CAN-FD cable

ahwitmer

This week, I received the Duet3HC boards.
The boards can be daisy chained to each other. As cables are not included in the box,
I tried to get information on the required CAN_FD cables. I am planning to connect
3 expansion boards to the duet 3.

What are the requirements for the CAN-FD cables?
Can a normal network cable be used?

Thank you in advance.

Harald Witmer

jay_s_uk

Use ADSL cables.
Preferably high speed ones so they are shielded

Danal

@ahwitmer said in CAN-FD cable:

Can a normal network cable be used?

If by "normal network" you mean an ethernet cable, no. Those have RJ45 connections. The Duet CAN connectors are RJ11, which is common on voice telephone cabling.

Preferred cables will be marketed with terms like "High Speed" or "ADSL" or both. This indicates a shielded cable. I used these: https://www.amazon.com/gp/product/B011SS7LYU/

While you get those cables... It is not in spec... but... I have run expansions on plain/flat telephone wire

Monkeh

@Danal said in CAN-FD cable:

Preferred cables will be marketed with terms like "High Speed" or "ADSL" or both. This indicates a shielded cable. I used these: https://www.amazon.com/gp/product/B011SS7LYU/

Which is very visibly not at all a shielded cable. There is no point in it being - the connector has no shield, the system it is intended for use in has no shield... If a foil is presented inside there unterminated, it's at best useless, probably harmful..

Cabling required should be nothing more than a common two pair cable and 6P4C connectors.

Danal

Agreed on shield. At the same time, these cables marketed as "high speed" are typically twisted pair. Which might be marginally better than 'flat' silver phone cable. Maybe.

Having said all above... CAN is designed to be very tolerant of a poor physical layer, and I'd expect two pieces of barbed wire to run it over a 1/2 meter length like is in our printers. As long as the little skritchy points don't touch.

gtj0

Twisted pair on longer runs will help with noise immunity since it's a "balanced" bus. Just remember that the cables need to be "straight through" and not crossover. Most flat telephone cables are crossover.

deckingman

When I started testing prototype expansion boards, @dc42's recommendation was to use high speed ADSL2 cables. Kenable do a nice range from about 200mm up to many metres

Danal

@gtj0 said in CAN-FD cable:

Most flat telephone cables are crossover.

Burned a couple of hours last night helping someone on the Jubilee discord because of this.

The symptoms can be VERY misleading... because, with two boards, and therefore two crossed over cables, the second board will work as long as it is chained, and that same board will fail when attached alone. Sheesh.

dc42

@deckingman said in CAN-FD cable:

When I started testing prototype expansion boards, @dc42's recommendation was to use high speed ADSL2 cables. Kenable do a nice range from about 200mm up to many metres

Exactly so. A single twisted pair using the centre 2 pins is sufficient. Cables sold as "high speed ADSL" are good for this, they are normally two twisted pairs. One uses the centre 2 pins, the other uses the next 2 pins out.

For UK users, Kenable sells them at prices starting from under £1.

gtj0

@Danal said in CAN-FD cable:

@gtj0 said in CAN-FD cable:

Most flat telephone cables are crossover.

Burned a couple of hours last night helping someone on the Jubilee discord because of this.

The symptoms can be VERY misleading... because, with two boards, and therefore two crossed over cables, the second board will work as long as it is chained, and that same board will fail when attached alone. Sheesh.

HAHAHAHAHA!
Oh...sorry.

ahwitmer

Thank you all for the explanations!

jens55

I know it's an old thread but this cable is driving me nuts. I thought I had ordered the right cable but it turned out to be RJ45 Anyway, I need a 1 meter long cable to go from the 6HC board to the tool distribution board. I am not too concerned about the cable from the tool distribution board to the tool but I wanted a commercial cable to go from the 6HC to the distribution board because it is running in close proximity to stepper power cables. Even running to the tool, I wonder if running in the same loom as the power cables to the tool board would cause interference.
I have had too many mysterious issues with interference (not with CAN FD YET) to try and 'wing' it. I'd rather do it properly from the start.

jens55

Anybody ever try using ethernet cable (as it is made of twisted pairs) and chop off the RJ45 connectors and replace them with RJ11 connectors?
Maybe even break out the unused conductors and use them for feeding power ?

Phaedrux

@jens55 I suppose RJ45 should work provided you've got the conductors lined up for CAN-FD.

Not sure about running power through there as well. I thought you were trying to avoid interference.

jens55

Yes, I am trying to avoid interference but what happens if I run the CAN and power wires from the tool distribution board to the tool. They will be in the same loom so I am thinking that if they can run in the same loom then they should in theory be able to run in the same wire bundle which is just another word for a loom .....
I don't know .... I am asking for input because the last thing I want to do is to fight through sorting out intermittent (because they are never easy) weird issues down the road.

dc42

@jens55 I suggest separate CAN and power wires. For power wires I use red/black twin cable, commonly sold as automotive or speaker cable. For CAN cables there are a few options:

The high-speed ADSL cables that are readily available in the UK use twisted pairs and are terminated in RJ11 connectors. These are perfect for connecting MB6HC, EXP3HC and EXP1XD boards. There are also some US-based listings, e.g. https://www.ebay.com/itm/174276577330.
For short runs to tool boards, telephone or alarm cable can be used. RJ11 connectors and associated crimp tools are available from eBay and Amazon at very low cost.
For longer runs to tool boards I use one or two pairs separated from twisted pair ribbon cable such as this https://www.ebay.co.uk/itm/251792806204 and again a cheap RJ11 crimp tool.

jens55

@dc42, thanks for that. The ADSL cables that are so readily available in the UK are harder to find then hen's teeth over here in North America. Amazon sometimes carries the brand you suggest but they are not currently available.
I have RJ11 connectors and tooling available so I was going to make something up but would have preferred a commercial cable.
I will take your advise and run the power cable separately - thanks.

dc42

@jens55 see https://www.ebay.com/itm/174276577330. I don't know for certain that it has the correct pinout, but it seems likely (i.e. one twisted pair is connected straight through using the centre two pins).

jens55

@dc42, thanks for the link! How do you know that this is a straight thru cable or that it is ADSL2 ?

jens55

Never mind, saw your edit ... thanks !