Building My 2nd DRO, Need Some Help(Intro Post)

Discussion in 'The Projects Forum' started by a._grofield, Aug 7, 2013.

  1. a._grofield

    Thread Starter New Member

    Aug 7, 2013
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    I started out with machining as a hobby and it is now my business.

    I wanted a digital readout but money is tight. So I decided to look into DIY.

    I bought built a DRO-350 kit and I managed not to let the smoke out. I'm pleased with it.

    A friend I made in China gave me his schematic and PCB files for a DRO which is much more advanced than a DRO 350.

    The biggest difference for me to get started building, is that (1) I need to order a couple sets of PCB's with which to build them (2) I have to figure out what the Altium Bill of Materials is telling me to order

    My training is in economics and then self taught machinist.

    When I was a boy and a teenager I made simple electronics from boards and parts from the Shack, but I have not done that in years.

    The DRO 350 was much easier to complete for a novice such as myself because of the huge amount of literature about completion, and the Bill of Materials was explicitly laid out.

    I have a BOM generated by Altium for this new project, but it is not so explicit. My friend in China and I have a bit of a language barrier, and he is in graduate school and doesn't have time for hand holding.

    I thought I would ask my questions here:

    Item 1 on the BOM is: 0.01uF CAPC2512L, which is a chip capacitor rated at .01uF, and according to Altium the chip's data is:
    Description Chip Capacitor, Body 2.54x1.27mm, IPC High Density Height 1.66mm Dimension 3.75mm x 1.75mm Number of Pads 2 Number of Primitives 14
    This DRO uses a power pack of 5v, and it will interface to scales that run off of 3v batteries.

    How do I figure out what chip capacitor to order ?

    I am reading as much as I can, and I keep working on my soldering skills, but a lot of this is still foreign to me. As an old dog in his 30's, it is difficult to learn new tricks.

    If I post my entire BOM, could someone help me determine what specific parts I need ?

    Thank you.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,437
    3,360
    I would approach the problem differently.

    Each component is different. Take a capacitor for example.

    First I take the nominal value of 0.01μF.
    Then I specify the maximum operating voltage.
    I know from many years of experience the capcitance tolerance, voltage tolerance and the material of capacitor to use.
    Next I select the package size of the component.

    Then I shop around for what is available at the best price/quantity.
    Many times the exact component is not available and one has to make substitutions. Again, experience counts.

    Resistors and capacitors come in standard sizes. Hence this is not usually a problem. Selecting a larger component such as a 1000μF/16V electrolytic would be different. The style and size of package would be critical in the PCB layout process.

    At this point I inform the CAD program the component and package/size to select. It is not the other way around as you have described.

    In this case, SMD resistors and capacitors sizes are simple to select. In my case I simply specify 0805 sizes, regardless of all the other parameters. The PCB layout does not care about the actual component values.
     
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  3. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    There is a list of common sizes here:
    http://en.wikipedia.org/wiki/Surface-mount_device
    Your one isn't on the list but this will be the metric size CAPC2512L.
    An 0805 (imperial size which is how it is probably listed on your supplier website) will fit on the pads without any need to change the pad size.
     
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  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,522
    2,369
    On a related note, here is one that has been around for a long time, when I used it, I did away with the transistors and went direct to the port with rotary encoders.
    It should take any quadrature encoder signal that scales often have?
    http://lindsayengraving.com/other_interests/dro.html
    Usuall not fussy as to the PC.
    Max.
     
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  5. a._grofield

    Thread Starter New Member

    Aug 7, 2013
    6
    0
    Thank you all so much for your input and time.

    I've gotten another basic EE book and I am reading it along with a guide for people who want to hack, make, and modify electronics.

    That is helping me to approach the problem as has been suggested by those who were kind enough to reply to my thread.

    I tried Mr. Lindsay's when I first got started but I could not get consistent accuracy and the old IBM Acer/Thinkpad disliked the software and the encoders.

    I appreciate your time with these replies. I will work through my BOM and try to think about this like an EE instead of someone in purchasing.

    Thank you all.
     
  6. a._grofield

    Thread Starter New Member

    Aug 7, 2013
    6
    0
    Mr. Chips: I appreciate your advise, and that is eventually where I want to be. Right now, I don't have that kind of past experience so I feel kind of inadequate changing the PCB I've got. I know for sure it is a working DRO unit when it is done.

    It runs off the OpenDRO software loaded via USB cable, so this is something I'm very excited about.
     
  7. a._grofield

    Thread Starter New Member

    Aug 7, 2013
    6
    0
    Thank you.
     
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