Common lines for compact wiring

Tryptamine

Dear Forum,

I am rewiring my printer as I am switching to a new carriage and cable chain.

My plan is to get rid of as many cables as possible.

This means i will use a common ground, from measurements i found out fans use a common high line instead, i suspect this is duet to the PWM being controlled by MOSFETs.

So my approach would be to wire one common VIN (fused!), common 5V and GND to the print carriage and build a splitter there.

both Fans use the VIN, to the board go only the negative connectors
Heater cartridge same story
LED lighting uses common GND and common 5V line
Optical Endstop common GND, common 5V and one data
BLT same story
what about thermistor? Probably common ground?

Is there any problem with this approach or am i missing something critial?

Thanks in advance!

deckingman

@Tryptamine You are correct that pwm switches the 0v side. So anything that is PWM controlled has to have a separate 0V connector but they can share the positive side if they use the same voltage. Thermistors are just resistors but usually work in a voltage divider circuit so I'd have thought that neither leg is common to anything else but no doubt someone familiar with the circuit diagram of the board will correct me on that.

dc42

@Tryptamine the thermistor can't use a common ground with other grounds because Duets separate the analog and digital grounds, for better analog performance.

The endstops, LEDs and BLTouch can share ground and +5V lines although there is a possibility that the transient current generated by the BLTouch when the pin extends or retracts could cause false triggering of the endstop or LEDs. If that does happen, it can probably be solved by adding a decoupling capacitor between 5V and GND at the tool head.

Fans using VIN voltage and heaters can indeed share a common VIN wire.

If you are using Duet 3, have you considered using a tool board to reduce the number of wires needed in the cable chain?

Tryptamine

Thanks so much for these replies!

I did not know the Duet tool board existed.
Sadly I am still on the Duet 2 Wifi so the toolboard is not compatible.

But probably my reduction to common Gnd, Vin and 5V and a splitter board on the printer already is enough so I can fir everything in the 7mm cable chain.
And I also love the ide to be able to unplug stuff on the carriage board and not having to undo all cabling when changing one component.

@dc42 @deckingman
I'd love to upvote you, but due to reasons beyond my understanding, I have -1 reputation and can not upvote.
so just thank you

dc42

@Tryptamine your reputation is currently 2.

droftarts

@Tryptamine said in Common lines for compact wiring:

I'd love to upvote you, but due to reasons beyond my understanding, I have -1 reputation and can not upvote.
so just thank you

You got downvoted in this thread: https://forum.duet3d.com/post/291888

Hopefully with this wiring change you’re fitting a 24V heater? Did reordering the config fix the PWM issue in that thread? You never replied.

Ian

Tryptamine

@droftarts I have the 24V heater since a long time already The problem back then was i had all my wires through a cold water connection hose and could not change single parts.

And also, even though I planned to change the heater block anyway, I can not accept a problem to be just "unsolvable", especially with software. I thought there must be a way, just for my ego so to say.

Indeed it was your approach M307 H1 ... after the M950 H1 ... that solved the issue!
Big times thank you for this again. Made the printer last for some important prints before the heater core swap.

I understand the safety concerns, but for me, it makes no sense to destroy someone's reputation because he asked for advice.

Thanks for helping out on this one and for the upvotes!

I will update you when my new carriage and daughterboard are finished.