Standard Interface for Extruders

I would like to propose a quasi standard for an extruder interface. The idea being that the entire extruder can be switched out by simply disconnecting a single connector.

On the extruder, I'm proposing a DB-9 Female connector with the following pinout:

1 - GND
2 - Resistor/NiChrome/Etc... Return (+)
3 - Thermistor/Thermocouple Return (+)
4 - Fan (+)
5 - Accesory (+) (Could be a light, another fan, another heater, or something else)
6, 7, 8, 9 - A+/A- B-/B+ Stepper Coils

Does anyone see problem issues with this idea?

I've done something similar with EuroStyle connectors, but they are hard to unplug, and a bit bulkier than I like.

You don't want a common ground. The thermistor / thermocouple must have it own ground connection. Otherwise the heater current will cause a small voltage drop in the ground lead that will totally screw the temperature reading.

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[www.hydraraptor.blogspot.com]

Is a DB9 connector rated for 2A?

It may be better to have two plugs, with a separate one for the motor. We already more-or-less have a standard for the motor plugs, it's a .1" (2.54mm) spaced female plug designed to plug into the top of the pololu motor driver carrier, and this method is outlined in the RAMPS electronics specs. I think most (?) of the other electronics use something similar.

I was thinking along similar lines, but I'd prefer to have a plugable terminal strip, like this where it's got a higher current rating (heater requires fairly high current) and it's screw connected. That way I can buy (or sell) an extruder that's easy to plug/unplug but also doesn't require any soldering to connect to any set of electronics you please.

Chris is right about a separate ground for the thermistor - it's hooked to "AGND" on the chip and should be kept away from all that noisy high-current PWM in the motors and the heater. I.E. a shielded 3 wire cable with +5 (AVCC) ground (AGND) and signal (analog 0, usually). And the shield should be grounded (at one end only) to regular ground.

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I'm building it with Baling Wire

I kind of anticipated that to be the case with the thermistor.

As for the motor connection, I'm only referring to the extruder end of things. I just preffer a nice clean terminated bundle of cables on that end. The RAMPS end is a total rats nest, but that's fine.

DB-9 is probably not the best choice out there, but I'm considering what is easy for most people to source with little effort. 2A is probably fine on a DB-9, rated or not. The fact that I cannot share GND means no accessory though... DB-15 is also a possibility. I could spread the amperage over two or more pins there:

1,2,9 - Heater Block +12VDC
3,10,11 - GND
4 - Fan
12 - Light
5 - Spare, or Z-home four-point contact for leveling beds, etc...
6-13 - Thermistor
7,8,14,15 - A+/A-/B+/B-

In reality, standard ribbon cables/connectors are just about the most widely available. If oriented properly, they can survive repetitive stresses quite well, too. Also, you can leave every other strand unused and grounded to act as a shield.

The most unreliable parts of my machines are the connectors. I am currently switching over to screw terminal blocks and ferrules.

The XY table on HydraRaptor uses DB9 connectors and they have been reliable, presumably because they screw together and have proper strain relief on the cable, so there is no chance of any movement. Simple 0.1" SIL connectors and ribbon connectors simply do not work in the environment of the machine.

Edited 1 time(s). Last edit at 04/30/2011 04:16AM by nophead.

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[www.hydraraptor.blogspot.com]

Use pin 1 ground for thermistor and the connector body as a ground for everything else

Quote
jgilmore
We already more-or-less have a standard for the motor plugs, it's a .1" (2.54mm) spaced female [...], and this method is outlined in the RAMPS electronics specs. I think most (?) of the other electronics use something similar.

RAMPS is about the only set of electronics using this plug? Gen2, Gen3, Gen7 use a 4 mm spaced one and quite a number of electronics "experts" strongly prefer screw terminals spaced at 0.2" (5.08 mm). Gen6 uses a proprietary one.

That said, if we want to go the multiple extruder way, we probably also want to do something like a tool changer soon. How about something similar to the USB plug, in a printed housing, of course.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

The problem with using screw terminals for this is that it defeats the purpose, which is to have a quick disconnect for everything on the extruder. As I mentioned in the top of the post, I've already tried using Euro-Style connectors for this purpose. The connector fit on a ten contact block is just too tight, and creates a risk of damage to the extruder and stage during removals.

