LONWorks vs. Ethernet

> 
> I think they avoid reflection problems by riding the data on a sine
> wave carrier of 5-40MHz, depending on which transceivers you use and
> how they are configured.  I'm not sure exactly what sort of modulation
> they use, but the effective communication rate is 78kbps.  I'm not an
> electrical engineer, but I think sine waves are pretty immune to
> reflections, right?  This stuff is getting into black magic territory
> for me -- I don't want to have to understand wave propagation, I just
> want a reliable network.
>

Sine waves reflect too. I was intrigued so I looked at their website
and it looks to me that maybe the bandwidth of the signalling method is
limited to avoid reflections. Although they do mention termination:

http://www.echelon.com/products/oem/transceivers/twisted_pair/aboutfreetop.htm

and also mention that you can do 2000M with terminated bus topology:

http://www.echelon.com/products/oem/transceivers/lpt/default.htm

> On the other hand, I could probably live with a data rate of around
> 28.8kbps.  At that sort of rate, if I have a slew-rate-limited RS-485
> transceiver, I can probably get away with unterminated, mixed-topology
> wiring, right?

It depends on how slew-rate limited the RS485 drivers are, and how long
the wiring is. I wonder what the slowest available RS485 driver is? This
method however does look quite primitive compared to the Lonworks stuff -
it looks like a nice solution. I haven't used it, but did come into
contact with it on a project (someone else was doing the lonworks), and I
got the feeling that Nueron chips themselves where pretty awful, with the
Nueron C. But the networking stuff looks good.

Regards,

Paul.

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Hello Randall,

Why not try to find out which LonWorks modules already exist that can
do your job. That way you don't have to go to deep into LonWorks.

I know that there are several LonWorks manufacturers that do have
(multi-channel) analogue input modules.

Also, I would suggest that you ask your questions in the LonWorks
Conference on the Echelon site. A lot of Lon folk is using that as the
LonWorks newsgroup.

Kind regards,

Maikel

Randall Nortman wrote:
> 
... snip ...
> 
> I think they avoid reflection problems by riding the data on a sine
> wave carrier of 5-40MHz, depending on which transceivers you use
> and how they are configured.  I'm not sure exactly what sort of
> modulation they use, but the effective communication rate is
> 78kbps.  I'm not an electrical engineer, but I think sine waves are
> pretty immune to reflections, right?  This stuff is getting into
> black magic territory for me -- I don't want to have to understand
> wave propagation, I just want a reliable network.

Nothing is immune to reflections, because all signal propagation is
over lines.  The adage "everything is a line" applies.  The effects
may become small in comparison to the signal under certain
conditions.  Line length is effectively how you achieve resonant
antennas.  Line termination effectively extends the line
indefinitely, so that the signal never reaches the end, and thus
never reflects.  Exact termination is inherently impossible, so
some small fraction of signal is always reflected, but may well be
undetectably small.

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The FTT tranceivers from Echelon are very easy to use. Generaly you can
get away
without any network termination for smaller networks, however, for
complete
robust communications you will need a termination, but only one, at
some piont
on the network. This can be at any convenient location.

The FTT transceivers have a small DSP onboard to resolve the digital
signals.
This is why the network can have a free topology.

Lonworks and the word "cheap" have never gone together. However, you
pay for
what you get. Lonworks contains it's own protocol that works. Other
systems
such as CAN do not have a protocol, they are simply a transport
mechanism.
You would have to incest time and money into developing your own
protocol
or adopt a standard such as CANopen or DeviceNet.

For quick development you can buy FTT modules from Echelon. You will
need
some sort of development environment.

Alternatively, I think there is a Lonworks protocol stack chip that is
fairly
affordable that can be connected to a processor via SPI. this would
then allow
you to use your favouite processor and evelopment environment. No need
to adapt
to Neuron C.

Hope that helps.

Randall Nortman wrote:
> I need to build some little devices to install throughout a small
> building, each of which will take readings from 2-6 analog sensors
> (10-bit resolution, 1 sample/sec is plenty).  Some of the pods will
> also need to drive a few low-power relays.  I want the networking to
> be all digital, with the sensor readings going back to a headless
> Linux PC, which also sends signals back to open and close the relays.
> The remote devices should be very cheap, and the networking should be
> reliable and flexible in terms of topologies.  Delivering DC power
and
> communications over the same cable would be ideal.
>
> I know squat about Echelon/LONWorks, beyond the little I've been able
> to figure out from reading their website, which buries the technical
> stuff I need to know in mountains of marketing propaganda.  But
still,
> it seems like it could do the job.  They have a version that can do
> the communications over the same two wires that provide DC power,
> which is convenient.  What I don't know is how I would interface ADC
> chips and relay drivers to the Neuron chip, how I program the thing,
> and how much the chips, transceivers, and external components cost
> (ballpark, quantity 100 or so).  And if the development tools are
> commercial (and I hate commercial development environments), how much
> do they cost, and do they run on Linux?  Also, is the thing really
> reliable and tolerant of less-than-perfect wiring?
>
> The alternative is to bring out the big guns and run an embedded
Linux
> on an SOC/SBC and just use Ethernet (preferrably with Power over
> Ethernet) and TCP/IP.  This is appealing because I know Linux very
> well, and I can develop for it using free tools.  I suspect the
> downside is the cost.  I think it's worth paying a little more for
the
> convenience of using something I know, and which is widely supported
> in all sorts of industries.  But without knowing how cheap LONWorks
> can be, I don't know how much of a premium I'm paying for the
> convenience of Linux.
>
> I should also say that I've considered using an 8-bit microcontroller
> (eg Atmel AVR) and RS-485, but then I have to write and debug an RTOS
> and network protocol, plus my experience with RS-485 has been that
> it's far too sensitive to wiring imperfections, and the network
> topology is too limited.
>
> So, any thoughts?  Can anybody with LONWorks experience give me some
> advice on whether that's a good option, and how much cost I should
> expect to save vs. Ethernet?  Any suggestions of very cheap SOCs/SBCs
> if I want to go the Linux route?

If you want to take advantage of an existing electrical network,
you could look for homeplug devices
for instance http://www.maxim-ic.com/powerline.cfm

On 28 Apr 2005 06:54:52 -0700, "Rob" <mr_horton@yahoo.com> wrote:


>Alternatively, I think there is a Lonworks protocol stack chip that is
>fairly
>affordable that can be connected to a processor via SPI. this would
>then allow
>you to use your favouite processor and evelopment environment.

This is called the lonworks "short-stack" API.  I recall that it can
be accessed by SPI or UART versions.  However, it is not a complete
interface, as network management operations are not supported.
Therefore it is not possible to commission a lonworks network using
the shortstack API.


regards,
Johnny.