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    #1

    add-on capacitance meter circuit

    Hi all,

    First post on here.
    I want to build a simple capacitance meter that I can use with my DMM. It doesn't need to have ultra 'lab' accuracy as it will mostly be used for measuring caps for use in speaker crossover circuits and very occasional, general use.
    Most of the circuits I have seen on the 'net are either too complex (and costly) PIC based or don't have the range I need. Some years ago I built an LC circuit that covers the lower ranges up to 2uF so really I would like build something to measure from 2uf to (say) 100uF.

    I would be grateful for any ideas or suggestions.


    Dave(UK)
    Last edited by oldnwrinkly; 04-22-2011, 09:30 AM. Reason: typo
    Tags: None
    #2
    Re: add-on capacitance meter circuit

    I built a kitset from Electronics Australia which did just this (plugs into the resistance range) - also quite simple (just one 4000 series IC) and a few components.

    Main problem was, I was never able to figure out the working of it (probably didn't help I was just a kid at the time)

    If you want I could scan and upload the booklet, the parts should all be easily obtainable, and I doubt EA will care since they don't exist anymore...

    It probably works just fine if you're not 10 years old!


    Another option could be this one I saw someone recently post on the forum: http://kripton2035.free.fr/digital%2...o-russian.html

    Looks quite good, and it does ESR as well, doesn't look too expensive, and appears to do a lot more than 100uf!
    "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
    -David VanHorn

    Comment

      #3
      Re: add-on capacitance meter circuit

      Thanks for the reply.

      I cannot find any info on the Electronics Australia kit online. If you have the time to send it in a PM, I would be interested in having a look at the circuit diagram.

      Dave.

      Comment

        #4
        Re: add-on capacitance meter circuit

        No problem, I'll get it tomorrow for you. Too late at night right now to do anything.
        "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
        -David VanHorn

        Comment

          #5
          Re: add-on capacitance meter circuit

          Sorry I didn't get it sooner but here it is (couldn't remember where I'd put it!)

          I'll upload the files here in case anyone else wants to give it a try too.

          Hopefully it would work better for you than it did for me. Maybe I did something wrong with mine, who knows? I may try to get it working some day...


          Since the forum resizes the images, I've put the originals in a multi-part RAR archive.

          If you need any more help just ask!
          Attached Files
          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
          -David VanHorn

          Comment

            #6
            Re: add-on capacitance meter circuit

            Many thanks for posting the documents.

            I've just skimmed through the article and, on paper, it looks to be ideal for my purpose. I'll gather up the bits and pieces (not sure if I have a 74HC132 to hand at the moment) and give it a go ASAP.
            Oh, and thanks for the rar. files - I'll print off a copy.


            Dave.

            Comment

              #7
              Re: add-on capacitance meter circuit

              The 74HC132 (ha! and I said 4000 series) should be easy to get, But you might have a bit of fun with the MOSFET though...

              I couldn't see them on RS-Components or Farnell, but maybe you will have more luck - or know of a substitute.

              Failing that, eBay has them, or since Jaycar here does, I could send you one if you have no other option.


              It looked ideal for my purposes too but as I said I never figured out how to get it working, so I can't comment on it much. That said, I am tempted to give it another try...
              "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
              -David VanHorn

              Comment

                #8
                Re: add-on capacitance meter circuit

                Well, I just tried it today and it does look as if it actually works! (and appears the bad impression of it I had previously was only due to my own misunderstanding)

                However, the socket to hold Cx isn't great so if you bump it the reading goes haywire and you have to wait for it to stabilize (as best it can, with the capacitor I tested I got a reading that constantly fluctuated between around 1.25 MOhm and 1.26 MOhm) - that would translate to about 120,000 pF or 0.12uF

                I think a better (tighter) socket for holding the capacitor would make this thing quite a useful little device...
                "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                -David VanHorn

                Comment

                  #9
                  Re: add-on capacitance meter circuit

                  It will be a while before I can get around to trying it but, when I do, I plan on using one of those spring loaded speaker terminals for holding 'Cx' - the kind you find on low end, cheap speakers where you push in a button, insert the wire and release the button to grip the wire. This should provide a more positive connection and has the advantage of being colour coded also.

                  Comment

                    #10
                    Re: add-on capacitance meter circuit

                    That sounds like a pretty good idea actually... I was thinking something like just a blade terminal (?) as I have seen on retail capacitance meters but your idea sounds good too.

                    Just make sure you have it as close as possible to the PCB to avoid adding too much stray capacitance I guess.
                    "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                    -David VanHorn

                    Comment

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