Again, I'm not talking about connectors on the RAMPS/GENx end of the cable. What I am suggesting is a connector that is fixed to the top of the extruder, what ever extruder/(other device?) that may be.

jcabrer Wrote:
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> The problem with using screw terminals for this is
> that it defeats the purpose, which is to have a
> quick disconnect for everything on the extruder.

Have you looked at pluggable terminal blocks? All the benefits of a screw terminal, and quick disconnect/exchange etc as well.

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I'm building it with Baling Wire

I have pluggable terminal blocks now. It was the first attempt. The problem is that the fit is really tight, and this can lead to damage when trying to disconnect.

How about using an edgecard connector?

An edge card connector requires skills (PCB etching), and components (edge connectors and crimping tools) that are not readily available to RepRap builder at every level. If it's going to be a standard, it needs to be somewhat within reach for the average person.

The benefit of using DB cables are many. DB-15 and DB-9 connectors only require soldering (assuming the pins are fixed), and the shells already come with strain relief, there would only be one cable going to the extruder.

Why cant we design and print a screw terminal style connector that uses m3 screws/nuts/washers to clamp the connections. Then all you need is the fasteners.

Hi Greg,

That idea has some appeal to me, but keep in mind that we are talking about ten (10) or more terminals that have to be screwed and unscrewed whenever you want to change out an extruder. Not to mention the risk of wiring something up wrong after many changes.

I'm actually looking at your most recent extruder to see where I can put a DB-15 on standoff. A shim between the stepper motor and the extruder body seems like a posibility, but that stepper mount is pretty thick already. I'm rusty on my OpenSCAD at the moment. I got lazy and started using SolidWorks. If I can figure it out, I'll make an addition to the design and illustrate what I'm thinking about.

In the mean time, keep those ideas coming!

BTW: Your extruder design really embodies the spirit of where I want to take all of this. Simple, elegant solutions.

I like the edge connector idea. Maybe an alternative would be to modify USB connectors. They pretty much are just a fancy edge connector. I also know how much temperature the jacks can take/sink because those suckers are crazy difficult to salvage. If you embed the jack into the filament feed itself you could literally plug the hotend into it.

Another random idea.. Bullet connectors embedded into a PTFE rod in a standard arrangement. If small bullet connectors are used you can probably just crush/crimp them.

jcabrer Wrote:
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> An edge card connector requires skills (PCB
> etching), and components (edge connectors and
> crimping tools) that are not readily available to
> RepRap builder at every level.

Take a look at your computer's motherboard. The PCB etching skills are the same as needed for etching all the other PCB boards. The connectors are as readily available as chips, and typically from the same suppliers. They typically surface solder, just like chips, but we'd need to use ones with at least a few through holes for strain relief.

This is indeed beyond the skills of many users, but no more so than any of the other electronics.

> The benefit of using DB cables are many.

Agreed. However it won't be possible to have the machine switch extruder heads all by itself, which as I recall was one of your design goals. I don't know if edgecard connectors could be found that allow that, but it shouldn't be too hard to design one using one side of an edgecard socket for the contacts.

The card edge connector can't be standard if everyone has to make their own.

> Agreed. However it won't be possible to have the
> machine switch extruder heads all by itself, which
> as I recall was one of your design goals.

Not one of my goals. Somebody else. I just like swapping out extruders for PLA and ABS easily, not automatically.

How about something along the lines of a diy zif/edge connector? Basically, two pcb's, one inverted over the other and mechanically snapped together with either a spring contraption or mechanically that would be operated automatically when slotted together. I've never owned a zif connector so I have no idea how they actually work.

I'm considering the following;

[www.winfordeng.com]

This one, not so much, but the screw terminals are attractive...
[www.gravitech.us]

And this one is great, if a bit on the pricey side
[www.winfordeng.com]

All of these links make it two connections at the extruder... what is wrong with directly soldering to a standard bucket DB9 connector?

I like the Idea of having a standard plug in connection.><

DB9 is well proven standard.

I think its still quite a bulky connector for hanging off the extruder there must be some thing better that could be used.

Maybe spade connectors or bullet connectors as used in cars for extruder element power with another 4 way connector for lights / temp sensor connections this would make it less bulky and keep the sensor wires away from any high curent switching noise.

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