I don't have a specific circuit to suggest. The Wikipedia page on current sources is a good introduction however. I was trying to make two points: 1) we rarely use current sources in our designs so we all automatically think about controlling voltages. In this case, PWM of a voltage supply to regulate power applied to a resistor based on thermal feedback. That's fine. But we can also use currenby TC - General
rocket_scientist, did you actually test the circuit you made? If yes, do you have results to report (other than your discovery of shorter than expected trace length)? There is something I am wondering about based on your messages. I certainly understand that we are talking about multiplexing zones. But I get the impression that your plan is to PWM a voltage supply rather than a current source. Iby TC - General
I've sent messages via the forum's private message feature to people that clearly indicated that they want to collaborate on the development of ARM-based electronics for Mendel. If you didn't get a message from me and you are interested in this collaboration then please send me a message. Thanks! TCby TC - Controllers
aka47 - what is the "BEEF experimental platform"? More generally, I'm wondering what improvements could be made after completion of the proof of concept. So, if you had to make a list of incremental improvements for Mendel electronics what would you put on the list, and what priority would you assign to them? An example might be stepper motor drivers that can handle XYZ amps without overheatingby TC - Controllers
Annodomini2 - For step 1 I am thinking of using an off-the-shelf development board + a hand-built vero board to adapt the ARM microcontroller to the rest of the electronics. I don't think it would be difficult to do this for a small set of boards for development purposes. I've surveyed many of the LPC176x development boards and even own a few different ones. Once a preliminary plan for the hardby TC - Controllers
A couple of you have expressed interest in collaboration and that's great! We need to connect outside of the forum and I'll try to get in touch with you. You can also try to get in touch with me via the forum's private message capability (assuming it works). TCby TC - Controllers
Quite frankly, I don't get all the political rhetoric and I fail to see how this sort of discussion will help us (or maybe just me) make progress. TCby TC - Controllers
Julie - I always appreciate feeback, pro or con. That doesn't mean that I always agree with it however. Here are some specific points that I don't agree with you on: "Seems like a step backwards." I simply don't get your perspective. We'll just have to disagree on this one. "Counter proposal..." This doesn't make forward progress in my view. I believe that it is important to overcome some of thby TC - Controllers
My gut on developing new electronics is to take a three step approach: 1) map the existing solution onto an ARM Cortex M3 microcontroller such as NXP's LCP176x family 2) design and have manufactured an integrated single board RepRap controller 3) develop a extensible/expandable system My rationale is... 1) Moving to an ARM Cortex M3 overcomes performance and code density issues without addinby TC - Controllers
rocket_scientist thanks for the specific and constructive input. Exactly what I was looking for. I'd love to see others respond as well. I'll have to see what mccoyn is up to with his electronics design. My gut is that something simple and cost-effective is the way to go for the near term to help lower the hurdle of construction/adoption. Longer term, an approach that would facilitate experimby TC - Controllers
I've seen adhesives that go much higher than needed but I'd have to dig again to find them. However, I wonder about the use of glass as a heater bed since it doesn't conduct heat very well. TCby TC - General
So, I've read what everyone has written to this point. As one would expect, there are plenty of opinions about what the solution should be. Some of it is based on solid arguments and considered thought, and some of it is more off-the-cuff (which is fine). But, before moving down any specific solution path I think it is more important to define the problem that we (collectively) want to solve. Iby TC - Controllers
So, after further searching I think this is "EMC"... Is this right? TCby TC - Controllers
Anodomini2... RE: item 5 - what do you mean by "EMC"? Electro-Magnetic Compatibility is what comes to mind for me (an EE), but I don't think that is what you meant. Building an extensible/expandable system will complicate and slow down development significantly. Note that I am explicitly NOT saying the end result will be, or needs to be, complicated. It is simply that it takes time to clearlyby TC - Controllers
