Tektyte:LogIT USB & PoE Kickstarter

[tekthead]

Hi Matt and the group,

You raise some interesting points with the POE measurement:

1) in some implementations the spare pairs are sometimes used for power transfer, this may require current monitoring of all 8 wires.

2) The higher power applications (POE+ and POE++) use all 8 wires.

3) Back to back transformers may help, so that you can measure the currents between the center taps?

You also need to make sure that the measuring circuit doesn't interfere with the classification process.

Have you considered using a PD followed by the measurement circuit followed by a PSE? This would be a special mid-span unit?

I hear what you saying about the LTC2946 resolution. 12 bits is equivalent to using a 3 1/2 digit meter at half of full scale. There is a separate ADIN pin which can be used for the lower voltage applications.

The total unadjusted error (TUE) includes, the divider resistor tempco, the reference drift, all over the full operating temperature of the part. Like you say it depends on how much accuracy you need.

I wish you well with your campaign.

Regards,

Jay_Diddy_B

We allow for primary and secondary pair simultaneous measurement. 8 wire measurement is overkill as the current travelling into one transformer pair is the same current which travels out another. In the unlikely event that you have damaged return path windings you will not be able to detect this without full 8 wire current measurement and I did look into having a manual switch for flicking between primary and secondary pair measurement but it was a clunky solution better left to the likes of Cisco (who may need this ultimate level of scrutiny on a production line). These devices could be rewired to be used in this way, with pairs of two LogIT units, for the hardware hacker. If you do damage ethernet transformer windings or suspect substandard parts on a product under development one of the best ways to check this is to use a device like the LogIT.PoE and plug in an identical known good device to cross-check the measurements.

One issue of major consideration though is impedance matched data lines. We have gone to a lot of effort in this area to ensure data integrity. More wires measured means more impedance mismatch. These devices are supposed to be transparent to data so impedance is important.

I can't go into too much more detail but be assured that we have total current consumption covered for PoE devices independent of transformer coil mismatch.

The PoE handshake ID resistances are orders of magnitude higher than the sense resistors so there is absolutely no issues with class identification at all levels from the 7W standard to the less official 92W class.

[jeremy]

2. Linux is doable. I will look into recompiling for Linux as well. It shouldn't be too hard as the software is written in Java. You might have to give me a bit of time to test properly though.

Happy to be a beta tester.

Re. the gear. Actually, my workshop is a little bit better kitted out than the universities main labs. I find is so frustrating working with crappy gear. There is some very nice gear in the RF and optics research divisions at UoM but they aren't readily accessible unless I pull strings.

It was either buy a car or get a nice scope and spectrum analyzer. I chose the latter as my Corolla suits me fine.

I'm fortunate enough to not have to pull any strings to get in the optics lab. But no way I would be able to afford the gear that they have, even if I sold my corolla .

[snoopy]

They should sell it in USD then the exchange rate variations won't kill it !!

cheers

I agree Snoopy but the Australian Kickstarter site uses AUD. US exchange rates have been factored in to an extent but it has still dropped further since costings were done which is unfortunate. Either way, the early bird tier is almost at cost without even factoring in NRE expenses.

Sometimes the costs are outweighed by the desire to make something of quality so this is all a bit of a moot point. This is more of an exercise in making a good tool without going backwards.

This is most unfortunate ! The AUD has still a long way to go before it hits rock bottom IMO.

I too am from Melbourne and in the same position as yourself in getting a product manufactured to sell to a world market. As a matter of principle I would not contemplate selling it in AUD's. There is just too much sourced from overseas and I will not wear any cost due to exchange rate variations that are not in my favour so it's USD for me.

I suppose in your current position you don't have much of a choice which is a real bummer when you are trying to give great value for money. You might have to wear a bit of a loss on this but once you have established yourself then you can call the shots and Paypal make it easy to sell in USD

cheers

[hamdi.tn]

nice project , love it ! the pc interface looks handy , great work 

[tekthead]

nice project , love it ! the pc interface looks handy , great work 

Thanks Hamdi,

We are certainly happy to be making something a lot more useful than exploding kittens.