On 6/19/07, Peter Todd <pete@petertodd.ca> 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

20x5000 = 100000pF
1uF = 1000nF = 1000000pF
so, how many microfarads will be ?

> 30ohms/1000ft * 50ft = 1.5ohms
>
>
> Now the line should be acting as a low-pass filter, so from wikipedia:
>
> f = 1/(2piRC) = 1/(2 * 3.14 * 1.5 * 0.0001F) = 1061hz
>
>
> So I should be able to transmit roughly 100bytes/second?
>
>
> Yes, I know I'm going to run into lots of other problems... but that can
> be saved for the post I nearly sent to piclist... :)
>
> - --
> http://petertodd.org
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