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Need advice on DIY POE - to which resistor is the wire allocated?

Former Member

In my current project I'm using 2 Arduinos and wan't them to communicate via an ethernet cable.

 

All that works, and they are communicating through a 30meter cable just fine, Now my next step is to power one of the arduinos through the same cable.

and for that I have these spare ethernet port modules laying around.

image

My plan is to simply unsolder the resistors on both modules and attach a set of wires instead.

Ofcourse only for the 2 wires needed.

 

I find it to be a better solution than to unisolate the wire and pull out the wires from the main cable.

BTW. the cable on the picture is not the Actual cable, that is just a test cable.

 

my question is now,

 

Which of the resistors would you think would be "FREE" I was thinking the blue or brown/red set since they are not

used, but to which resistors are they allocated on this module?

 

Or same question rephrased,

 

To which of the topside resistors are cables 4,5 (blue) and 7,8 (red) connected to ?

 

P.s we can talk about how much voltage actual required to be send down the line later to achieve the 5-7 volts needed.

  • 0

    Hi Martin,

     

    I didn't completely understand the question, but as you probably know, those connectors are 'magjack' type connectors (they have integrated magnetics components - there is not an electrical 1:1 mapping between the soldered pins on the connector, and the wiping contact inside the connector), and so if you're planning to use a spare pair of wires to carry power (i.e. "PoE-like", certainly not PoE according to standards), then you'd need to check the connectors have the ability to be used for this (they may not be PoE-capable magjacks). You could check that by using a multimeter and seeing if you have a low impedance through the connector by buzzing out different soldered pins and the wiping contacts.

  • 0 in reply to shabaz

    Unfortunally I'm to dumb to read the schematics of the actual jack HR911105 but i found them right here. http://www.kosmodrom.com.ua/pdf/HR911105A.pdf

     

    I'm not really worried about standards, because it's just personal/garden use for some sensors.
    I would just prefer to pull the power out of the small module rather than splitting the cable itself.

     

    and was hoping to insert 7v in one unit and pull little less out on the other unit from this area marked with Red circle.

    And to protect the rest of the IC, i would remove the resistor to prevent power being transferred futher than this area.

    image

  • 0 in reply to Former Member

    It is not possible to run power in this manner, the datasheet you have linked to shows there is no wire connection suitable for this - the connector internally has the connections separated. It wouldn't be possible without replacing the connector with a PoE one (even for non-compliant PoE this would still be the case), and it may not fit the same holes in the PCB.

    The only convenient solution is some external in-line hack or to break out the unused pairs externally (I can understand it is not that convenient, but that's the way it goes sometimes).

  • 0 in reply to shabaz

    Ahh I see.

     

    Well then i guess I'm just gonna splice the wires out of the cable in both ends and make it ugly.