http://www.voti.nl
PICmicro chips, programmers, consulting
 
R

Repzak

Jan 1, 1970
0
To the original question, though, if bi-directional serial interfaces are
required, some sort of multiplexer will be needed or a very well controlled
architecture to make sure the outputs don't walk on each other.


..... NMEA is not bi-directional ....

it uses one set of wire for rx and one for tx
 
P

Peter Bennett

Jan 1, 1970
0
The NMEA0183 interface from my Garmin E-Trex Vista is RS232.

If it is RS-232 levels, it ain't NMEA-0183. (and I'm pretty certain
that it is NMEA-0183)
Depending on the installation, TTL NMEA0183 code may be available before
going to the RS232 converter, though.

A TTL->RS-232 level converter inverts the signal, as well as changing
levels. Since NMEA-0183 is the same "sense" as RS-232, you need an
inverter _and_ an RS-232 converter to convert from NMEA to RS-232.
I have no idea what the "standard" NMEA interface levels are.

Standard NMEA-0183 levels are 0 and +5 volts. RS-232 levels are -5
(or more) and +5 (or more).

Despite the difference in signal levels, most RS-232 serial ports will
handle NMEA levels with no problems.
 
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