POES: Power over Ethernet System.

To the right you see the POES product. This is one set but both units are identical in construction. One unit splices the additional signal into the unused pairs of the UTP cable and the second units takes the signal off again. The RJ45 socket closest to the LED is always the active socket (for putting on or taking off the extra signal).

Each POES unit (half of a set) contains:

The PCB has double weight copper (70 um instead of the usual 35 um), silkscreen on top and soldermask on bottom.


Circuit

The circuit and the general idea are simple. It is based on the wiring scheme of a normal UTP cable. Pins 1, 2, 3 and 6 are in use for data transport. The pins 4/5 and 7/8 are not in use. Pins 4 and 5 make up one twisted pair. Pins 7 and 8 make up the second twisted pair. In POES I use these pairs for carrying the auxilliary signals.

J2 is the input connector. This is what comes from your router, modem or gateway. J1 is the output connector. It carries the ethernet signals which are copied from J2, plus the signals which are supplied by connector X1.

The 'incoming' UTP cable 'sees' a normal UTP cable. What enters at pin 1, leaves at pin 1 as well.

After the stretch of UTP cable which was inserted in socket J1 is at its destination, a second POES unit removes the signal again. The loaded cable is inserted in socket J1 again and the previously added signal is removed from the UTP section and supplied to the X1 connector on the second POES unit.
On J2, the unmodified Ethernet signal (as compared to the signal entering J2 of the other POES unit) is present again.

Each POES unit has room for a capacitor with a 5 mm pitch. You can mount a 47 nF one for filtering or a 10 uF one for buffering. If you need one.
Each POES unit also has a two colour LED attached over the auxilliary signal, via a 1k5 resistor. At 12 Volts this resistor limits the current to 6 mA. If this is too much of a load, just cut the LED off the board. But it comes in handy. Both POES units need the colour of the LED to be the same.


Result

This is the POES set again, but now one is turned upside down to reveal the bottom side of the PCB. It has a big ground plane, plus sufficient width for the signal lines. To enhance the reliability, the copper weight was doubled when compared with traditional PCB's. So in effect, the tracks are twice as wide as you see them.

The light gray thing on the left is the RIA Springcon connector. Lift up the black wings and you open the clamp of the terminal block. Insert the cable and lower the springloaded clamp again. The wire is securely gripped by two planes moving in parallel. It clamps thin wires just as good as fat ones. I tried it with wires of 0.14 square mm upto 1.5 square mm. This is the best wire gripper I ever experienced.
Plus: you need not find your screwdriver when working in the patchpanel and suddenly needing to remove one or two wires. Just lift the lever and you're done. These are truly revolutionary wire clamps!

For POES only the best is good enough.


Operation

Let's assume you have a router (with it's own dedicated wallwart power supply) that needs PoE delivered via the UTP cable. Operation now is very easy:

PoES Competition
  1. Determine how much power supply cable you need at the receiving end
  2. Cut the wallwart power supply cable to size
  3. Split the cable ends and strip them
  4. Insert cable ends in the Springcon receptacles
  5. Connect enough UTP cable
  1. Determine how much power supply cable you need at the receiving end
  2. Cut the wallwart power supply cable to size
  3. Split the cable ends and strip them
  4. Solder a 2.1 mm barrel connector to each end
  5. Insert the barrel connectors in the PoE boxes
  6. Connect enough UTP cable


That's it! No need to tediously solder 2.1 mm barrel connectors to both cable ends. Just stick the stripped wires in the no tools required PCB connectors and close the latches. If you are skilled, you only need a sharp hobby knife!

The soldering of barrel connectors is very time consuming and it needs special tools (soldering iron) which needs to be brought to the work place. This is a waste of time and money.


Bill of materials

Here is the BOM (Bill Of Materials) for the POES device. The table speaks for itself.

Part Description Amount Price Total
PCB Printed circuit board, double copperweight, fully masked 2 0.65 1.30
RJ45 Heavy duty 8P8C RJ45 connector, unshielded 4 0.36 1.44
SpringCon RIA Springcon 2 terminal block, no tools required 2 0.30 0.60
Resistor Current limit resistor, metalfilm, 1/4 Watt, 1500 Ohms 2 0.08 0.16
LED Two colour, two pin, LED, brand Kingbright, model L-937EGW 2 0.12 0.25
Total for the hardware 3.75
Profit Engineering charges 1 3.25 3.25
Total for one POES set 7.00/td>

Shipping charges: € 1 for each POES set plus € 2 for handling and wrapping.


Bottomline

As you can see, my engineering charges are modest. If you feel my charges are too modest, you are free to change the amount, but only with a reasonable amount.


Page created on 21 November 2007 and

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