A word on cables and connectors: shielded board to board connector / cable combo to replace RJ45

[pawelkosi]

Hi guys,

I am a bit stuck. I have two boards that need to communicate over a cable, the boards are around 2 meters apart. So far I have been using RJ45 sockets and Cat 8 cable but I've run out of lines, plus the cat 8 cables are quite stiff.

I tried to find a replacement for this but it is a real jungle, there are just so many different cables and connectors out there.
If you are using cables for data transfers in your own projects what are you using?

For my project here are the considerations:

• All cables need to be shielded. Noise is a problem. I have been using CAT8 SFTP cables as each pair is individually shielded.
• Preferably I am looking for something flexible but I understand that might be a problem in conjunction with the shielding requirement.
• I currently need one cable with four lines and one with six. Sockets / ports will be directly mounted on both PCBs.
• For my application I cannot use anything like WLAN or Bluetooth, it has to be cable.

I would be very grateful for any help on this and any hints you may have as to what to use.

Cheers!

 

[rjenkinsgb]

What are the signal types, levels, balanced/unbalanced etc?? Is it a fixed installation or will the cables have to stand movement and wear?

My first thoughts would be IDE connectors and ribbon cable, as they are electrically pretty good over reasonable distances; just ground alternate cores. It is available in screened if really needed.
Or D connectors and conventional screened or screened twisted pair cable.

 

[pawelkosi]

What are the signal types, levels, balanced/unbalanced etc?? Is it a fixed installation or will the cables have to stand movement and wear?

My first thoughts would be IDE connectors and ribbon cable, as they are electrically pretty good over reasonable distances; just ground alternate cores. It is available in screened if really needed.
Or D connectors and conventional screened or screened twisted pair cable.

I have two devices on the other end using I2C interface and some LEDs that draw quite a bit of power (LED driver is a primary culprit for noise) - I tried ribbon cable but haven't thought of grounding alternate wires. And yes it has to stand movement. The second board is attached to a human I am researching a medical device that tracks patient movements during a procedure to give you an idea.

 

[rjenkinsgb]

For the I2C interface, a good quality USB cable with appropriate connectors fitted should be good; decent ones have heavy power conductors plus a twisted pair for the data lines. (But a lot of cheap ones only have four very thin, equal, cores).

USB-C cables are available in long lengths and with power ratings - eg. 3A or 60W, but I've never had cause to chop up one of those yet to look at the cable makeup, though I'd expect power cores plus probably three pairs.

That may may be suitable for the link to the portable part, but would it eventually need to be something that can either be replaced or sterilised between procedures?
Or it could be fitted via a gland and a plug at the other end only.
For a chemical proof and ultra flexible type, you could use a polyurethane jacketed "chain cable", the type intended for robotics and machine tools to go around moving assemblies. The core strands are extremely fine, and the PU jacket near indestructable.

eg. This is a type we use, multiple twisted pairs - this two pair screend is 6mm diameter, the photo shows a rather larger 6 pair.

Igus chainflex CF211.PUR Data Cable, 4 Cores, 0.25 mm², Screened, 25m, Grey PUR Sheath, 24 AWG, CF211.PUR.02.02.02 | RS

uk.rs-online.com

Or three pair

CF211.PUR.05.03.02 | Igus chainflex CF211.PUR Data Cable, 6 Cores, 0.5 mm², Screened, 50m, Grey PUR Sheath, 20 AWG | RS

uk.rs-online.com

You probably don't need anything particularly fancy for prototyping, but again if the final thing needs to be washable, have a look at the Lemo FGG IP67 rated circular connectors. There are several size ranges and they are perfect for cables such as those above.

https://www.lemo.com/catalog/ROW/UK_English/unipole_multipole.pdf

 

[pawelkosi]

Those are some really cool options, I like how lemo connectors look like. I actually never thought of using USB cable. I need to read up more about it and see if it will fit with what we wanting to achieve. Cheers mate!