home automation question

[geoffrey mendelson]

On Apr 21, 2010, at 3:55 PM, Itay Donenhirsch wrote:

> hi
> if you already mentioned avr and would like to build things yourself  
> then you can definitively build it yourself, see
> tuxgraphics.org/electronics/200606/article06061.shtml (you'll need  
> an enc28j60 as well).
>
> you can buy avrs through ebay/digikey/mouser or in israel either  
> arihav or some stores in shdreot bnei zion, ta.
>
> a question though - why ethernet of all things? why not lay an  
> rs-232 cable (avrs got internal uart for that) + max232 for the  
> voltages and be done with it?


Real RS-232 (+- 12v) fades out at about 25 feet. The incorrect  
implementation (+5/0v) fades out after 2-3 meters.

10/100 BaseT is supposed to be good for 100 meters, however many of  
the cheap chipsets are not reliable at that distance. One hub I once  
saw advertised (and I have since forgotten which one) proudly stated  
that it had 1 port that would work to 100 meters, unlike most that  
would not, nor the other ports on it.

Geoff.

-- 
geoffrey mendelson N3OWJ/4X1GM
Jerusalem Israel geoffreymendelson at gmail.com
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge  
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