Re: [ha] My proposed system
Mon, 26 Oct 1998 16:18:56 GMT

"Neil Wrightson" <> wrote:
> Dallas 1 wire devices such as Inputs, Outputs Temperature sensors, ID
> Buttons etc.
Yes, these are interesting products. I would like to have a play with
some of them. But I think the advantages of the 1-wire bus are overplayed
by Dallas. At best it's actually 2-wire (signal and ground) and you are
limited in what devices you can connect and how you can address them in
this mode. To do anything sensible, it really needs 3 wires to provide
separate power. But even then, the capacitance requirements are hard to
meet over any real installation. I think it ideal as a local peripheral
connection mechanism, but I wouldn't run it any distance.

In the home-brew system, maybe we could have a PIC or something programmed
as a HB-to-1-wire interface so a cluster of 1-wire devices could be
attached to the system.

> The 1 Wire devices are good for small I/O point distributed around the
> building, pool, greenhouse etc...
What I/O devices are in this range? I only know about the temperature,
clock and memory modules.

> ...but are not good for faster data transfers ... For this I plan on
> using a 4 wire system 0V, 12V & RS485 (remaining two wires).
RS485 is a cheap and robust scheme capable of some impressive data rates.
I am running some radio modems at the end of a 50ft length of phone cable
running through a noisy building and they are reliably doing 1Mbit/sec.
RS485 would be a good bus to use in the Home Brew project.

> ... I like the idea of dedicated controllers ie black box on the wall,
> overseeing control of each respective area. not to many eggs in the one
> basket. Unfortunately this route is not available to the large majority
> of basement engineers due to the high cost of dedicated controllers,
> specialised eprom programmers etc.
The way I see this taking shape in my mind, individual switching units
will be bright enough to respond directly to the appropriate stimulus.
e.g. in the simplest case of a light switch, the lamp unit and corresponding
switch(es) will be programmed somehow to know that they are associated.
Each switch will just send out its new state when it is operated
and the lamp will respond directly. There is no need for any additional
intelligence here. I imagine that this can easily be accomplished by
most of the microcontrollers we have mentioned so far (maybe the PIC
is a bit of a stretch).

For more complex situations, the direct association would be broken by
having some more intelligent controller in between, so the switch reports
to the controller and the controller gives orders to the lamp.


R.M.O'Leary <> +44 7010 7070 44, PO Box 20, Swansea SA2 8YB, UK