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Help needed desperately with PIC LCF meter

Discussion in 'General Electronics Chat' started by bigal_scorpio, May 2, 2008.

  1. kasamiko

    kasamiko Member

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    With due respect sir, if you are only interested with the L part this one is highly recommended,,,



    [​IMG]





    Here's what you can get:


    Voltage Supply: 6 - 16V
    Accuracy: 1%
    Full Automatic Ranging
    Inductance Resolution: 10nH

    Capacitance Resolution: 0.1pF


    LC Meter's Inductance Measurement Ranges:
    - 10nH - 1000nH
    - 1uH - 1000uH
    - 1mH - 100mH

    LC Meter's Capacitance Measurement Ranges:
    - 0.1pF - 1000pF
    - 1nF - 900nF


    I personally built this one....and it works flawlessly for the first time you applied power in it...:)


    BR
     

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    Last edited: Mar 26, 2011
  2. lynx

    lynx Member

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    hello...

    no unfortunately i'm not...but that doesn't mean it's impossible to send it over
    to you :)


    you think it's tough we solve here?..


    Hi

    thank you too for your support, but i prefer to troubleshoot the one i already have :)
     
    Last edited: Mar 27, 2011
  3. bangash102

    bangash102 New Member

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    ac to ac converter.

    hi every body ..i want to operate at 220VAC to 2230VAC .ant want to shut down my system when voltages goes high from 230 VAC ...can anybody help me ???
     
  4. dave

    Dave New Member

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  5. lynx

    lynx Member

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    hi...

    i have no news from you... do you think it's hard we troubleshoot it here?!
     
  6. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Looking at your PCB layouts, I would say the circuit should work.??

    I will take another look in case I have missed something.
     
  7. lynx

    lynx Member

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    Hi ericgibbs

    that's exactly the reason that i asked for help from this thread here...

    the problem is rather peculiar and i can't figure out what can go so wrong..
    the circuit only has few resistors few capacitors and a PIC.

    i thought it could be the crystal...but the PIC and the display starts..
    i was thinking it might be the 4011 so i changed the TI CD4011 with a HEF4011BP

    the author says the following:

    These are the results of my findings when using different makes of 4011 in the LCF Meter when in Capacitance mode:

    HEF4011BP no problems
    HCF4011BE parasitic oscillation at about 6MHz
    MC14011BCP parasitic oscillation at about 2MHz
    RS4011B parasitic oscillation at about 4MHz


    but there's no improvements since the above refer to
    capacitance mode...

    recently a friend of mine suggested i should return the instrument
    to it's previous state...meaning i should put back together the rotary
    switch because the problem might have to do with stray capacitance
    and inductance.

    but i don't think such thing might be the problem...
     
    Last edited: Mar 31, 2011
  8. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi lynx,
    Do you have a scope.? this would check for any unexpected oscillations in the build.

    The other check you can do is to connect a signal generator to the FREQ input pin, set for TTL levels, set the sig gen for 10KHz and watch the LCD for this 'drift' in frequency.
    If the displayed frequency is stable that will prove that the PIC/xtal etc is OK.

    Also connect the TEST leads that normally go to the 'inductor' under test together, ie: short them together, monitor the displayed value on the LCD.

    NOTE: any unused gate inputs on the 4011 should be connected to 0V or +V. [choose 0V or +V to get the state of the required output from the gate, high or low]
     
  9. kasamiko

    kasamiko Member

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    yes! I got the 3.2768MHz crystal...:D
     
  10. lynx

    lynx Member

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    hi

    i was away for awhile, so eric.. using a 500Hz/5V square signal, the LCF
    shows exactly and steady 500Hz/6.3H currenty i can't test it with another
    frequency.

    does that prove that the PIC and the crystal is OK?
     
  11. kasamiko

    kasamiko Member

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    can somebody re upload the latest full working schematic and pcb layout including all the mods..

    TIA
     
  12. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    From that result, I would say the program/PIC is running OK.
    The fault must be on the pcb layout or a defective component.
     
  13. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Hi
    Are you asking for the details of the OP's version of the LCF meter.?
     

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  14. lynx

    lynx Member

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    Hello eric :)

    what can possibly go so wrong? i have already changed a couple of time the 4011 gates..
    you have already seen the PCB from both sides and both you and me we can't notice any
    defect...

    can that be a leaky capacitor?! ceramics don't fail so easily...


    P.S after the mod you told me to do..can you also tell me which resistors and capacitors
    aren't needed so i can take them out?

    thanks!
     
    Last edited: Apr 26, 2011
  15. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi lynx,
    As you know each section of the L and C part of the measurement logics oscillates as expected is simulation.

    When I modified the PIC program for 'AL' the OP of this thread, I actually built the logic on a breadboard in order to check the program mods.
    It worked OK.

    I will rebuild only the Inductor section and program a 16F628A with the modified 628A program, see if I can find the problem,,, if it exists.

    Let you know, give me a day or so.
     
  16. lynx

    lynx Member

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    sure eric... :)

    meanwhile do you think i sould check anything else?
    or the conclussion from the frequancy measurement is enough?
     
  17. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    The program calculates the Cap and Inductor values by measuring the frequency they produce when they are part of the oscillator circuit.

    When you put in your test frequency of 500Hz the reading remained steady which suggests to me the program is measuring the freq OK.

    Do you have access to a frequency counter meter,? if yes, you could check the output stability of the inductor section oscillator,
     
  18. lynx

    lynx Member

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    yes.. i have a multmeter that can measure frequency, but i don't know how high
    it can go, which pins you want me to try to measure and what results i should
    expect?
     
  19. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Use an inductor that will give a frequency in the range of your DFM.
    When its running measure the pin on the PIC where the 'frequency' from the 4011 is connected, it should remain fairly stable over a few minutes as you keep checking it.
    If it dosn't then the problem thats causing the drift in the inductor measurement is on the pcb and not in the PIC, you have already checked the PIC program when you injected that 500Hz signal.
     
  20. kasamiko

    kasamiko Member

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    Thanks! got the hard to find xtal..I'll give this a shot...:D

    I stumbled upod this promising statement..

    is this true??

    :D
     
    Last edited: Apr 27, 2011
  21. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi lynx,
    I assume that on your version of the LCF meter that you have the SET push button connected.? and that you carry out the Correction procedure as explained in the pdf.?

    I have built the inductor osc section and it works OK, testing using a number of 4011 gave wide differences in the base frequency [ ie: when the test probes are shorted together]
    The 10Kpot has a VERY wide range of frequency settings, I guess thats why the SET push button is used before measuring.

    The base 4011's frequency outputs remain stable enough, over many tens of minutes.
     
    Last edited: Apr 27, 2011

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