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Alternator control problem
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Armin Steinhoff
science forum beginner


Joined: 25 Mar 2005
Posts: 8

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Brook Stevens wrote:
Quote:
Dave VanHorn wrote:


Not sure what you mean by "100kHz" but in addition to the rest of the


Sorry, I meant 100k bits per second.

.... and you mean realy "200 devices in a range of 50m" ?

Must some kind of NANO technology :)

Armin


Quote:


suggestions, you CAN run RS232 in a ring topology, where A talks to B and
listens to Z, B talks to C and listens to A, and so on. Messages have a
sender and recipient, and anything that isn't for "me" gets passed along the
chain. You also have a "time to live" that is decremented whenever the
packet is passed, so if it is a 30 device loop, you set that to maybe 32..
When it hits zero, the packet is dropped.

All the devices have to implement the protocol, and deal with
dropped/corrupted packets, but it's a pretty nice way to go, in that at any
point in the loop, only one machine is talking to one machine on a cable, so
you get full bandwidth between all machines, at the expense of a short time
delay to move the packets.


Very interesting! Thanks for the idea.
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Rene Tschaggelar
science forum beginner


Joined: 25 Aug 2005
Posts: 12

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Nico Coesel wrote:
Quote:
"Dave VanHorn" <dvanhorn@dvanhorn.org> wrote:


There is a protocol which deals better with these sort of setups. It's
called TCP/IP.

Seems like a lot of overhead, I guess you could toss out the parts you don't
need.

There are some very space efficient TCP/IP stacks around. I've noticed
its quite hard to put a reliable communication protocol together. It
takes some serious thought on fault detection, re-transmitting lost
packets, time-outs, packet re-alignment, etc. So why try to invent
something new if you can use something that already exists?


Very efficient ?
TCP/IP allows to transmit block of 2^32bits in random
packet order. To as many as 2^32 devices. It adresses
2^16 different ports per device. This is huge overkill
when the packetlength is shorter than 250 bytes, to
less than 255 devices.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
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Jerry Avins
science forum Guru


Joined: 03 May 2005
Posts: 534

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

keith wrote:

Quote:
On Wed, 02 Feb 2005 11:32:32 +0100, Armin Steinhoff wrote:


Brook Stevens wrote:

Dave VanHorn wrote:



Not sure what you mean by "100kHz" but in addition to the rest of the


Sorry, I meant 100k bits per second.

... and you mean realy "200 devices in a range of 50m" ?

Must some kind of NANO technology :)


What's wrong with having 200 devices withing 50 meters?


Let's see ... 200 drops in 50 meters ... on average, the drops are 25
centimeters apart. If the controller is in the middle and the bus goes
out in several directions, the drops may get as far apart as a meter on
average. That's still a pretty tight cluster of machinery/

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
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Jerry Avins
science forum Guru


Joined: 03 May 2005
Posts: 534

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Nico Coesel wrote:
Quote:
Rene Tschaggelar <none@none.net> wrote:


Armin Steinhoff wrote:


Brook Stevens wrote:


Rene Tschaggelar wrote:



I'd go for RS422, a bidirectional bus with one leading in
each direction. Physically identical to the RS485, it doesn't
require you to switch direction at the cost of an additional
line pair. There are input impedances that limit the number
of devices to 32 or 128, depending on the receivers.
So after the number of devices is reached, just add a
repeater.
I'd use 6 wires for the bus. 4 wires for the signal plus
one for GND and +5V. This would enable you to have the local
RS422_to_CMOS plus perhaps isolators powered from the bus.



Thanks Rene. RS-422 seems like a good option for the bus.


RS-422 is not the right choice for a BUS. RS-422 can be used for a
one-to-one (or one to many) communication structure.

Use RS-484 ... or simply CAN and you go with a standard.

What is wrong with implementing a master/slave system onto
a one-to-many bus ? RS422 doesn't require switching the
direction. An RS232-to-RS422 converter takes 3 chips and


RS422 is current loop and therefore only usefull for peer-to-peer
connections. RS485 is a differential interface which may be
implemented as a half duplex bus or a separate transmit and receive
pair for a full duplex peer to-peer connection.

