Hot-end signal influence 2nd extruder steps

I have an Ormerod 2, with a custom made dual color upgrade. The functionality of all parts have been verified individually.

However, when I tried to do a dual print, I saw a very strange problem, where the 2nd extruder was started at a very slow speed seemingly at random.

After some debugging I found out that the 2nd extruder was moving whenever the 1st hot end was heating up. The PWM signal from the 1st hot end was actually was somehow influencing the extruder step signal.

I checked with a logical analyser, and the 2nd extruder step signal actually had a regular pulses when the 1st hot end was heating (and the 2nd extruder was supposed to be stopped). This was measured directly on the extension header pin without any of my custom hardware attached.

I also had the same problem when using the signals for the 3rd extruder instead of the 2nd, which have me believe that it could be a mixup in my config.g, thus I have pasted it below.

Do anybody have any clue what this might be? Any help would be appreciated

; Configuration file for RepRap Ormerod 2
; RepRapPro Ltd
;
; Copy this file to config.g if you have an Ormerod 2
; If you are updating a config.g that you already have you
; may wish to go through it and this file checking what you
; want to keep from your old file.
;
; For G-code definitions, see [reprap.org]
; 
M111 S0                             ; Debug off
M550 PMy RepRapPro Ormerod 2        ; Machine name (can be anything you like). With DHCP enabled connect to (example) [reprapproormerod2] (machine name with no spaces).
M551 Preprap                        ; Machine password (currently not used)
M540 P0xBE:0xEF:0xDE:0xAD:0xFE:0xED ; MAC Address
;M552 P0.0.0.0                       ; Un-comment for DHCP
M552 P192.168.1.50                  ; IP address, comment for DHCP
M553 P255.255.255.0                 ; Netmask
M554 P192.168.1.1                   ; Gateway, comment for DHCP
M555 P2                             ; Set output to look like Marlin
G21                                 ; Work in millimetres
G90                                 ; Send absolute corrdinates...
M83                                 ; ...but relative extruder moves
M906 X800 Y1000 Z800 E800           ; Set motor currents (mA)
M305 P0 T10000 R1000
M305 P1 T100000 R1000 B4267
M305 P2 T100000 R1000 B4267 
M569 P0 S0                          ; Set X axis direction
M92 E615:615                            ; Set extruder steps per mm
M92 Z800
M558 P2                             ; Use a modulated Z probe
G31 Z0 P340                       ; Set the probe height and threshold (deliberately too high to avoid bed crashes on initial setup)
M556 S75 X0 Y0 Z0                   ; Put your axis compensation here
M201 X500 Y500 Z15 E500             ; Accelerations (mm/s^2)
M203 X15000 Y15000 Z100 E3600       ; Maximum speeds (mm/min)
M566 X200 Y200 Z30 E20              ; Minimum speeds mm/minute
M563 P0 D0 H1                       ; Define tool 0
G10 P0 S-273 R-273                  ; Set tool 0 operating and standby temperatures
M563 P1 D1 H2                       ; Define tool 1, uncomment if you have a dual colour upgrade
G10 P1 S-273 R-273              ; Set tool 1 operating and standby temperatures, uncomment if you have a dual colour upgrade

Which firmware fork and version are you using?

What version Duet are you using? If it isn't a Duet 0.8.5, are you using a DueX4 or a Duet Shield to drive the second extruder?

It's hard to diagnose the problem without that information, but my guess is that you have a DueX4 or Duet Shield and the ground wire between its power input terminal block and the one on the Duet is far too long. See my blog entry on my dual colour Ormerod upgrade for how it should be wired.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks for quick and informative help dc42!

Due to your comment I took a new look at the wiring in my solution, and shortened the 12V and GND wires between the different parts of the electronics, and now it works great.

I guess I underestimated effect of the hot end current had on the other signals or something...