[Arm-netbook] designing a low-cost decent 3d printing board

Luke Kenneth Casson Leighton lkcl at lkcl.net
Tue May 23 02:27:24 BST 2017

hi all,

ok so i've been looking around and the practice of creating a
"modular" 3d printing electronics board is extremely common, thanks,
many years ago, to the stupid, stupid decision to use prototyping
(evaulation) plugin boards with 1.3 to 2.0 *amp* stepper ICs mounted
onto micro-postage-stamp-sized PCBs.  the problems these cause are

*some* people have actually read the datasheets associated with these
driver ICs and have designed PCBs that respect the advice of the
designers, by making sure that a large part of the PCB's copper is
used as a heat-spreader.  however the practice is not very common, and
the people who make such boards are typically actual well-trained
electronics engineers from the west, but who then use western PCB
manufacturing and assembly plants, end result: very expensive boards
($120 to $200).

as i would like to see both a low-cost board made *and* have a decent
design, and having researched this for many weeks and found that what
i am searching for DOES NOT EXIST i need some help.  the board i
believe is best started from is the Duet WIFI:

this uses 2.5A TMC2660 "silent" steppers and importantly they're
SPI-based.  the idea is to cut the DuetWIFI down to the *absolute*
bare minimum, turning it into the exact same thing as TRAMS (which
uses the 1.3A TMC5130).

so instead of an on-board ATSAM4, you use an arduino due.  instead of
WIFI you use a *standard arduino WIFI shield*.

now, debatable is whether to split out the MOSFETs, endstops and
thermistors into their own separate shield as well, which i feel might
be sensible.

in particular i would very much like to "stack" the steppers because i
have a design where it is going to use *four* z-axes.  in a first
iteration those may be wired up as 2x 2-serial in parallel, however it
would be very *very* nice to be able to just add a second "stack" of 4
z-axis steppers and use them to do automatic bed-levelling.  so to do
that it would mean having on-board jumpers that could select
alternative GPIO pins... or maybe to use an I2C-based or SPI-based
GPIO expander in order to reduce the amount of GPIO needed.

however an alternative idea which would do just as well (without
needing too much work) would be to have the expectation that there
would be a "base board" into which *two* modular 4x TMC2660 stepper
boards would be plugged, and an arduino due, *and* the
MOSFET/endstop/thermistor board, and the *base* board would take care
of GPIO expansion.

anyone considering this: the layout on the DuetWIFI for its steppers
is very *very* specific and should really not be touched or altered,
merely cut away surrounding parts and add the necessary
arduino-compatible headers.

any takers for what is likely to be a quite straightforward project?


crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68

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