LC Meter ?

Discussion in 'General Electronics Chat' started by iamspook, Sep 6, 2008.

  1. iamspook

    Thread Starter Member

    Aug 6, 2008
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    Has anyone here built one of these?:
    http://electronics-diy.com/lc_meter.php

    I can't find the HEX code for it. I'll have a go if I can find the code
    but I don't see the point of independently programming it.

    Thanks!
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
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  3. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    Take a look at this site http://ironbark.bendigo.latrobe.edu.au/~rice/lc/ for a selection of PIC L/C meters.

    I built the "LC Meter Version 2" and it works like a dream. The only change I made was to use a low drop-out 100mA voltage regulator instead of the LM7805 and ditch the external power. Without LCD backlighting the unit only takes about 12mA so a 9 volt battery lasts for ages.
     
  4. iamspook

    Thread Starter Member

    Aug 6, 2008
    27
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    Many thanks! It's good to know that it's been built by someone other than the original. I'll have a go at this one. Were there any difficult parts? I've got a 2 x 16 LCD display already. Could I use that one?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Sure, the 2x16 LCD should work fine - if it has a 44780 controller.
    Use the recommended caps.
    You can't use the internal oscillator; yes, the 16F628 has one, but it's RC and won't be nearly accurate enough.
     
  6. iamspook

    Thread Starter Member

    Aug 6, 2008
    27
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    Thanks. Yes - it has 44780 controller.

    I've got to build a PIC programmer first :rolleyes:
     
  7. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    As the Wookie says a 2X16 LCD display is fine, in fact that's what I'm using one.

    The hex code is compiled for a PIC16F628 which is an obsolete part (you can get still them but they cost an arm and a leg) however the code does run with no modification on a PIC16F628A which is a current chip.

    Other than the old PIC everything else is a current off the shelf part and should not present any problems.
     
  8. iamspook

    Thread Starter Member

    Aug 6, 2008
    27
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    Excellent! I've got a couple of those as it happens - just to play around with originally.
     
  9. Eddy25

    New Member

    Dec 10, 2008
    1
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    Just to say as my first post in this forum, that I have also built the 16F628 based lcmeter and it's working like a dream; Yes it's very accurate since it indicated a value of 1004 pf for a standard styroflex capacitor of 1nf.
     
  10. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    I don't know what your need is, but if you're an experimenter, like me, there is no need for an LC meter. I know a cheaper way to determine L or C. If you're interested say so and I'll explain.
     
  11. steveb

    Senior Member

    Jul 3, 2008
    2,433
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    I don't know if he is interested, but I certainly am. Please explain.
     
  12. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    Hi Steve, glad to be of help. You need to make a simple parallel LC circuit which is called a tank. And you need a variable frequency signal from either a function generator or an rf signal generator and you need either a frequency counter or an oscilloscope. If you have the necessities, determining L or C is easy. The following may sound a little complicated but with practice it's a piece of cake.

    If you're looking for C, then you need to know L and if you're looking for L you need to know C. This is easily accomplished with marked capacitors. Tantalum capacitors can be quite accurate, so use one of these to determine the inductance (explained in a minute) of an inductor -- homemade or otherwise -- and now you have two known values for L and C.

    If your measuring L, put it in parallel with a known C, then input a sign wave to the tank through a 33K resistor. You won't see anything on the o scope intil you find the resonant frequency. Then it pops up. Wiggle the frequency back and forth until you're sure of the maximum voltage. This is resonant frequency.

    Now use this formula to solve for L: L=1/[(2*pi*f)^2 * C]

    Or if you are testing for capacitance use your known L and this equation:

    C=1/[2*pi*f)^2 * L]
     
    Last edited: Dec 11, 2008
  13. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    Ah, OK, just direct experiment. This is good since you can do the measurement near the intended operating frequency. Not complicated at all, if you have the equipment which is pretty standard. Ideally, you would like to have good quality reference components with precisely known values (including frequency dependence), but these can be established using the same approach with RC and RL circuits and an ohmeter for calibration.

    Thank You!
     
  14. PRS

    Well-Known Member

    Aug 24, 2008
    989
    35
    You're welcome. I'd like to add that this technique was good enough for me to make an Am radio and an Fm radio winding my own toroids and connecting capacitors in series (in lieu of variable caps). It's a seat of your pants method but it works. I've also found that transistors can be matched by making a bypassed CE amp with high input resistance (to make the circuit dependent on Beta) then comparing the gains of a tray of BJTs, and I've had good results.
     
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