Re: Wireless/powerline comms, short distance, 100 nodes

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Each rail (there are 2) is about 2 metres long, the ends are close together
and from there, there is 2-3 metres of cable to the control cabinet. If
needed, the powerline interface could be mounted close to the rails, but
the preferred location would be in the cabinet.

Required datarate is 2400 - 9600 bps. One of the operations is a sync
cycle that is currently handled by a separate hardwired signal to all
modules. The response here is in the us range and this is obviously not
possible through the powerline comms. I can compensate for a longer time
as long as the delay is fixed. I might be able to relief the jitter
requirement by changing/elaborating the sync cycle if needed.

Most other commands require a response within 10 - 100ms. All commands
are only a few bytes long (2 - 5).


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Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

Women are just like men, only different.

Re: Wireless/powerline comms, short distance, 100 nodes
Hello Stef,

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2400-9600 bps per node? I think that won't fly via powerline, at least
not in a noisy industrial environment.

I would consider an ISM band transmitter for the (hopefully few) signals
that require microsecond response times.

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With that much allowed latency you could consider WLAN for these
channels. It provides lots of bandwidth for your data rates. Then there
is Bluetooth, spread spectrum such as used by upscale cordless phones
etc. Best is to stick with something that has already undergone agency
certification for other uses. Otherwise this project could become quite
expensive.

Regards, Joerg

http://www.analogconsultants.com

Re: Wireless/powerline comms, short distance, 100 nodes
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No, not per node, in total. Most commands are broadcast, like: "All nodes
perform function A". Then there is some configuration and status checking
that needs to be done per node, but this can be relatively slow and uses
a request/reply protocol.

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Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

I have a very small mind and must live with it.
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Re: Wireless/powerline comms, short distance, 100 nodes
Hello Stef,

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Then it could be done via the power line but in a noisy environment I
still would not do that. You could send all this via a simple RF link.
For example, assume you had a cordless phone on the carriage and another
one on the floor. Via a modem you could now send all that data. This may
be a bit over-simplified and whether or not a spread spectrum phone
would work would have to be checked. You could use one of the Texas
Instruments or Nordic transceivers.

Also, think about IR for simplicity. If pointed upwards to a diffuse
reflector it could work. It's a matter of power and efficiency. Once in
a hotel I could not believe it when the remote for the TV would still
work when held at the ceiling instead of the TV. So I went into the
bathroom and pointed it at the hallway wall. The IR had to bounce at
least three times to get to the TV. It still worked.

Regards, Joerg

http://www.analogconsultants.com

Re: Wireless/powerline comms, short distance, 100 nodes
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It is a separate 24VDC powerline, but it has up to 100 DC motors on
it and there are sliding contacts. So it will be noisy.

Would you advise RF in a noisy environment? That does not seem logical
to me. Can these phone tranceivers handle up to 100 simultanious
connections or would I need to switch on one at the time? If one at
the time, how fast can I expect to scan all nodes?

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Yes, IR is on the list of candidates.

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Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

What foods these morsels be!

Re: Wireless/powerline comms, short distance, 100 nodes
Hello Stef,

Was on a biz trip, this one w/o NG access.

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That is noisy but you can slide ferrite beads and stuff over the supply
leads.

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Above a GHz you won't see much of the DC motor noise anymore.
Simultaneous xmit/rec isn't feasible since that would usually require
100 modules. Polling could be done in milliseconds per node. You'd have
to talk with the folks from Nordic or another manufacturer to find the
most cost efficient modules for your requirements.

It's the same with all other protocols, even powerline. You can only
poll one at a time or you would need 100 carriers and receivers.
Theoretically you could send out on various frequencies and have a DSP
figure out all those carriers. But at a hundred that would be a huge DSP
job.

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And it may be the most cost efficient candidate if you can make it work.

Regards, Joerg

http://www.analogconsultants.com

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