Has anyone had any success building a passive ethernet hub with just diodes?

[magic]

So how is the project going?

BTW, does anyone know if there is something special about the recommended diodes?
Wouldn't 1N4148 do?

I'm kinda curious, I would have built a rat's nest prototype myself out of 4148s but I don't have RJ45 jacks.

[Freesurfer]

I have some 1n4148s laying around so maybe I will try tomorrow if I have the time

[Freesurfer]

Ok, I made a prototype on a TCB (Taped Circuit board)(tm) by just twisting the pins and wires together without any soldering, and tried to connect it between my router, laptop and desktop PC.
It does work and all 3 devices can communicate with each other.
However the link only negotiates to 10Mbit and is even slower than that in real world performance. Running a few speed tests it gives me about 1.5-2Mbit from both my laptop and my desktop PC. Packet loss doesn't seem too horrible at first glance but I haven't done any tests or checked wireshark or anything like that.
It doesn't seem like win10 has a straight forward way to check whether the link is full or half duplex. When I try to force it to 10Mbit half and full duplex, they both work and give similar results. Trying to force to 100Mbit does not work at all.

These network adapters are all Gbit ethernet adapter, so the results may be different from what we'd see on older 10/100Mbit cards. Gigabit cards can use features gigabit specific features that 10/100Mbit cards don't have. For example if you have a faulty cable where the orange and green pairs are broken, a gbit NIC can still operate at 100Mbit over the blue and brown pairs which are not even in use on non-gbit cards.

[magic]

This wins "the ugliest circuit of the month" award

BTW, I would try to minimize untwisting of those twisted pairs, so that the diodes carrying any orange/green signal are closely in parallel with the diodes carrying its corresponding white signal. Note sure if you have done that because... tape.

That being said, I'm not sure if it was supposed to work at 100Mb at all. The site I found only mentions 10Mb.

Does anything improve if one of the computers is disconnected?
Does it get worse when speed test runs on both at the same time?

Anyway, I suppose it's good enough for some IoT refrigerator stuff

[Freesurfer]

I agree. It would have been fun to test it on a properly designed board with traces and extra components that maintain the correct impedance and such. Fundamentally I think it could have worked for 100Mbit if designed properly. I believe one of the pages even stated having achieved decent results with 100Mbit.

I did the "best" I could with tape to keep the pairs as close together as possible. I am not too worried about untwisting too much, but more worried about the distance between the parallel wires in each pair.

The circuit is made out of 2 "hexagons" of diodes, layered on top of each other with tape and plastic between the two layers for insulation. If you look closely at the original schematics and reshape the diodes into a hexagon, then stack the hexagons on top of each other, you will see that the corners on the top and bottom layer of diodes line up in such a way that the wire pairs don't need to be split very much. One wires goes on the bottom layer, the other on the top layer with minimal separation of the pairs. So it's not as horrible as it looks, but it's limited how close I can get it with a flimsy circuit like this. hehe.

Yes I tried running a test on both at once, and also with only one computer connected. Doesn't change much whether I only have 2 or 3 devices connected.

But I don't think I will use this for the IoT stuff. I'll find another way to free up some ports on the router. I have 2 routers there. One for a point to point link which is always on (5 ethernet ports, but no wifi), and another tiny wifi router with just a single port that is only powered on while using the cabin. I can just replace this second wifi router with a bigger one with extra ports, and use those ports for devices like the TV and STB. Then have the IoT stuff connected directly to the main router that is always on.

[rsjsouza]

I don't recall seeing a dumb hub operating at more than 10 Mbps half duplex. Too many collisions.

A commercial dumb hub usually has some logic to not only detect collision but also to drop bad ports, but I recall the power consumption was not terribly high, even with all the LEDs (I have one lying around but I just can't find it).

[RoGeorge]

Ok, I made a prototype on a TCB (Taped Circuit board)(tm) by just twisting the pins and wires together without any soldering, and tried to connect it between my router, laptop and desktop PC.
It does work and all 3 devices can communicate with each other.

Since you already have the setup and the cut cables, have you tried if it also works without the diodes?

[tooki]

I don't recall seeing a dumb hub operating at more than 10 Mbps half duplex. Too many collisions.

An Ethernet hub is by definition “dumb” and half-duplex. (Full-duplex requires it to be a “switch”, which is by definition not dumb.)

But indeed, I don’t recall ever seeing 100Mbps hubs. Maybe one existed, but certainly in practice people had moved to 10Mbps switches before going to 100Mbps.

AFAIK mixing media speeds requires it to be a switch (hence the dedicated uplink port on old 10Mbps switches with a 100Mbps port to the backbone), and so this, too, almost certainly meant 100Mbps splitter boxes had to be switches, not hubs. Otherwise it would have made transitioning a network far more difficult.

[Freesurfer]

100Mbit hubs did exist. My first home network had one. And I know for a fact it was a 100Mbit hub. But they seem a bit hard to come by. I am a telco guy so I have been in lots of places with older equipment, but I only really see older 10Mbit hubs perhaps with a mix of RJ45 ports and coax ports.
And I am 100% certain it was a hub, not a switch. But this was around the time when network switches also became more common.

And yes to connect 10 and 100Mbit devices together in the same network you needed a switch. The switch has memory to store a full packet and re-transmit at a different data rate than it was received at. Hubs don't so all devices need to run at the same speed.
Edit: There were also hubs with a mix of both 10Mbit and 100Mbit ports. They were essentially a hub, but with a switch in between the 10Mbit and 100Mbit segment

[magic]

I think I know what's the deal with 100Mb.

According to this PDF, 10Base-T uses ±2.2~2.8V differential pulses and 100Base-TX uses ±0.95~1.05V, which leaves only 0.5V per each side.

Maybe Schottky's would work. BAT81~83 or something of that sort. But then it won't be usable with 10Mb (host will RX their own TX).

[rsjsouza]

I don't recall seeing a dumb hub operating at more than 10 Mbps half duplex. Too many collisions.

An Ethernet hub is by definition “dumb” and half-duplex. (Full-duplex requires it to be a “switch”, which is by definition not dumb.)

Well, not quite. The dumbness is simply to differentiate those from the other, "smarter" dual standard hubs that were common during the transitional period from 10Base-2/10Base-5 (AUI) to 10BaseT era - I was shocked many times by the stupid ground differences between the several hosts connected to these networks (things of a country that couldn't pull his head from his rear end and enforce true grounding on electrical installations, but that is another story).

Indeed the CSMA/CD is half duplex by definition.

[james_s]

But indeed, I don’t recall ever seeing 100Mbps hubs. Maybe one existed, but certainly in practice people had moved to 10Mbps switches before going to 100Mbps.

I'm pretty sure I still have a couple 100Mbps hubs in my box of network "stuff", or maybe I gave them away already since upgrading everything to gig switches, I'm not sure. I know they exist though and I know I had some. Switches were always a lot more expensive than hubs.

[tooki]

But indeed, I don’t recall ever seeing 100Mbps hubs. Maybe one existed, but certainly in practice people had moved to 10Mbps switches before going to 100Mbps.

I'm pretty sure I still have a couple 100Mbps hubs in my box of network "stuff", or maybe I gave them away already since upgrading everything to gig switches, I'm not sure. I know they exist though and I know I had some. Switches were always a lot more expensive than hubs.

Well no, not always, which is why hubs eventually disappeared entirely. The price difference between switches and hubs fell continually until there was none at all, making hubs pointless.