[TriEmbed] I2C range extension

[Pete Soper]

On 10/02/2015 01:03 PM, John Vaughters via TriEmbed wrote:
> From a product specification perspective, PoE is going to take into 
> account the full 100 meters and then you could factor in about a 10 
> times safety ratio. You could engineer the amps based on type of wire 
> and the current limits relative to length, but realize that the 
> insulation is pretty thin as well. Based on the information from this 
> email string, I suspect you could easily use PoE in a custom 
> engineered standard and have plenty of power to spare, while 
> maintaining safety. But that statement is based on much shorter cable 
> runs than 100 meters, which I feel confident most of us will not use. 
> If you DO use the full 100 meters, I would definitely not violate the 
> specification. CAT 5 was never designed for power and the ratings are 
> more of a limitation based on the minimum CAT 5 specifications.
>
> Concerning the high voltage and switching DC-DC supply idea, you would 
> have to run the calculation on the efficiency curve of voltage drop 
> and power supply given by the DC-DC converter. The more voltage you 
> drop the more power you loose, so this could be a self-defeating plan 
> and more costly in upfront costs as well as operation costs. Although, 
> most of us could care less about the operation costs; being so little. 
> There would probably be an optimum power draw combination in that 
> situation, which would depend on the characteristics of the DC-DC 
> converter. If you are sticking to the PoE specification, for sure you 
> will never see 13W of power at your Pi, but you could probably make it 
> work.
>
> John Vaughters

You're right, it would be a silly, frustrating exercise (risking the 
escape of magic smoke) to have the DC-DC converter on the "source" end 
of the cable without another regulator on the sink end with a Raspberry 
Pi, so why not just use one on the sink end. I also think that following 
the PoE limits for both power and voltage would tend to keep your house 
insurance company happier.

Another issue we haven't touched on (here, but it's been extensively 
discussed in the past) is the (mostly economic) hazard of having 
expensive equipment hanging off 100 meters of unshielded wire during a 
lightning storm. I'd have to be willing to replace the RPI periodically 
to explore anything like this.


-Pete

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