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Maximum cable length Ulticontroller to PCB

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Hi folks,

working on a new 3D printer. For some reason I need to install the Ulticontroller far away from the Electronics. Using Rumba on this printer, but the panel almost looks like an Ulticontroller clone, almost identical only one button more, connectors are the same. I read a warning about max. cable length between Controller and PCB 30cm, but I need around 80 cm or 50 cm at least. Does anybody know why and how to bypass this problem? Is it because of the higher resistance of the cable or possible interference through other electric signals, so maybe two shielded cables would do the trick. Would be great if somebody could bring light into the darkness.




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A shielded cable will definitely help, but it may not be enough as the SD card's data lines are very sensitive. The SPI bus which is used to connect to the SD card is intended to be an "on-board" communications interface, not for (long) cable connections.

In order to connect two devices via longer cables, you'd need a stronger interface such as RS485 (or USB...) which uses beefier line drivers and is therefore less susceptible to interference.

By the way, shielding isn't as easy as it sounds. You can connect the shield to GND, but that will not help much you if you actually have a noisy GND line (which is highly probable as there are some stepper motors connected to that GND...)

Good shielding can only be achieved if you have a metal frame which is connected to PE (earth). You have to connect the cable shields to PE (machine frame), using a very thick and short connection, not just some small 0.5mm2 wire.

You'd also have to tie the GND line to PE (through a 1M resistor) and put some decoupling capacitors between the two potentials (for high-frequency noise).

Of course you'll need PE available. Using an industrial power supply with a metal frame and a 3-wire connection will be the best way to get to a PE signal. Putting the electronics into their own metal case (connected to PE) also helps a lot.

I guess I'll just stop here - I'm actually not an expert in this matter. I've had some experience with electronics and wiring inside a large industrial machine, but EMI and ESD take a lot of time and knowledge to really be understood and managed.

I'd say you should just try using a shielded cable!

Maybe disconnect the stepper motors if it doesn't work (to remove the relevant interferences). If that doesn't help, then more shielding will also not help.


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Thanks a lot Jonny, that really helped a lot! Sorry for late reply. Sticked my nose a little deeper into ESD and realized that an old friend of mine knows sth. about it. I will take shielded cable for the data connection between the PCB and Control Panel and also for the steppers, to keep the intereferences at a minimum. Will give the longer shielded cable a try and we will see, if it works.

@anon: Printer will get Octoprint, but I want the simple panel I am used to being accessible. I want to keep the cables short, but this means the PCB is in a place, where I cannot reach the Controller with the short cable. Problem is, this machine is a "little larger", large enough for me to sit in it while assembling. Will post more details when it´s finished.


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