Both RS-422 and -485 are differential voltage. A transmitter enable is
optional with RS-422, but required on RS-485. I wrote of RS-422; that's
how the project started. We switched to RS-485 when we built the prototypes.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
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Keith Williams
science forum beginner


Joined: 19 Apr 2005
Posts: 30

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

On Wed, 02 Feb 2005 21:14:34 -0500, Jerry Avins wrote:

Quote:
keith wrote:

On Wed, 02 Feb 2005 11:32:32 +0100, Armin Steinhoff wrote:


Brook Stevens wrote:

Dave VanHorn wrote:



Not sure what you mean by "100kHz" but in addition to the rest of the


Sorry, I meant 100k bits per second.

... and you mean realy "200 devices in a range of 50m" ?

Must some kind of NANO technology :)


What's wrong with having 200 devices withing 50 meters?


Let's see ... 200 drops in 50 meters ... on average, the drops are 25
centimeters apart. If the controller is in the middle and the bus goes
out in several directions, the drops may get as far apart as a meter on
average. That's still a pretty tight cluster of machinery/

Not nano, though. I wuz thinking more "within" 50m.

--
Keith
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Ajay1
science forum beginner


Joined: 25 Mar 2005
Posts: 3

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: What is Axis Control Reply with quote

Thanks for the support.

I am very much new and so maynot be able to answer questions in my of
the threads so I leave it for experts

And sadly my ISP at work gives me only web access and so I find Google
Groups a good way to get questions answered.
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Armin Steinhoff
science forum beginner


Joined: 25 Mar 2005
Posts: 8

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Fred Bloggs wrote:
Quote:


Armin Steinhoff wrote:

Brook Stevens wrote:

Rene Tschaggelar wrote:


I'd go for RS422, a bidirectional bus with one leading in
each direction. Physically identical to the RS485, it doesn't
require you to switch direction at the cost of an additional
line pair. There are input impedances that limit the number
of devices to 32 or 128, depending on the receivers.
So after the number of devices is reached, just add a
repeater.
I'd use 6 wires for the bus. 4 wires for the signal plus
one for GND and +5V. This would enable you to have the local
RS422_to_CMOS plus perhaps isolators powered from the bus.




Thanks Rene. RS-422 seems like a good option for the bus.



RS-422 is not the right choice for a BUS. RS-422 can be used for a
one-to-one (or one to many) communication structure.

Use RS-484 ... or simply CAN and you go with a standard.

Armin


But, then what
protocol should the devices use to communicate with the PC? The PC
needs to
address one out of 200 devices and tell it to set it's outputs, or to
send
it's inputs.



What's the matter with industrial ethernet, using that cheap 8051 Rabbit
thing with TCP/IP stack- proprietary boards should come in at <$10

Please differenciate between the production costs (<10$ ??) and the end
user price ... or do you are tkinking about GPLed hardware? :)

Armin

in
Quote:
quantity- just tell the nodes to shut up unless spoken to- no
crashes/clashes or whatever they're called- cheap UTP cabling.
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Armin Steinhoff
science forum beginner


Joined: 25 Mar 2005
Posts: 8

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Rene Tschaggelar wrote:
Quote:
Armin Steinhoff wrote:

Brook Stevens wrote:

Rene Tschaggelar wrote:


I'd go for RS422, a bidirectional bus with one leading in
each direction. Physically identical to the RS485, it doesn't
require you to switch direction at the cost of an additional
line pair. There are input impedances that limit the number
of devices to 32 or 128, depending on the receivers.
So after the number of devices is reached, just add a
repeater.
I'd use 6 wires for the bus. 4 wires for the signal plus
one for GND and +5V. This would enable you to have the local
RS422_to_CMOS plus perhaps isolators powered from the bus.




Thanks Rene. RS-422 seems like a good option for the bus.



RS-422 is not the right choice for a BUS. RS-422 can be used for a
one-to-one (or one to many) communication structure.

Use RS-484 ... or simply CAN and you go with a standard.


What is wrong with implementing a master/slave system onto
a one-to-many bus ?

If a strict master / slave relation ship is OK ... why not.

Quote:
RS422 doesn't require switching the
direction. An RS232-to-RS422 converter takes 3 chips and
fits onto a square inch. I'm not familiar with RS484, a
search turned up only fluff.

Oh ... I just hit the wrong key. RS485 is the correct one.

Quote:
CAN is a fast bus but is limited to 6 byte messages or so.

8 bytes of data ... there is room for are 32 input and 32 output signals
and this is more than requested.

