Electronics that would pass european conformity tests?

Hello there.
I am new to this RepRap project, but i really starting to like it and i am actually thinking about building me a machine once i've sorted out sources for raw materials. And i'm not shure if i should just buy a Kit to get me going, or try to organize the stuff myself... (Not in a hurry, so i'll take my time to decide the best option)

Anyway to the topic of this thread. I was checking out the basic gen3 electronics to see what it offers, and to decide if i could live with it, or if i should invest the time make my own circuits.
Now, one thing that really bugs me on these electronics is that there are basically no protective circuits and no noise filtering components anywhere to be seen. Of course, you can say this is a "hobby-grade" or "do-it-yourself" machine and nobody cares about regulations and standards in this business and to begin with, you wanted to keep initial hardware costs as low as possible.

But i'd like to ask you, is this really the way such a "project for the masses" should be handled? And what about the people that actually want to sell assembled electronics for the guys and gals who do not have the equippment or knowledge to make everything at home?

Well, sooner or later you will run into the EMC (Electromagnetic Compatibility) directive, and probably some other (low voltage electronics) directives that would apply to this project.
Now, one thing that is pretty clear to me is that all this stuff has been ignored in all the electronics generations of the reprap, and as far as i could see, noone ever mentioned it or tryed to do something about it.

My question to the reprap community is if there is any interest or even a plan in adapting the electronics to include at least the basics to approach EMC regulations, or if you want to go on with the current path of adapting basic functionality without thinking about safety, regulations and compatibility?

By "basics" i mean some components like transient voltage supressors, varistors, capacitors, inductors and ferrite-beads to improve noise immunity and reduce emission and maybe redesign the layout by someone who knows how to adress this stuff correctly. It shure would cost some time and a couple of dollars in hardware to implement all this, but saving money on the wrong end will always cost you more in the long run...

(I am not a "expert" in this domain, but i work as an electronics engineer in a company that takes this stuff very serious, so i did have quite some practical experience with EMC design and testing in the past few years)

The project is open source and world wide so it is not targeting any paticular market, so feel free to contribute your recommended changes.

First things first, to remember that a stepper motor doesn't have brushes, therefore little to no noise, other than energizing the coils inside the motors.

Second part is, the Gen3 driver board, the chip has inbuilt shoot through protection diodes.

If you want to you can put 100nF caps over the windings, better yet, find what the resonant frequency will be and use a cap that matches that for each winding.
The frequency is the speed at which the pulses are being sent to the motor, will be quite low, and maybe too low to be bothered with

OK
I do know the project is worldwide, so don't take the "european conformity" as a given reference. It is just that these are the standards i have the most experience with, but in general, there isn't much deviation between conformity in the EMC section for european or international standards. Most of the time it's just a different "wrapper". So, if you target conformity to EN 61000 you basically cover most of the worldwide standards.

As for the second answer, i wasn't really aiming that much at the noise generated from motor brushes. I think microstepping is already helping to keep noise down a little as you are ramping up the current. But you are right, a simple, small capacitor can already help to cut down some of the HF of the fast switched digital signals or eliminate some of the noise picked up. As most of the digital signals get generated by a fast microcontroller, there is always some HF noise to be found, even tho your basic signal seems to be rather slow. I haven't really checked out the extruder controller board, but as you are trying to heat up the machine with a high current PWM directly running into a handwound coil, i think there is quite some potential for noise to be generated there that can influence the rest of your circuits. If you would just try to get a bit of a slower ramping up instead of hard edges, this would already help a lot.

Another important part to look at are the serial interfaces you use. I think it's a good idea to go with RS485 communications, but even they can start to mess with you if you don't pay attention to noise and how to get rid of it. I'd like to have an additional option to use RS485 to interface to the computer too instead of running RS232 lines. With the FTDI Chip it's really easy to make your own USB/RS485 converter, just as most people use it as USB/RS232 converter.

I have already seen a youtube video related to the makerbot project (running the same circuits as reprap) where the guy mentioned something about EM Interference and that you have to keep your wires as short as possible, so there seems to be some kind of a problem source that should get cleaned up. (Think it was the "Weekend-Project" video...)

Have to get back to work now. More input and ideas are always welcome. What i would really like to see is people who actually have EMI problems with there setups, so we could hopefully indentify some of the problematic circuits.

Protonias Wrote:
-------------------------------------------------------
> I have already seen a youtube video related to the
> makerbot project (running the same circuits as
> reprap) where the guy mentioned something about EM
> Interference and that you have to keep your wires
> as short as possible, so there seems to be some
> kind of a problem source that should get cleaned
> up. (Think it was the "Weekend-Project" video...)

Probably about unshielded cables. Keep them short to reduce the risk of getting any EM interferences.

Unshielded cables should be okay with the frequency transmitted on all the wires. (USB is probalby the most critical signal in this project and needs a shielded cable)
What i would aim for is, if you have some kind of crosstalk (probably between power and data wires), filter out the spectrum of unwanted signals, keeping your communications basically safe from disturbing noises. Usually it just takes a L-C-Filter at the input of the board to stop the noise picked up in the wire from affecting your circuit. Cost of the filter? Small capacitor and small inductor / ferrite-bead per in-/output, would add up to a max of a couple of dollars for the entire reprap electronics.
The only case where it would get more expensive is when you have to put filters into high current connections, as obviously the inductors that have to be built for the higher currents get expensive there.

My strategy is always to just foresee these components in a early design stage. If you end up to have a running system without the filters, you can just leave the footprints blank and save the money of the components. If however you run into a problem, you have the footprints and the room on your board to get rid of the problem probably 90% or more of the time without a redesign of the circuit. Just by adding some components to the bill of materials. Redesigning a layout at a later project stage, and maybe even increasing boardsurface to have room for the filters is always worse than having spent a little bit more time in the previous iteration by including the filters in the first place. The "wasted" surface on the board, should you end up to use no filters, is negligible with the size of SMD components and thus won't affect the price for the board a lot. (And i speak of personal experience here...)
The only case where this does not necessarily apply is when you are really restricted on board size, but thats really no problem here.

And another one from me (finally registered )

I took the time to check out the Stepper Motor Driver v2.3 a bit more, especially using the GCPrevue tool to inspect the layout (pdf and png are kinda to low quality/resolution).

Anyway, to make it short and brutal, because of what i saw there i now decided to definately make a redesign of this board. I'll not go into detailed description of what i did not like when i opened the files. If Zach would like to know how someone with a bit more professional background would judge his layout, and what, from my point of view, are the biggest "mistakes", i could however try to do a more detailed analysis later on. The other option would be to just wait and see what i come up with and then analyze yourself what i changed.

I'll start up a new thread where the redesign of the motor driver will be the main theme, so we don't run to far off topic in here.

What kind of noise levels have you been measuring?

Exactly where in the cct are you seeing this noise?

Have you captured an image of the noise?

---

Bodge It [reprap.org]
=======================================

---

BIQ Sanguinololu SD LCD board	BIQ Stepcon	BIQ Opto Endstop
BIQ Heater Block PCB	BIQ Extruder Peek clamp replacement	BIQ Huxley Seedling
BIQ Sanguinololu mounting	BIQ standalone Sanguinololu or Ramps mounting	Print It Stick It Cut it

My rep strap: [repstrapbertha.blogspot.com]

Buy the bits from B&Q pipestrap [diyrepstrap.blogspot.com]
How to Build a Darwin without any Rep Rap Parts [repstrapdarwin.blogspot.com]
Web Site [www.takeaway3dtech.com]