Wired Sensor Network

.. might work for you, but it's not exactly what you are asking for (only a single master).

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com

I think you hit the nail square on the head. This system occured to me just as I hit the "send" button, and I've been researching it in the past few minutes. Sure looks promising. Thanks for your help!

CANbus. Peer to peer (multiple master) with built-in collision detection and retransmission. Typical microcomputer CAN peripherals have acceptance filters so that listeners are not bothered by messages they don't care about. Decent rates, 1 Mbps for short (40 meter) runs, 125 Kbps and 250 Kbps often seen for longer runs.

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Rich Webb     Norfolk, VA

A simpler system would be with an RS-485 line driver.

Google for RS-485 and lots of circuits and software will be made available.

Here's a start:

hamilton

On a sunny day (Tue, 04 Jan 2011 07:02:25 -0700) it happened hamilton wrote in :

Or ethernet, with power over ethernet. Maybe a bit overkill here, but it is sort of a standard, cables and connectors are too.

The HART protocol

might be an overkill for your application, but runs on standard 4-20 mA current loops.

Why not simply use a master/slave protocol and address slaves individually and only the addressed slave sends the data.

If you do your own protocol, one pair should be enough. Put all stations in series and power the loop with a sufficient voltage (24-60 V). Each device needs a rectifier and storage capacitor in the power supply to ride through the time when the "Space (0)" bit is sent. Use two stop bits so each asynchronous character has at least two bits in the Mark ("1") state to charge the storage capacitor even if start bit+8 data bits with "0" and even parity is sent.

Not necessarily simpler if there are multiple, asynchronous transmitters. A 485 bus with that requirement pushes back onto the implementer the need to come up with a method of handling collisions.

CAN peripherals can be a pain in the tuckus to set up but once that's done you get "free" collision detection & retransmission, message prioritization, and a built-in hardware CRC with every packet.

As Jan mentions, Ethernet -- particularly UDP/IP -- is another possibility.

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Rich Webb     Norfolk, VA

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All are possible, but depends on distance. What are the spacings and distances of the sensors?

Don't know yet. Sensors will likely be "clustered" in various areas, then report back to a central monitor/master. An example (not what I'm actually doing), would be a fire alarm system. You have sensors in rooms on different floors. All report back to a master alarm panel. Each floor could be considered a "cluster" where the sensors are spaced relatively close to each other. The master station may be far away from the individual clusters.

Thanks to everyone who responded. You've given me a lot to research and think about. There look to be several ways to go with this. I need to carefully evaluate each method and see which will be the best for the situation, including which is the easiest to implement and cost is a factor too.

For house size, no reason not to wire with cat-6 (8 wires), whether you run ethernet or not. You can always use 3 of them for RS232 and 5 for token/polling/arbitration/etc.

For my new house, there will be double cat-6 to every room, including bathroom. I don't like wireless in the house any way.

Is this homework? Just work out a software handshaking protocol, unless you need like a billion BPS or something.

You could use telephone wire if you've got a slow enough data rate, and either async (like modems used to use) or add some wires and clock the data in/out like that two-wire protocol, which I forget what it's called.

Good Luck! Rich

Nope, not homework, research. "If this was homework, we'd know the answer" Not wiring up my house either. Something equivalent to a block of apartments. Not looking to re-invent the wheel. I want to work smart when I can, and only work hard when I have to. Looks like there are plenty of commercial, simple solutions available. Thanks again to all who answered..

Still the same: Async. Transfer Mode. Just faster.

d.

For longer distance, you might want to look into fibers. I know you don't need the speed (Gs), but better isolation. It would cost around $1 per meter, plus equipments. Right now, I am looking into some RS232/GBIC converter modules.