I think there are a few benefits of the serpentine etch approach: - simple fabrication - easy to obtain materials - multi-zone temperature measurement and control - low cost The idea is to use the serpentine etch to function as a heating element and also for temperature measurement (resistance varies with temperature). I'd guess that insulating the bottom side would help a fair amount. Howeverby TC - General
nophead's experiments are very interesting indeed. When I posted my questions about peak power / average power I wasn't thinking about the whole problem, and in particular, how to make multiple zones cost effective. The point is that to minimize the amount of electronics needed then an approach where the the zones are multiplexed is likely to be necessary (i.e. time-slice and turn on one zoneby TC - General
I know this topic isn't too active at the moment but I was interested enough to read it through top to bottom. One thing that isn't clear to me is the "shield" concept. Can someone point me at a description, drawing, or picture that would clue me in (as I'm clueless at the moment). Thanks! TCby TC - Controllers
annodomini2 Wrote: ------------------------------------------------------- > I'm in TC, i'm an Embedded Software engineer so we > have two bases covered. > > Shall we setup a working group? I'm happy to see the interest in a collaborative ARM development. I think a new group would be best since there will be many aspects to the development that would then be topics under that grouby TC - Controllers
Found another interesting item for a nozzle. Do a search for: Grex Tritium Nozzle 0.5mm Made for airbrushes, easily obtained on Amazon and other on-line retailers. Available in other sizes. TCby TC - General
How much power is needed for the heated bed in total (watts)? I would think there should be a reasonable peak power that is needed to heat the bed up at a decent rate and a nominal power level needed to maintain the bed at an even (hot) temperature. With a multi-zone bed, the total peak power would get divided by the number of zones to yield peak power per zone (watts/zone). It seems to me thaby TC - General
I'm interested in working on an ARM based design as a collaborative effort. I'm an Electrical Engineer actively involved embedded ARM development and am very comfortable with the type of electronics in Mendel. I'd be happy to help in anyway I can. TCby TC - Controllers
Here's another calculator. You can enter current, length, oz/in, temperature rise, etc. and it calculates trace width, resistance, voltage drop and power dissipation. The temperature range is limited however. TCby TC - General
rocket_scientist (Mike)... Cool! Thanks for doing that feasibility analysis. I walked through the resistance calculations and I agree with your numbers. As a double check I filled your numbers into this calculator: I got 5.75 ohms at 25 degrees C and 10.1 ohms at 220 degrees C. I have to admit that it is hard for me to conceptualize fitting 77 inches of etch in a 1 square inch area. It is alby TC - General
Thanks for clarifying James. I definitely didn't get your point before, but do now (and I agree). I don't have a RepRap yet (still learning) and so I'm a long way off from experimenting with any of these ideas. I'll probably build a vanilla machine to start with just to get something working. But I expect a heated bed will be among one of the first modifications I'll want to try. TCby TC - General
Certainly, any "solution" should be compared with alternatives. However, I don't think a PWM modulated current source, a differential OpAmp, and an A/D converter is very complex to construct. Sure, careful analysis for the PCB serpentine etch approach is required, but construction "could be" relatively simple. Simple construction is the thing that interests me about this approach. On the otherby TC - General
aka47 - good observation re: aluminum. I'm going to think about that! TCby TC - General
RE: A/D resolution check out this article about improving A/D resolution using a "running average filter". Have you figured out that you can achieve a resistance as high as 5-6 ohms using serpentine etch? I was thinking that the approach would be to have a fixed current source that can be pulse-width modulated to control temperature. Measure the voltage across the resitance at a fixed currenby TC - General
We have such a machine at work. The machine vendor won't disclose the type of plastic used for support material. It is fairly brittle and not too difficult to break away from the printed part (which is ABS). TCby TC - General Mendel Topics
Mike, I think you'll find these various articles/documents/etc. of interest. I haven't sat down and carefully gone through these yet but I got the impression after an initial read that it may be possible to measure temperature of PCB etch without adding thermistors, particularly if you can make and store reference measurements at a known temperature (i.e. 25 degrees C) for each etch segmeby TC - General
I've researched a few... and they were all Nylon. Here's one such link... TCby TC - Polymer Working Group