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Help needed desperately with PIC LCF meter

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

  1. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Eric,

    You've done it again, may have to start calling you sherlock! ;)

    The resistor fix makes my meter work without locking with either Pic in!

    Maybe now Bob can build his meter.

    All the best............Al :)
     
  2. mrx23

    mrx23 New Member

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    Great work Eric!

    I will definitely start building the meter:)

    And one more thing. Is it possible to divide the incoming Ext. Freq. source by 2 (or more) with HW. And then give a gain of 2 (or more) in SW (just for the Ext. Freq subroutine)?
    So it will able to measure freq up to 10Mhz (maybe 20Mhz) instead of 5Mhz.

    What would you recommends for isolating the external signal at this frequency. It would be great to measure +- signals (like freq. generator's).

    Thnx!
    Bob
     
  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Hi Bob,
    If I was going to use a predivider for the external freq input I would chose 'divide by 10'.
    In that way it would be easier to read the displayed value...
    At the higher freq you are not going to get the higher accuracy, so div by 10 makes more sense to me.
    Also the PIC could handle the divided freq.

    If you want to measure standard TTL logic levels the HCT or F series of divide by 10 would be OK.

    For lower level signals a wide band preamp before the divider would be OK.

    Does this help.?
     
    Last edited: Jun 3, 2008
  4. dave

    Dave New Member

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  5. mrx23

    mrx23 New Member

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    Here is a cool Freq meter up to 50Mhz with the old 16F84.
    We could use the input stage (or a simpler one).
    A Low-Cost 50MHz Frequency Meter

    LCF meter can measure 5Mhz TTL signal accurately.
    So the final precision will depend on the preprocessing of the input signal.

    I would like to measure sine/triangle/square signals from the Signal generator (and other sources). The signals are about +-2V range.
    So we have to make it half wave (GND to +2V), buffer (or amplify), feed into Schmitt trigger, and divide the TTL output as much as we want, then feed the PIC with it.

    Does this LCF support auto-ranging function? (Hz,Khz,Mhz)
     
  6. mvs sarma

    mvs sarma Well-Known Member

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    It would be very difficult to procure chips like MC10116 (ECL types). thus it is preferable not to venture.

    It is just a frequency meter. if such meter is needed with 9 level offsets as some HAMs use , One may find at www.hamradio.in and it used 16F628 , an improved version over 16F84 replacement for F84. I have a working version of this design.


    Also I made a counter using the design by Fransesco Morgantini (ik3oil) and it works fine. Thanks to Morgantini.
     
  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Hi Bob,
    You should decide whether you want a simple LCF meter or a good quality freq counter.:)

    I would suggest you build both units, look at Sarma's link.
     
  8. mrx23

    mrx23 New Member

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    Ok, 5Mhz will be fine. But the bipolar input would be very great.
    Is this can achieved with the anti-parallel diodes?
    http://www.hamradio.in/circuits/images/lcdcntr.gif

    We will need an external Schmitt Trigger, because there is an another signal source on the RB6.

    What Schmitt Trigger should I use, and what will be the trigger voltage?
     
  9. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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  10. Kryten

    Kryten New Member

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    Is it possible to extend it to measure frequenz as well without much alterations (I see that there are a couple of poles free on the rotary swithc).

    I know threr will be a som mods to both the schematic as well as the software, but has anyone thought about doing so?
    Im thinking about the PIC LCF meter that the thread is about
     
    Last edited: Jun 19, 2008
  11. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    It already can measure and display a frequency, use the 'ext' input.
     
  12. tariq7868

    tariq7868 New Member

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    HI bigal_scorpio,
    i m thinking of building the lcf meter from the epe mag of feb 2004 .. but i came to know there was some error in measuring the some capacitances and i have got here the circuit diag of it ,, so can u plz tell me whether u used the same circuit in the pdf i have attached.????
     

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  13. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    While Al is offline, I will answer, it is the circuit that he built.:)

    What is the error regarding capacitance measurement.?
     
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  14. blueroomelectronics

    blueroomelectronics Well-Known Member

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  15. tariq7868

    tariq7868 New Member

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    it was just that i happened to see some guys saying 'i noticed unexpected spurious oscillations in capacitor mode' & 'i cant have precision in nf scale, the capacitances of for example 10 nf became 4.7 nf' ... so thats why i thought of confirming...
    One more thing :: i (too) cant seem to find 3.2768Mzh so can i use 3.5 or 4Mhz ?
     
  16. blueroomelectronics

    blueroomelectronics Well-Known Member

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    If you change the crystal you'll have to rewrite the source code.
     
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  17. tariq7868

    tariq7868 New Member

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  18. tariq7868

    tariq7868 New Member

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    Hello.. i m also trying to build lcf meter using 16f628A but i cant download the above attached file (something wrong with the link) so can anybody plz again attach the hex file ??? thanks
     
  19. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Ive rezipped all the program files.
     

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  20. tariq7868

    tariq7868 New Member

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  21. tariq7868

    tariq7868 New Member

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    i hav made the pic lcf meter using 16f628A, but when i turned on the meter,only one line of rectangular boxes is appearing on lcd (i.e noting changed) & nothing happening.. i have checked all the connection which are alright..
    i have a doubt abt my 3.2768 crystal, which was not available and i found it by chance. the value on the crystal is written as : ECS v 3.27 - 17 ,,, ..what do u think ???
     

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