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Thread: what to do with this 3+ axis dental cnc machine

  1. #37
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    Default Re: what to do with this 3+ axis dental cnc machine

    hey sorry for the delay, winter hit fast and hard here this weekend, and I was not ready. Also I bit into that soldering iron station project and ended up on some tangents, useful, but tangential nonetheless.

    Um... which SAMD21 dev board did you get?
    this one didn't put much though into it, just wanted something to try.

    Um... typo?
    yup


    great info on the opto / grounding stuff. a while back I was running stepper signals through opto's and came into some bizarre behavior, mostly when stepping fast (<500uS between steps). I began to suspect the optos were slow as they were part of my "old electronics inventory". I had 4 different kinds, most of which did not have a modern standardized format (i am sure you've seen old datasheets)....not really knowing what I was doing, and lacking a scope, it was days of reading sheets and trying to work out the math, I did eventually settle on some 4n24's i had around, I knew they were the fastest I had, but never truly knew they were fast enough. So that backstory leads me to my soldering station project. So as I was building a couple of simple power supplies and a pwm mosfet circuit, I spent some time re-familiarizing myself with using a scope (its been at least 10 years since I used one). OMG what a useful diagnostic tool! The way you felt about the microscope is how I feel about the oscilliscope. I had spent years trying to troubleshoot signals with just a multimeter and now I am staring at a WHOLE new world. And more importantly, I can SEE the results of different components. For example, I sat there and played with all sorts of combinations of resistors & caps on my voltage regulators and got to see the subtle differences they made. I learn quite well from that sort of direct feedback. They when I got to the opto that drives the mosfet, I swapped some of those other chips in & out and got to see exactly how signals were getting cut off....really cool. Tonight I would like to compare the analog out of an arduino nano (328) and the samd21. You had mentioned the method of generating analog signals is much better on the samd21, so I would like to see that.

    I am still working on this damn soldering station...only part I didn't breadboard was the thermistor circuit, as I have wire many of those....but it is an PTC(although I am starting to think its actually an RTD) and I am used to NTC. thought that would only matter in software, I can measure the resistance as I heat it and it climbs, but then I stick in a voltage divider and end up with the full voltage. I think its got to do with the size of the divider resistor, but I haven't quite zeroed in on it.


    When that is finally done, I do plan to start building a proto type axis control circuit. More generally, my 1st goal is to get 1 axis moving around with an arduino.

    Last edited by mtraven; 11-11-2019 at 11:49 PM.


  2. #38
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    Default Re: what to do with this 3+ axis dental cnc machine

    hey sorry for the delay, winter hit fast and hard here this weekend, and I was not ready.
    Eh, no problem. I've actually been a bit busy myself - but with the opposite problem: I spent the weekend driving a tractor around collecting brush & dead tree limbs & piling them in a dumpster so our place here doesn't burn down (I'm in the middle of California). I've actually got my air conditioning going as I type this. (!)

    this one didn't put much though into it, just wanted something to try.
    Hmm... funny that, I was having some weirdness with the Arduino M0 clone that I have here on Friday (although at the time I was starting to suspect it should have been called 'Fryday' - my signal generator glitched out and dumped 5v into the 3.3v-only inputs on the board; and I thought I cooked it)... so... I went on Amazon and ordered another board to test with. Thru sheer luck, I ended up with that exact model of SAMD21 board.

    Only after the new board arrived did I discover that it was just the bootloader that had gotten corrupted; and after going around a few times flashing a new bootloader and the sketch I was playing with using the Atmel-ICE it's now working without a hitch.

    Re: Scopes.
    Scopes are cool. All kinds, too... micro-, tele-, oscillo-, and even kaliedo-.

    Re: Analog out.
    The DAC on the SAMD21 is connected to Arduino pin A0. Doing an analogWrite() to any of the other pins will result in a PWM signal being generated.



  3. #39
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    Default Re: what to do with this 3+ axis dental cnc machine

    Thru sheer luck, I ended up with that exact model of SAMD21 board.
    i suspect it has more to do with amazon's search algorithms.....the real question is did you buy the soldered or un-soldered version?

    I gotta say, it calms be a bit that even someone who know what they are doing messes up a board every now and then. So when you thought you fried it, what were the symptoms? Would it just not register on USB or take a sketch upload? I ask because I have several boards that I think would work if I got a new booloader on them, but I had tried that a while back with no success. Some of those boards still run the sketch that is on it, but wont connect to take a new upload. I should probably work out the process of uploading a bootloader with a working chip so I know my setup is right..then if it doesn't work, I know the board is donzo.

    What board do you select when uploading a sketch on your clone? I have all sorts of options: arduino M0, arduino M0 pro (programming port), arduino M0 pro (native usb port), arduino Zero (programming port), arduino Zero (native usb port). I just guessed at "arduino M0 pro, native usb" and it seems to have worked.

    The DAC on the SAMD21 is connected to Arduino pin A0. Doing an analogWrite() to any of the other pins will result in a PWM signal being generated.
    so just to restate it so I make sure I understand: I can expect a different waveform using the DAC with something like analogWrite(A0, n) where as an analogWrite to any other pin will look the same as a standard arduino.

    edit: well I just checked that out on my scope side by side with a regular pin, pumping up duty every second or do...---that is REALLY cool to watch a solid line rise side by side with the pwm chopped output. its a shame there is only one though.

    still working on that soldering station, not having fun. It is an RTD, I finally got a circuit that varies voltage with temperature, but its only like 15mV variation, so I am working on amplifying that up to either 3.3 or 5v so my nano can read it...that what I am trying to work through tonight.



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what to do with this 3+ axis dental cnc machine

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what to do with this 3+ axis dental cnc machine