PCB design

Discussion in 'Homework Help' started by Mahathi Anand, Jun 9, 2015.

  1. Mahathi Anand

    Thread Starter New Member

    Jun 3, 2015
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    Hello,

    I've been assigned a project to design a charge amplifier who's LTSPICE circuit schematic has been shown in the attachment.
    So basically in here for 100Mohm resistor, I have two 50ohm SMD resistors connected in series and 1nF capacitor is a ceramic one. The i/p capacitor and the i/p supply voltage is actually a representation for a piezo sensor.
    The +-9V supply is being provided by two 9V batteries (the cap set up helps virtual ground).
    So basically I have implemented it using breadboard but I need to design a PCB but truly speaking, I have no idea about how to design. I should be using eagle software and i cannot change the components since my college is providing them.
    And the major doubt I have is as to how Im supposed to do the virtual ground of the batteries in the PCB layout.
    Also I want to know how my sensor (which has its two terminals wired) and the output (basically Im supposed its to be a BNC-BNC cable as I need to connect it to an oscilloscope/DAC) will be connected with the PCB chargeamp.jpg
    Please help me out.

    Thank You
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    Unless I am missing something in your circuit, you do not have a virtual ground as you are you using two 9V batteries.???
    The junction of the two batteries is ground reference.

    You can buy PCB mounted BNC connectors or if the project is housed in a small box, you could use panel mounted BNC connectors.

    E
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Greetings! And welcome to AAC!

    The Projects Collection (as opposed to The Projects Forum) is for sharing completed projects.

    I've moved your post into Homework Forum, where it will draw more responses.

    Good luck with your project!
     
  4. Mahathi Anand

    Thread Starter New Member

    Jun 3, 2015
    20
    0
    That is in the schematic which doesnt show the ground... Whereas when I use the batteries in the breadboard and I have to use dual supply for the opamp, I take the positive of one and the negative of other and ground it, so as to get +-9V as output from each, right?

    And as for BNC connector thing, what do i do in the eagle schematic/PCB layout for making provision for BNC connector?
    Im really sorry but im a noob when it comes to this :/
     
  5. Mahathi Anand

    Thread Starter New Member

    Jun 3, 2015
    20
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    Thank you sir.
    My bad.
     
  6. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
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    Hi,
    Look at this image, I have added supply rail 'decoupling capacitors ' which are important for most circuits.
    E

    I do not use Eagle so I cannot advise on the BNC symbol
     
  7. Mahathi Anand

    Thread Starter New Member

    Jun 3, 2015
    20
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    Okay.. Yes... I want to know how to make this arrangement on PCB...
    Anyway thanks a lot :)
     
  8. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    PCB design is an art and cannot be learned overnight.

    You may find that you need to make a custom library and create the parts yourself (make footprints based on the datasheet). I used to use Eagle all the time before I switched to Altium. You can find some Eagle component creation tutorials on Youtube. I know that Jason Lopez ("username Atomsoft") has a great Eagle Library tutorial on his youtube channel. It will walk you through creating a new library component for the BNC connector.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,565
    2,379
    On the schematic of course, a connector does not require physical form, and for the schematic to board conversion I use the free Kicad, and it is extremely easy to either modify an existing or draw a new physical footprint for a connector from the manufacturers spec sheet, if it does not exist in the library.
    Max.
     
  10. JohnInTX

    Moderator

    Jun 26, 2012
    2,348
    1,029
    You can find BNC connectors in Eagle's con-coax.lbr Lots of different types and orientations. The trick is to pick one that you can cross-reference to an actual part. Some entries have actual Mfr. Part Numbers, others are more generic.
    What I usually do is find a likely candidate, copy it to a new, personal library then check / edit the dimensions as required to match an actual in-stock part. Print the layout at 1:1 and physically place the parts on the printout to see if there are any gross errors.
    As you progress, add known parts to that personal library including real part numbers and Mouser/Digikey/Farnell etc stock numbers. Your library will begin to describe your own stock of parts with easy reordering when you run out.

    To make your own library, create a folder called MyParts or something like that. Navigate to it in Eagle's control panel and click File->New->Library. A new library will be created and opened. Leave it open, return to the control panel and navigate to con-coax.lbr, click on the first device and look at the preview. Scroll down the devices (not the package diagrams) until you see a likely candidate for your new library. Right-click it and select Add To Library. The device, including any defined packages will be copied to your library, ready to examine and edit.

    As the others have said, PCB design is blends art with engineering and it takes time and experience to become proficient. This one would be a good starter project.
     
  11. panic mode

    Senior Member

    Oct 10, 2011
    1,321
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    you will need 2 million 50 Ohm resistors, not just two...
     
  12. Mahathi Anand

    Thread Starter New Member

    Jun 3, 2015
    20
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    Im sorry, typo... 2 50Mohm resistors, but thank you :)
     
  13. Mahathi Anand

    Thread Starter New Member

    Jun 3, 2015
    20
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    Oh yes, Thank you. Ill do as you've suggesed
     
  14. Mahathi Anand

    Thread Starter New Member

    Jun 3, 2015
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    Yes. Im aware of it, but I have to do it now without any experience and I have no choice.
    Thank you for the video tutorial that u have suggested, I'll check out.
     
  15. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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  16. Mahathi Anand

    Thread Starter New Member

    Jun 3, 2015
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  17. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I was wondering because your topology does not resemble either circuit in that application note.
     
  18. Mahathi Anand

    Thread Starter New Member

    Jun 3, 2015
    20
    0
    No it isnt quite but my circuit works fine. I have tested it :)
    And any normal integrator would do the job... As long as ur frequency response is as its supposed to be.
     
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