Re: Re: Sensors / Switches / etc

["Dan" <dtoma@xxxxxxx>]

> A single bus is a Bad Thing imo. Do you remember the days of thin
> ethernet cabling? A single, daisy chained bus, is a nightmare from
> the point of view of discovering where a break occurs in the network.
Break is not an issue... the devices are all connected to the same pin.
A defective device can be a little bit difficult to debug if it force the
output on the bus...

> Depending on the network design, it may also require that all devices
> are active for the network to function properly.
It is enough to keep the output in a high impedance state.

> Then there is also
> the issue that if you cannot add or remove a device from the network
> with (albeit temporary) interruption to the network.
Not really true..as you must disconnect a single wire, the network is not
interrupted.


> OK, at one level you could argue that ethernet is "just a very
fast
> serial network". But remember the motives for using a serial
network -
>  it's cheap. High speed networks (say >19k2 baud) need fast
> processors, and cost starts to climb.
For Home Automation purpose a 9600bps serial bus is enough.. Do not
forget.... X10 work at 100bps...:-))

> At the lower end of the scale,
> a 9k6 or 1200 baud serial network is severely limited in terms of the
> number of symbols you can push down the wire in a second.
You do not need to pass a lot of information... just something like a
address/status/command and maybe a heartbeat.


> If you have
> a large number of devices competing for the network infrastructure,
> the time taken to transmit a command to/from a device is (a) going to
> vary significantly depending on current network activity -->

> perceived unpredictability from end users perspective and (b) may
> take a significant amount of time (>750ms say).

This can be an issue if you have a lot of "high traffic devices",
but
usually, except infrared. there is not the case..

BR,
Dan