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https://github.com/cscott/extrudrboard2

Proposed revision of Printrbot Extrudrboard for multi-color/multimaterial printing
https://github.com/cscott/extrudrboard2

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Proposed revision of Printrbot Extrudrboard for multi-color/multimaterial printing

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# Extrudrboard2

Proposed revision of [Printrbot] [Extrudrboard] for

multi-color/multimaterial printing



Thing tracker at

https://cscott.github.io/thing-tracker/#/thing/737eb982-b77f-43e0-ae38-4fc30f3e3170



## Description



The latest revision of the [Printrboard] (REV F6) is mildly incompatible

with the original [Extrudrboard],

since the HOTEND A signal used by the Extrudrboard was disconnected

and used to provide an extruder fan output.



Also, multimaterial printing doesn't actually need all of the extra

hotend and thermistor inputs.



This repo contains a proposed "Extrudrboard2" which is compatible with

Printrboard REV F6 and provides up to four additional stepper outputs,

used for multimaterial bowden extruders.  The original Printrboard

extruder stepper is used for the direct drive just before the hotend,

and these additional Extrudrboard outputs are multiplexed and used for

the individual filament options.



As a bonus, I've thrown in a FAN2 output for owners of REV F5 and

earlier Printrboards, which adds an extruder fan output which works

identically to that on the REV F6 Printrboard.



The multiplexing scheme here is inspired by the "[Super Switch]" of

Prusa, and in fact basically the same [Marlin] code (`MK2_MULTIPLEXER`)

can be used.  One wrinkle is that the Printrboard extruder output

(we'll call it E0) wants to be a [Gear Head Extruder] with 127

steps/mm, while the individual bowden drivers (E1-E4, driven by the

Extrudrboard2) may be the lower cost 96 steps/mm [Alu Extruder]s --

or even the short-lived injection-molded plastic extruder.  So some

software cleverness is needed to allow multiplexing different

extruders with potentially different steps/mm rates.






There are two versions of the board here.  The [`Extrudrboard2-thunk.sch`]

files are an initial

prototype that allows you to connect two original Extrudrboards to the

Printrboard using the new multiplexing signal scheme.  It uses some

random logic ICs for the multiplexer that I just happened to have in

my toolbox.  There was a three-unit minimum order, so I've got a couple extra.  You

could also order this from [OSH Park] as shared project

[wLrvnUeh](https://oshpark.com/shared_projects/wLrvnUeh) -- warning,

boards are not yet tested!



If Printrbot decided to actually adopt this "project" as a "product",

they'd want something more like [`Extrudrboard2.sch`], which integrates the

four stepper drivers from the two old extrudrboards into a single new

board.  I actually reused as much as possible of the original

Extrudrboard schematic, components, and component packages, so this

should be highly compatible with whatever manufacturing process

Printrbot had for the original Extrudrboard.







## Instructions



### Choose your build



If you have existing [Extrudrboard]s you wish to upgrade to the new

Extrudrboard2 functionality, use [`Extrudrboard2-thunk.sch`] with 1 or

2 original Extrudrboards connected.  If you are making new boards from

scratch, use [`Extrudrboard2.sch`].



### Assembling `Extrudrboard2-thunk`






Populating the PCB is straight-forward.  Three 7x2 0.1" male headers get

soldered in for "Printrboard", "Extrudrboard #1" and "Extrudrboard #2".

Add three bypass caps.  Values are somewhat flexible, but I used one 22uF

(primarily to decouple `FILWIDTH`) and two 0.1uF caps (to decouple the

logic ICs).  Solder in the 74HC138 and 74HC04; use DIP sockets if you like.

Note that the 74HC238 is actually a better fit here, but I just happened

to have a '138 in my toolbox so I added an inverter chip to make it work.

Likewise, you should feel free to use the LS or other variant of the logic

chips if you prefer: we're running on 5V and low speed, so any version

will do.







### Wiring `Extrudrboard2-thunk`






Use three 2x7 header cables to connect the Printrboard and two Extrudrboards

as indicated.  The tricky part is keeping pin 1 on the cables oriented

correctly, especially as neither the Printrboard nor the Extrudrboards clearly

mark pin 1.









You can connect a hotend fan to the HOTEND A output of Extrudrboard #1.

Pins 1 and 2 are shorted together, as are pins 3 and 4.  You probably

want to use a 1x2 female header on the center two pins.  I've marked

the polarity.







### Additional features of `Extrudrboard2-thunk`



The `FILWIDTH` header is intended to support the Objects with Intelligence

[Filament Width Sensor](http://objectswithintelligence.weebly.com/store.html)

([thing:454584](https://www.thingiverse.com/thing:454584)), at the default

pin assignment used in upstream Marlin.  This is experimental: my

[multimaterial merge project](https://github.com/cscott/3d-multimaterial)

using the Extrudrboard2 doesn't have a place for this, and at the moment

I believe that minimizing distance between the merge and the gear head

drive is essential, so if I wanted to use it I'd likely have to significantly

re-engineer the filament width sensor to minimize the distance it would

add to the unsupported filament path.



The `EXPANSION` header brings all of the unused signals from both the

Printrboard EXP1 connector and the two Extrudrboard connectors into a

convenient place.  The 3 of the 4 HOTEND MOSFETs from the Extrudrboards

are unused (one is connected as an extruder fan output); it should be

convenient to use this header to wire them up to an unused signal from

EXP1 in order to drive some auxiliary load: extra lights, heaters, etc.



### Assembling `Extrudrboard2`



TBD...



### Wiring `Extrudrboard2`



TBD...



## Related



* [Forum discussion for this project](http://forum.monstercafe.net/topic5.html)

* [Multimaterial project](https://github.com/cscott/3d-multimaterial)

* [Repo for original Printrboard/Extruderboard](https://github.com/Printrbot/printrboard)



## License



These designs are released under the

[Creative Commons Attribution Share Alike 3.0] license, like the

original [Extrudrboard](https://github.com/Printrbot/printrboard#printrboard).



[Printrbot]: http://printrbot.com

[Printrboard]: http://reprap.org/wiki/Printrboard

[Extrudrboard]: http://reprap.org/wiki/Adding_more_extruders#RAMPS_using_ExtrudrBoard

[Marlin]: http://www.marlinfw.org/

[Super Switch]: https://github.com/prusa3d/Original-Prusa-i3/issues/29

[Gear Head Extruder]: https://printrbot.com/shop/gear-head-extruder-v2/

[Alu Extruder]: https://printrbot.com/shop/printrbot-alu-extruder-v2/

[`Extrudrboard2.sch`]: ./Extrudrboard2.sch.pdf

[`Extrudrboard2-thunk.sch`]: ./Extrudrboard2-thunk.sch.pdf

[OSH Park]: https://oshpark.com

[Creative Commons Attribution Share Alike 3.0]: https://spdx.org/licenses/CC-BY-SA-3.0.html