RE: Re: Your Opinions please

["Dave McLaughlin" <dave@xxxxxxx>]

Hi Mark,
-----Original Message-----
From: mark_harrison_uk2 [mailto:mph@xxxxxxx]
Sent: 01 September 2003 22:41
To: ukha_d@xxxxxxx
Subject: [ukha_d] Re: Your Opinions please


You are joking, aren't you? The Microsoft Home Control Protocol has a
message size of about 22k (ie - 1500 times the size) to accomplish
the same thing.

> Nope, but I would expect Microsoft to use Bloatware if at all
possible.

Of course, if you're writing a protocol ONLY to do something very
simple like turn lights on and off, then you can write it small. You
can switch on a light in a couple of bytes...

> I guess my own protocol is designed for switching outputs on or off
and
to read back status.
> xAP as I understand it can do more.

> My own system can have multiple devices on the same bus. At present I
have my weather
> station sending out information constantly and the garage doors status
is also on the bus.
> I can also run the control devices on this same bus and each device on
the network can
> decide to use the information or ignore or discard it. I can add a
transmitting or receiving
> device to the bus without the need to reprogramme any of the existing
devices, unless that
> is that they need to decode the new devices information.

If you're writing a general protocol like xAP, then you can't. Hence
the need for translation onto the HA equivalent of the "last
mile".

The question is - which would you prefer? A protocol that's common
across large classes of devices, and multiple computer platforms, or
yet another proprietary protocol for yet another proprietary bus.

The largest domestic xAP installation runs primarily on an RS485 bus,
has over 120 devices on it, and still runs very fast in the field.

> CAN bus is not proprietary but a freely available bus that is now used
in anything from
> cars, aircraft, marine and even medical.
>
> My own gripe with RS485, having used it loads of times in the past for
subsea control
> systems is the need for a master to control the flow of messages on
the
bus.
> When we changed to CAN bus because of the multimaster capability and
reliability
> of the protocol.
>
> xAP in it's own nature, until you guys came up with the solution and
made it freely
> available, was a proprietary protocol on an established bus. It can
easily be
> used on a proprietary bus if the designer so wished. Radio for
instance=
.
>
> As a matter of interest, who runs the 120 devices on xAP. I used to
hav=
e
30+ devices
> running the old Quantech System and this was fast but definitely
proprietary.

The difference in price between a PIC with 2k and 64k is, AIUI, a
matter of pennies not pounds. With X-10 modules at =A315-20 a pop, the
difference is a few percent of the cost. The difference in capability
is huge. I would say that the current price-point of X-10 modules HAS
to be a realistic target...

> Yeh, you are right about the price difference. I use the AVR and the
difference from a 8K
> to a 128K device is only about double the cost and at about =A36.00
for
the 8K device this is
> pennies (1 off costs)

Over the last 10 years, the price of (disk, memory, etc.) has fallen
by a factor of about 2,000. Even if it only falls by a factor of 500
over the next 10 years, that's still enough to make a couple of
hundred bytes fine for fractions of pennies.

Now, I will concede that there IS still one place where ultra-low
bandwidth / processing power is king, and that's in mains-modulated
data...

... but I would predict that market to have been completely overtaken
by wireless in the next 5 years (unless one of the much-vaunted high-
bandwidth mains projects finally goes mass-market.)

Mark

> I would to see the wireless system come about but I do see what Ian
Davidson was referring
> to in his post earlier this evening, in that the signal strength issue
may be a problem in
> brass faced wall mounted designs. This becomes more apparent in metal
clad flush boxes
> that most houses are wired with.
> As you say, time will tell.

Regards
Dave...
PS.. I will be looking at the xAP stuff now with an interest in using it
alongside my existing
control systems. I do like the idea that I can use it to send text for
display on LCD's etc.

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