wouter van ooijen wrote:

>> My speed requierments are very low, 500bytes/sec for the whole bus would
>> be fine for this application. I'll only need to update maybe 100 nodes
>> once per second with say a 1 byte payload, 4 byte address.
> 
> some remarks: 
> 
> If your communication is downstreams only a current-loop might be a nice
> idea, although at 100 nodes the source voltage might be a bit high. 

Main consideration here is probably whether the public has access to the
wires. The nice thing is that you don't have to deal with large currents.

> There is no law that the lower voltage on the bus should be 0V: I can
> imagine a but with for instance signalling levels 9V and 12V. 

Works for downstream only. You have some power to get rid of at the sender,
though.

> Alternatively signalling can be in HF, which can easily be added/removed
> from the power line. 

Yes, RF or even audio (DTMF or modem type modulation).

> 100 nodes might be too large for some setups, maybe split in separate
> strings, or add repeaters.

Good ideas. Add the possibility to do the communication in short intervals
where you don't have power on the bus. 

Gerhard

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