Quote:
The last time I looked at it, there was no provision for
longer packets.

Longer messages are handled by CANopen ...

Quote:
The command set has to be designed to fit the application
in question. I doubt the car industry has a fixed commandset
and all CAN subsystems are compatible across the maufacturers.
Just guessing...

No ... there is a real confusing set of incompatible layer 7 protocols
used by the car industry.

Quote:

Rene
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Mike Amling
science forum Guru


Joined: 05 May 2005
Posts: 525

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Armin Steinhoff wrote:
Quote:
Fred Bloggs wrote:



Armin Steinhoff wrote:

Brook Stevens wrote:

Rene Tschaggelar wrote:


I'd go for RS422, a bidirectional bus with one leading in
each direction. Physically identical to the RS485, it doesn't
require you to switch direction at the cost of an additional
line pair. There are input impedances that limit the number
of devices to 32 or 128, depending on the receivers.
So after the number of devices is reached, just add a
repeater.
I'd use 6 wires for the bus. 4 wires for the signal plus
one for GND and +5V. This would enable you to have the local
RS422_to_CMOS plus perhaps isolators powered from the bus.





Thanks Rene. RS-422 seems like a good option for the bus.




RS-422 is not the right choice for a BUS. RS-422 can be used for a
one-to-one (or one to many) communication structure.

Use RS-484 ... or simply CAN and you go with a standard.

Armin


But, then what
protocol should the devices use to communicate with the PC? The PC
needs to
address one out of 200 devices and tell it to set it's outputs, or
to send
it's inputs.



What's the matter with industrial ethernet, using that cheap 8051
Rabbit thing with TCP/IP stack- proprietary boards should come in at <$10


Please differenciate between the production costs (<10$ ??) and the end
user price ... or do you are tkinking about GPLed hardware? :)

Armin


It looks like the "Rabbit" line is overpriced at $31ea qty 100 just for
the controller. Forget them. Microchip has flash PICs and freeware for
developing TCP/IP applications, and they have several app notes on
developing an SNMP which should work well for this network where
everything centers around a 16-bit status and single bit control
commands.
http://www.microchip.com/stellent/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2008
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Nico Coesel
science forum beginner


Joined: 25 Mar 2005
Posts: 4

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Rene Tschaggelar <none@none.net> wrote:

Quote:
Brook Stevens wrote:


You're right, that was unclear. I meant 100Kbps. I realize the protocol will
have some overhead, and that's fine. And I could maybe get by with a lot
less. For example, I have to feed a powder from a loss-in-weight feeder. The
PC has to control the feeder motor and monitor the weight. I have different
options for controlling the motor. If I use stepper motors and try to
control every step from the PC, I need more speed. If I just tell it
start/stop, then I don't need nearly as much speed.



Ooohhhh, nooooooo.
Never attempt to control a process with a PC. A PC is not
reliable enough. Nor can a timing be guaranteed.
A floting point error in some unimportant display routine
can stop the application.

If you hired the wrong programmer... If you separate the control
processes and the user interface, there is not much which can go
wrong. If you can tolerate 100ms response time, a professional PC
running Windows will do fine for controlling processes.

Quote:
You always have to consider the PC stops working. The
motors running keep running. The heaters keep

This goes any control system. You'll need electromechanical fail safes
for any critical system.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
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Nico Coesel
science forum beginner


Joined: 25 Mar 2005
Posts: 4

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Rene Tschaggelar <none@none.net> wrote:

Quote:
Nico Coesel wrote:


If you use a standard ethernet chip, it will do most of it for you at
high speed using standard cabling, standard hubs / switches, etc.
Besides, the more advanced IP stacks will collect a number of packets
(nagle algorithm) for a given target and send them as one packet to
reduce overhead. If you send a lot of short messages to a target from
-let's say a PC- in a short period, the target will receive 1 or more
long packets.

Yes, the ethernet chip does up to the IP level. Meaning
1500 something bytes, no ports, no retransmit, no reassembly.
It may depend from which platform you look, from an 8bit
micro TCP/IP is a heavy burden. I'd possibly prefer UDP
if it had to be. The random transmissions have to be
controlled somehow to reduce collisions. But a master-
slave setup should do that nicely.

