How to interpret ceramic disc capacitor labels

Discussion in 'General Electronics Chat' started by mtericJL7, Dec 31, 2007.

  1. mtericJL7

    Thread Starter New Member

    Dec 31, 2007
    4
    0
    I recently purchased an assorted bag of ceramic disc capacitors from radio shack. I need some guidance in interpreting the labels. I understand that the first two numbers are the significant figures and the third (if present) is the number of zeros to be annexed to the first two numbers which then is the rating in picofarads, however, my question has to do with how some of the capacitors have there numerical labels underlined and others do not. I have a picture of these capacitors if anyone needs to see it. I could Really use a good pdf tutorial on this. Your help will be very much appreciated as I am attempting to build my first electronic project: and audio amplifier with the LM386N analog IC.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Here's a great resource page for you:
    http://educypedia.karadimov.info/electronics/datacomponent.htm

    In particular, have a look at this page:
    http://www.marvac.com/fun/ceramic_capacitor_codes.aspx

    Ceramic disk caps aren't the best choice for audio applications; actually they're pretty bad. If you're not building a hifi set though, no worries - don't be surprised if you wind up with distortion, particularly at higher volume levels.

    Have a look at this page for a comparison of what kind of responses different types of capacitors give:
    http://members.aol.com/sbench102/caps.html

    You could always build it first with the ceramic caps on a breadboard, and then try it again later using better caps; see if you notice the difference.

    Have fun! :)
     
  3. mtericJL7

    Thread Starter New Member

    Dec 31, 2007
    4
    0
    Thank you for your help in pointing me towards some resources. I appreciate it very much. You said that ceramic disc caps are not very good for audio apps? Would it be better to use the resin dipped solid tantalum caps from Jameco or the aluminum electrolytic ones?
    I know my questions are a bit amateurish by I am fairly green at this point. I just recently went to a book store and purchased some electronics textbooks
    and some old electrical engineering hand books, treatises on eletricity and magnetism, circuits, and some trouble shooting books that show a person how to use a multimeter.I also have an interest in amateur radio and have ordered a kit for a 20 meter band receiver from Ramsey Electronics, so I was going to practice a bit on that audio amp project with the LM386N IC before I jumped on my 20 meter kit. Would I be wrong to assume that I will need and oscilloscope at some point?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The choice of capacitor depends quite a lot on application. If the ceramic caps are for bypassing voltage rails to ground, then they are a really good choice. Their internal structure makes them work better passing high frequencies than electrolytic or tantalum types. They have sloppy tolerances (usually -20%/+80%) so you usually have more capacitance than you pay for.

    On the other hand, they come in relatively small values, especially compared to electrolytics and tantalums. They can also rarely be microphonic, meaning that the creamic layers inside can jiggle a bit when mechanically vibrated. This can cause them to generate a bit of electricity (piezoelectricity), which messes with the circuit they are in.

    On supply rails it is conventional to use electrolytics to filter DC ripple, with a ceramic cap in parallel for bypassing high frequencies. Capacitors used for coupling signals are usually film types, like polypropylene or polyester.

    An oscilloscope is the tool for audio and radio work. They are very expensive, especially if they have the bandwidth for radio work. You might want to hunt around for a secondhand o'scope. You can find companies online that sell reconditioned ones. Some commentary I have seen indicates that buying one on Ebay is pretty iffy as to the actual condition of the instrument.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Before you dive into building your 20-meter kit, it would be a good idea to practice on several relatively inexpensive kits.

    Get a good soldering iron, preferably with a temperature-controlled tip. Don't scrimp here. A good iron will be a pleasure to use.

    Use SN63/Pb37 solder. It has a relatively low melting point and is "eutectic", meaning that it goes directly from a liquid to solid state, minimizing the chance for a "cold" or crystalline joint. Cold joints happen when the components are moved when the solder is in a "plastic" state. They're weak in strength and are high in resistance.

    Clean your connections before soldering using a small brush and the purest isopropyl alcohol you can find. Isopropyl alcohol readily absorbs moisture from the atmosphere, so keep it covered. It also burns with a flame that's very hard to see, so keep your work area free of ignition sources. If your components' leads are not "bright", they're corroded and need cleaning. Scotch-brite (tm) pads work very well for that; they'll strip off the corrosion without removing the still-good tin plating.

    An O'scope is extremely handy for troubleshooting. I picked up a couple of O'scopes from E-bay that had problems, one of which I knew of beforehand. One of the problems with older O'scopes is that the electrolytic capacitors usually need to be replaced. Newer O'scopes are practically impossible to fix because the guts are proprietary.
     
  6. mtericJL7

    Thread Starter New Member

    Dec 31, 2007
    4
    0
    Thanks guys. I wish I had something to offer in return for your words of advice. I really appreciate you guys taking the time to help a novice out with some pointers. I'm sure to be back in the near future asking some more amateur questions. Hey by the way, I attended my first Union meeting for Sheet Metal Workers Union Local 66 in Kirkland Washington. I took the oath and was Sworn in and even got to vote on a pension. The debate was kind of heated but the rules of order were obeyed for the most part. Needless to say, it was a very cool experience. I felt very welcomed after taking the oath. You'll have to forgive me I'm just a little excited. Take it easy bros.I'm going to bed, I gotta work in the morning.Peace.
     
Loading...