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

Hello Stef,

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

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

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.

Hello Stef,

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

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?

Yes, IR is on the list of candidates.

Hello Stef,

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

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

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

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.

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

Regards, Joerg