No, not UDP. You'll need something which is acknowledged. This gives
you reliability and keeps the master waiting for the target to finish
and acknowlegde the operation. This prevents overflowing the target's
buffers.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
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Brian
science forum beginner


Joined: 16 May 2005
Posts: 45

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Quote:
It looks like the "Rabbit" line is overpriced at $31ea qty 100 just
for
the controller. Forget them. Microchip has flash PICs and freeware
for
developing TCP/IP applications, and they have several app notes on
developing an SNMP which should work well for this network where
everything centers around a 16-bit status and single bit control
commands.

I may be biased working for Rabbit, but I say don't forget it.

A PIC doesn't have enough flash or RAM on chip for a robust
implementation of a TCP/IP stack and SNMP to boot, so the external
flash and RAM already on the Rabbit Core Modules will be needed for the
PIC too.

By the time he puts together the HW, tools, stack, and SNMP and starts
writing his application for a PIC-based product, he could have the
Rabbit version on the shelf. SNMP is already implemented on top of a
mature, robust, royalty-free TCP/IP stack. Support for the HW,
development tools, stack and RTOS (if one is used) all come from the
same place.

If he wants to move into higher volume he can incorporate the core
module design and just buy Rabbit chips and use the same SW. If he
wants a web server and browser interface for the app, a rapid
application development system for web interfaces will save weeks of
complex CGI programming:
http://www.rabbitsemiconductor.com/products/dc/DC9/modules.shtml#RabbitWeb
If he wants to add higher security to it, SSL/HTTPS is also implemented
and takes advantage of special Rabbit instructions to make it fast,
which it won't be on the PIC.

A full version of the development tools with the TCP/IP stack and over
700 sample programs and applications come with the inexpensive
development kits:

http://www.rabbitsemiconductor.com/products/rcm3700/
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Rene Tschaggelar
science forum beginner


Joined: 25 Aug 2005
Posts: 12

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Jerry Avins wrote:

Quote:
keith wrote:

What's wrong with having 200 devices withing 50 meters?

Let's see ... 200 drops in 50 meters ... on average, the drops are 25
centimeters apart. If the controller is in the middle and the bus goes
out in several directions, the drops may get as far apart as a meter on
average. That's still a pretty tight cluster of machinery/

Lets see. 50m radius makes almost 10000m^2. You'd fit
100 devices in there with 10m distance each.

Rene
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Rene Tschaggelar
science forum beginner


Joined: 25 Aug 2005
Posts: 12

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Nico Coesel wrote:

Quote:
Rene Tschaggelar <none@none.net> wrote:


Nico Coesel wrote:


If you use a standard ethernet chip, it will do most of it for you at
high speed using standard cabling, standard hubs / switches, etc.
Besides, the more advanced IP stacks will collect a number of packets
(nagle algorithm) for a given target and send them as one packet to
reduce overhead. If you send a lot of short messages to a target from
-let's say a PC- in a short period, the target will receive 1 or more
long packets.

Yes, the ethernet chip does up to the IP level. Meaning
1500 something bytes, no ports, no retransmit, no reassembly.
It may depend from which platform you look, from an 8bit
micro TCP/IP is a heavy burden. I'd possibly prefer UDP
if it had to be. The random transmissions have to be
controlled somehow to reduce collisions. But a master-
slave setup should do that nicely.


No, not UDP. You'll need something which is acknowledged. This gives
you reliability and keeps the master waiting for the target to finish
and acknowlegde the operation. This prevents overflowing the target's
buffers.


Why not acknowledge on the application level ?
Just an Ack is boring. A real reply would lower
the load of the bus.

Rene
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Jerry Avins
science forum Guru


Joined: 03 May 2005
Posts: 534

PostPosted: Fri Mar 25, 2005 3:21 am    Post subject: Re: CHEAP Serial bus, control 200 devices, 50 meters Reply with quote

Rene Tschaggelar wrote:

Quote:
Jerry Avins wrote:

keith wrote:


What's wrong with having 200 devices withing 50 meters?

Let's see ... 200 drops in 50 meters ... on average, the drops are 25
centimeters apart. If the controller is in the middle and the bus goes
out in several directions, the drops may get as far apart as a meter on
average. That's still a pretty tight cluster of machinery/


Lets see. 50m radius makes almost 10000m^2. You'd fit
100 devices in there with 10m distance each.

Rene

But how long will the signal wires be?

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
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