Interconnecting classic computers

[CRC]

On  Tue, 06 May 2008 07:53:52 -0500 Jules Richardson wrote:

>> Jules Richardson noted:
>>
>>> Hmm, I've got a deep mistrust of any 'data over the mains'  
>>> technology, but
>>> might that be an option here? I assume *most* of your systems are  
>>> physically
>>> plugged into the mains anyway, so it'd meet the ideal requirement  
>>> for no extra
>>> cabling. Data rates presumably not lightning fast, of course...
>>
>> I don't think security is of concern here unless you are extremely
>> paranoid or are transferring prohibited material [...].
>
> Ahh, no - on that note I meant 'mistrust' as in reliability. Running  
> data over
> power lines always seems like the sort of thing that'd work in the  
> lab, but be
> a little unreliable out in the real world with all sorts of 'noisy'  
> devices
> plugged into the system.
> [...]

Actually the X10 home automation system is quite reliable as its  
longevity attests. Currently, broadband over power is being deployed  
in a number of test cities in the US (much to the chagrin of Hams - it  
tends to raise the noise floor in ham bands excessively) and the usual  
suspects are peddling home networking over the mains (e.g. <http://www.dlink.com/products/?sec=1&pid=561d 
 >).

To get around the noise issue, these systems use burst transmission at  
the zero voltage crossing point when line noise is statistically the  
least.

As I mentioned previously, a number of folks make transceivers for  
this purpose. Echelon <www.echelon.com> has made their entire business  
based on this technology used mainly in commercial applications. <http://www.powerlinenetworking.co.uk/component/option,com_frontpage/Itemid,1/ 
 > is a UK firm pushing the technology locally.

IC transceivers are available from ST, Maxim, and SiConnect. The  
addition of a small micro to do the RS232, support logic, and power  
supply should make a useable system meeting Tony's requirements.

	CRC