Re: LONWorks vs. Ethernet

On Tue, 26 Apr 2005 20:35:11 GMT, Randall Nortman
<usenet8189@xxxxxxxxxxxxxxx> 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?
>
>Thanks very much,

I can't comment much about embedded linux since there are so many
different boards from different vendors with different levels of
support. Generally it looks like an expesive option. The other issue
is that if you want to service the network in the future, the SBCs may
go obsolete, and you probably can't use the same application image. I
don't know if service support is an issue for you.

I have a bit of experience with Lonworks, and it would be a good
solution if you want very good comms reliability for a reasonable cost
per device. But you should only consider starting it if you are very
serious about getting into the buidling controls industry as a volume
manufacturer. One issue is that Lonworks is not really an open
protocol. The software development tools are aimed at the LSN network
plugin environment which means using you must create device profiles
that allow you device to be installed using the standard network
management tools. These tools are proprietary to Echelon corporation,
and you need to pay a license fee every time you install a device
using their tools. Apart from this there is quite a steep learning
curve to create LNS based applications, and you will need to check the
cost of the development tools.

The AVR is a far superior device to the Neuron chip as far performance
is concerned. The neuron chip scheduler is just a joke. It is
horribly slow and non-deterministic being a co-operative scheduler
without any way to service real time tasks. The main problem is that
the Neuron chip does not support interrupts so this makes it
impossible to write applications have reasonable IO latancies.

Personally, I would look at the AVR with RS-485 as the first option.

regards,
Johnny.











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