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Comment by numpad0 | Hacker News Reader

This isn't a desktop Ethernet switch. Lots of robotic parts like industrial cameras and fancy laser sensors use Ethernet for interfacing instead of USB or RS232C. Doing so solves cable length limitations and connection stability issues of those peripheral buses. There would be penalties and overheads of (mis?)using inter-node communication protocols like Ethernet (and TCP/IP), but those tradeoffs are completely acceptable.

What is not acceptable is full sized switches inside of a robot: they're way too bulky. You may be looking into installing a switch inside a humanoid upper arm or inside pelvis. Regular switches and hubs don't fit there.

This product solves that specific robotics packaging problem. Electrically it's a switch/hub, physically it's much smaller than that, that's the point.

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I wonder if you could do away with the switch and just daisy chain in many of those applications. It seems to be forgotten that ethernet supports this.

It's not exactly forgotten. There's 2 wire Ethernet/PoE standard (used mostly in automotive) that can be daisy-chained. Designing for it however is non-trivial and few third party devices (again outside automotive market) support it.

Hmm... I thought everything still had collision detection and would work on a bus, like what you'd get using a hub.

There is normally no collision detection beyond 10Mbps. Also PoE would not trivially work daisy chained.

100base-Tx is specified for shared media (hub rather than switch), but I think you need some electronics to make a hub, you can't just do a passive connection, and so you probably end up with a hub IC and may as well use a switch IC instead.

It might work in so far as you'll get packets through. The performance would be abysmal, though. Modern Ethernet is built around switching.

Would it really be that bad? If the devices were well behaved (ie. not too noisy, no gratuitous ARP etc) and the application could assume that most of the time either zero or no devices will be communicating, would it be that bad?

This is something I might test myself. I have a couple of audio devices that will never be both "active" at the same time. In my current layout I need to run either two cables or just another switch and it just seems a waste. I wonder if I can buy daisy chained cable so I don't have to make one...

Our company is often asked at expos if we supply 2 wire ethernet switches (e.g. Single Pair Ethernet SPE[1]) but the reality is there's little demand (outside of automotive) we see in the Industrial marketplace for this type of product.

The other issue is that there is at least 2 competing industrial connector standards for SPE, the main ones being from Harting[2] and Phoenix Contact[3]. I think this could be a great option for the future and ultimately lead to lower cost cabling and smaller products.

[1] https://www.single-pair-ethernet.com/en

[2] https://images.app.goo.gl/ND9d9x66YNUckS7g6

[3] https://images.app.goo.gl/yWAiUAx4Y5vRmmbZA

Yeah that's the thing: neither of them is really standard, and both are fairly expensive. They are also available in very limited mechanical configurations (angle, mounting). Fortunately SPE does not really require either of them. In our product we're going with our own solution.

> Our company is often asked at expos if we supply 2 wire ethernet switches (e.g. Single Pair Ethernet SPE[1]) but the reality is there's little demand

This reminds me of a funny conversation I had in a small town stationers when looking for an item.

‘No, we don’t stock it. People keep asking, and I keep having to explain that there is no demand.’

Though this wasn’t for an obscure Ethernet variant.

ha, true! However at expos often the person asking is a vendor looking to sell SPE components to us, or someone in the industry trying to determine if a technology is popular. Can be a bit of an echo chamber.

In industrial IO, including robotics, the norm these days is 3 port switches embedded into devices, specifically to support daisy chaining.

Hubs are no-no because of various performance issues, including how more and more gear supports gigabit on the daisy chaining.

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