ethernethub
I have a device which needs to connect to one of three devices using ethernet. When one device is connected, the other 2 will be powered down. Power consumption is a factor, so I'd like to use a passive component
Using a RJ45 splitter has failed, I was wondering if anyone has a suggestion for this architecture
Would a single ethernet cable with 4 end terminations work?
Is there anything off the shelf for this situation?
Best regards
This is not a complete answer, but it's a good first step.
I recommend checking the PHY's mode switches. It's probably set to auto-negotiate, meaning the PHY will fall back on a slower data rate if the faster one proves marginal. If you can force the faster data rate, it'll be much easier to debug the problem.
If you are lacking space, you can wire directly the Ethernet cable to the board.
What you are trying to do is to use a cable to transmit the signal from the PHY to the transformer which is not recommended as you still have the DC part of the signal.
But instead of using a RJ45 connector with an integrated magnetics you can put two discrete 100 Mbps magnetics on each board and connect the wire to a simple RJ45 connector, or, if your boards are not too far from each other, use a single Ethernet cable and solder two pairs on each board.
Also, keep in mind that your final Ethernet cable with two 100 Mbps will not be standard !
As an example of Ethernet in a very space-constrained board, I made a board for a 1Gbps PHY only 3.5 cm long and 2.5 cm wide. A FPC ribbon is used for RGMII link to the CPU board and I used a very thin transformer from Pulse: H5120. And the Ethernet cable is directly soldered to the board.
100 Mbps works totally fine but as the RGMII ribbon is very long, Gigabit speed is not working on all boards.
Edit following sbc comment #1:
Here is a picture of my thinking:
Best Answer
The two problems is that while the devices might be turned off, there is still standby power. The ethernet cards can still be active at the base level. Which is why Wake On Lan works.
You could try a 4 pole, 3 position switch. This is the same type of switch used in radios, or more computer oriented, vga switches. Quality isn't always the best.
The better question is why is power consumption an issue? Can't you tap into the power from one of the devices?