At 10:14 PM 6/19/2007, you wrote:
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>
>I'm writing a feasibility report for a project that would involve
>placing hundreds, or even thousands, of little nodes consisting of a
>really low end PIC, 12f or even 10f, and an PWM'd LED, in trees
>outdoors. The project is fairly cost sensitive, given the scale, so I
>was thinking of some sort of software one-wire bus implemented on cheap
>CAT3. After spending a few hours thinking everything else through, er, I
>mean as a responsible first step, I thought I'd try to figure out the
>characteristics of my transmission line:
>
>Nodes: 100
>
>Distance needed: ~50ft/node to master, w/ star topology, 5000ft total
>
>CAT3 is 20pf/ft, 30ohms/1000ft
>
>20pf/ft * 5000ft = 100uF

1 pF is 10^-12 F. So you actually are looking at 100nF, not uF.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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