Re: Mach2 USB

Dale Ghent

Yeah a big advantage with ethernet is that you can easily crimp your own cables. I wired my house with cat6 (I actually do run a 10Gb ethernet network here). I've got a few hundred feet of cable in my basement and just crimp a new cable when I need it. Monoprice has a line of slim format stranded pair ethernet cables that are a dream to work with inside of cabinets and other confined spaces that need only short runs[1].

But there are some drawbacks to ethernet. Driving the ethernet PHY and magnetics is power hungry compared to USB. In fact, it takes so much power relative to other communications types that a standard called Energy Efficient Ethernet (EEE)[2] was developed so that, on parts that support EEE, they can be driven at lower power levels while maintaining desired link speed. The use case for this is short runs, where you don't need to send ethernet frames down a 100m long run of twisted pair. But both ends of the connection need to support EEE, not just in the hardware PHY, but also in the OS drivers.

Another thing I don't like about ethernet, in the context of astro gear mounted on moving things, is in fact the captured mating of the design. With USB, you have a good chance of a cable snag just pulling the connector out of the socket. With ethernet, it's not going anywhere, and the lack of it releasing may cause things like the device's ethernet socket getting ripped off the circuit board. So I prefer a friction-based capture, but it can't be too weak or too strong. I think the best solution is something that is magnetically attached, a la Apple's MagSafe concept but with a stronger magnet holding things together.


On Jul 23, 2022, at 13:38, Sébastien Doré <sebastiendore1@...> wrote:

Better? Definitely a BIG YES !

• They were designed from the ground-up for high bandwidth, low cross-talk, medium haul data transfers. RJ-45 is also a captive mating type the can't be unplugged by simply pulling on them (with reasonable force) without releasing the latch.
• Contacts are much better "tension-loaded" (not sure its the correct terminology) so there is less chance of breaking them with temperature fluctuations, vibrations, etc.
• Their max mating cycles are still in the many hundreds (alike USB) but some good quality ones come in excess of a few thousands:
• They are much easier to DIY than USB if you're that kind of person.

• They are length-limited to a whopping 100 meters (vs a fews meters for USB) before requiring any signal reconditionning (hub/switch/extender/access point).

• And another advantage IMO is their ability to carry significant power (with PoE). Replace two cables by one and provides up to ~70W (5.8A at 12V) at the end device (latest 802.11bt type 4 standard). Enough to power most cooled cameras, a focuser, FW, etc.

I don't think they were designed for outdoor use explicitly, but their characteristics and the fact that they do come in ruggedized/weatherized versions (much like the power/motors/encoders connectors on the CPs - link) makes them a better choice IMO. RJ-45-terminated CATx cables even come in UV resistant / direct burial types that are grounded/shielded at the connector, providing better EMI/EMF immunity. To be fair, USB does too to some extent nowadays, but its not what manufacturers put on their devices unfortunately... And they are harder to source in my experience.

That's not even talking about the benefits of the the protocol resiliency to data communication errors...

De : <> de la part de Roland Christen via <chris1011@...>
Envoyé : 23 juillet 2022 11:10
À : <>
Objet : Re: [ap-gto] Mach2 USB

Are Ethernet connectors any better? Were they designed for outdoor use?


-----Original Message-----
From: Sébastien Doré <sebastiendore1@...>
To: <>
Sent: Sat, Jul 23, 2022 6:48 am
Subject: Re: [ap-gto] Mach2 USB

Le 23 juill. 2022 à 02:38, Christopher Erickson <christopher.k.erickson@...> a écrit :

The IEEE USB specs say they should be good to several hundred connects/disconnects.
Exactly my point, so don’t expect to get more out of them.

Roland Christen

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