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Prusa extruder mux

Posted by Dust 
Prusa extruder mux
August 21, 2017 08:23PM
Has anyone looked at how the prusa multi material mux works?

This is the best image I have so far found of it



I'm looking for details. Yes I want to build my own, as far as I can tell no details are public.

The principle of how it works is simple enough

The e0 stepper wires (yes after the stepper driver) are muxed by 3 control lines to e0 threw e3 extruder steppers motors
From the firmware the control signals are


            default    1     2     3
E_MUX0_PIN  low        high  low   high 
E_MUX1_PIN  low        low   high  high
E_MUX2_PIN  low        low   low   low

So from this we can see is a binary sequence and potentially there is room for another 4 extruders

From the image we can see a what is probbaly a 1-of-8 decoder but any idea's on what they use to actuly switch the lines?
Would need to be stepper voltages... 12v , does it do 24v?

Im also fairly sure the 4 pin chips are opto isolation

Anyone know anything? (I only started looking about an hour ago)

Edited 2 time(s). Last edit at 08/21/2017 08:33PM by Dust.
Re: Prusa extruder mux
August 22, 2017 01:14AM
Apparently that is the old PCB...

This is the new one



3 relays? himm...

Edited 1 time(s). Last edit at 08/22/2017 01:25AM by Dust.
Re: Prusa extruder mux
August 22, 2017 09:10AM
Looks like it's using relays to switch the output between the different extruders. The risk is that the relays might be switched when the motors are powered, which is bad for the stepper driver and the relay contacts. Presumably the firmware that is intended to be used with this board turns the stepper driver off before switching the relays over.

I think this is a poor approach, and of course it's no good for mixing extruders such as the Diamond. I recommend using a separate stepper driver per extruder.


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