Circuit works on breadboard but not PCB

Discussion in 'The Projects Forum' started by juve786, Jul 13, 2010.

  1. juve786

    Thread Starter Member

    Jul 13, 2010
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    Hi, I made a microphone circuit using the schematic:Electronics Projects For Dummies Parabolic Microphone and was successful and fun on a breadboard. I then wanted to make this smaller - i.e. on a PCB but i had no luck. I had my college etch a board for me which i checked was ok, but he circuit didnt work, and then I recreated the design on a matrixboard joined with copper tracks.

    What could be the issue? I tooked the components apart and recreated them on a breadboard and it works fine again :confused::(

    Also, regarding the copper track i use (it is copper tape) - how do I join the tracks? the adhesive is acrlyic and non conudcive and i have to join them by painting some leitsilber l100 over it and its very annoying:mad:

    thanks!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    You used the same components on the breadboard that were removed from the PCB?
    In that case, the parts are good, but either the soldering was not good or the PCB design was not correct.

    Without seeing the PCB, it will be impossible to say what the actual problem was.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I've soldered to copper tape many times..

    As to why it doesn't work on a PCB and does on a breadboard..Are you sure the PCB has the correct traces/connections,etc... What doesn't work about it?
     
  4. juve786

    Thread Starter Member

    Jul 13, 2010
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    Yes i used the same components on every attempt - i even replaced the lm386n-1 to make sure it wasnt that - same problem.

    I checked the connections with a continuity tester on my multimeter and it all seemed to be fine.

    I will try putting up both my pcb track designs (made by circuit wizard)

    *** edit ***
    heres my PCB track
     
    Last edited: Jul 13, 2010
  5. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Any chance of posting the picture of the PCB directly to the forum. I can not access external picture sites from here at work.

    One thought that crossed my mind that occurs a lot. Did you remember the power pins on the ICs. Some schematic programs hide these and you can forget to connect them.
     
  6. juve786

    Thread Starter Member

    Jul 13, 2010
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    [​IMG]

    Yes all the pins are connected as they should be:)
     
  7. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    There is one fault I can see but not sure if it will cause a problem. C2 is reversed on the PCB. You have the + side going to pin 8 but on the schematic the + side goes to pin 1.
     
  8. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Also just noticed C4 is reversed as well.

    Retract that last one. Just the way the board is laid out. But C2 is still wrong.
     
  9. juve786

    Thread Starter Member

    Jul 13, 2010
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    OH wow...
    even though thats true im pretty sure i paced the compoents properly but who am i to say that :p
    I thought the circuit was wrong so i pulled all the copper tapes off the board so i could reuse it for something else, but ill do it again and carfully place the components this time and let you know how it goes.
    Do the tracks seem OK though?
    thanks a lot btw
     
  10. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Yes. The rest seems fine.
     
  11. eblc1388

    Senior Member

    Nov 28, 2008
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    A very simple mistake in PCB making is to make the PCB with tracks as shown. Those tracks above are shown to be looking through the PCB via the component side and will not be visible physically.

    With the copper tracks of the final PCB facing you, your final PCB should show tracks that are mirror image of that shown above.

    If the copper tracks look exactly like above, you are doomed.
     
  12. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Very good point. I was about to post the same thing.
     
  13. juve786

    Thread Starter Member

    Jul 13, 2010
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    when i printed the track out i rememebered to mirror it. i can hold both components and track printouts back to back and they fit on each other as they should. thanks though. let me get out of bed and carry on recreating the track :p
     
  14. juve786

    Thread Starter Member

    Jul 13, 2010
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    SUCCESS!
    I guess i was stupid enough to miss out that backwards capacitor after all. At least i know i cant trust circuit wizard all too much :p

    Thank you all SO SO much for all the time and help youve given.
    Wish you all the best!
    :D:D:D:D
     
  15. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Its also a good plus for non polarised capacitors. I try to use them where ever I can. Sometimes you can't but the majority of time you can.
     
  16. juve786

    Thread Starter Member

    Jul 13, 2010
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    im a bit new to all of this, which is why i only make projects that i find rather than design my own (im only 18 and hope to start an electronics eng. degree this coming academic year)
    but despite that i clearly love my subject and enjoy learning ahead.
    what difference does a polarised cap make? and how is their use over a non-polarised decided?
    i just know basics how they store charge, time constant, only ac currents can pass etc etc.. but id go to say i no practically nothing atm :p
     
  17. tom66

    Senior Member

    May 9, 2009
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    Polarity of a capacitor generally only affects its lifespan. Electrolytic capacitors are designed so that they only work one way round... and they can catastrophically fail if they are reversed. That means they can explode, leak, and sometimes catch fire especially for tantalum capacitors. I don't quite remember the reason, but it's more expensive to make non-polar electrolytics, and it makes them bigger in size. In most cases polarity is not an issue, because electrolytics are often used to filter DC voltages and not much else. They have some applications in timing circuits and in a.c. coupling applications too, but their imperfect behaviour (e.g. dielectric absorption, polarity) makes them perform poorly.

    Have a look here:
    http://www.youtube.com/watch?v=akCI_Hm9iE0
     
  18. juve786

    Thread Starter Member

    Jul 13, 2010
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    oh ok, that helped a bit. So i guess i was lucky my circuit only needs 6V and i didnt leave it on too long when i most likely had that cap backwards :p
    thanks a lot guys!
    now to remove the hissing in the background! any suggestions? or is that inevitable with audio circuits as simple as this?
     
  19. dsp_redux

    Active Member

    Apr 11, 2009
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    A ground plane could help. Also, don't use polarized caps on your signal. Film caps is what you need. Polarized caps are used mainly for decoupling and filtering ripples on DC power supplies.
     
  20. juve786

    Thread Starter Member

    Jul 13, 2010
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    A what? :confused:
    i see its an antenna of some sort... never heard of it though:rolleyes:
    (haven't gotten onto learning about wireless yet)
     
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