You'll most likely find that it has a dc-dc regulator converting 5v.12v down to 2.5v or 3.3v for the switch IC. Get a cheap 5-8 port switch and open it up. If autoneg fails (as it probably will in a significant proportion of cases), that will result in half-duplex link too, but I wouldn't want to count on that, since I don't think there's anything about this scheme that will cause it to fail reliably. So disabling autoneg and manually forcing half-duplex is probably necessary for 'reliable' operation. This will result in undetected collisions and corruption. Either link flaps and all 3 redo negotiation (which hopefully fails and you get them all in half-duplex), or more likely IMO only the new device fails autoneg and the other two continue on with their full-duplex link. Since there's no provision for re-negotiation once link is up, I'm not sure what happens when the 3rd device comes up. But it's also possible (especially if there's a timing difference as they come up) that autonegotiation succeeds, in which case you will get a full-duplex link. I'd think that if there are 3 devices attached, they'll stomp on each other's autoneg bursts, and autoneg just fails. So who knows for sure what will happen to autonegotiation here. I have to assume the link-pulses pass through the diodes, or link wouldn't come up at all. (For clarification, it should not be mistaken as an "ethernet economiser" or pair splitter which splits the pairs of a single cat.5/6 cable into two separate ports in each end) Schematics: (above doesn't seem to work, try copy/pasting this): i./RhIgF.gif Of course there is no signal amplification like you would get from a real hub or switch, the impedance matching is probably not ideal, and there's the challenge of 0.6V diode drops which could greatly reduce the max distance. This may be sufficient just for some low bandwidth smart devices and monitoring devices. Googling around there are schematics for fully passive unpowered "3-way" network hubs built only from a bunch of diodes, which in theory should allow you to split a single port on the router to two devices running at 10/100Mbit half duplex. The aim is to keep the consumption from such devices as low as possible. For extra ports I would need to add a small switch, which can easilly draw another 5W on its own. I have an off-grid cabin on solar with a low power router which only consumes around 5W for internet access, which has 5 ethernet ports.
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