Running Message Circuit

Discussion in 'General Electronics Chat' started by wdkh68, Mar 2, 2010.

  1. wdkh68

    Thread Starter New Member

    Jan 12, 2010
    29
    0
    Hi - I have a circuit which uses a NE555 & a CD4017B to drive a lot of LED's (through 2N3053's) in a running message display. The circuit requires 9V. - my question is, I'm planning on using a plug-in AC to DC unregulated wall adaptor and a LM7809. Do I need a filter cap across the LM between the output & Gnd. & if so, what value? Also, is a 12V wall adaptor ok? Thanks for your help!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Got any idea what kind of current this takes? It's really more important than the voltage.

    Perhaps you could post up the schematic.
     
  3. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Usually a cap is required, see the spec sheet for the regulator. A 12 v wall wart is ok if it is 12 volts, but the specs are not tight. You might try it and see what happens under load, even better with a scope. If you do not have the adapter look hard at the specifications.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Minimum filter cap specifications for the 78xx and 79xx regulators is an 0.33uF cap from input terminal to ground, and a 0.1uF cap from output to ground. If you don't have these caps in place, the regulator may oscillate at high frequencies.

    I suggest adding another larger cap across the input/ground of the regulator. If your input is 12v @ 1A, a 2,200uF electrolytic cap rated for 25v or higher would probably be sufficient.

    I have a couple of 7805 regulators that will oscillate in the 3MHz to 8MHz range with no caps; adding the caps stabilizes the regulators.
     
  5. wdkh68

    Thread Starter New Member

    Jan 12, 2010
    29
    0
    Help - I have a problem. I drew the schematic with Eagle and I can't seem to copy it so I can post it. I tried copy/post with Windows, but it will not copy - any suggestions? Also, Save As will only save to Eagle. Thanks!
    Sgt. Wookie - would I need both caps across Gnd. to Input? 33 & 2200?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    In Eagle, click on File, then Export... then Image
    Check the Monochrome box
    Select 100 for DPI
    Click on "Browse" next to filename
    Give it a file name ending in ".png" For file type, select PNG (Portable Network Graphics).

    Yes, you should use both caps - 0.33uF right next to the regulator. The 2200uF cap can be several inches away if you'd like, but the small cap needs to be very close to the regulator - both input and output.

    You can also use a 10uF cap on the output of the regulator, in addition to the 0.1uF cap. This will help with transient response.

    The 555 timer needs to have minimum a 1uF and 0.1uF cap across it's Vcc/GND connections.

    The 4017 should have a 0.1uF cap across it's Vdd/GND/Vss connections.
     
  7. wdkh68

    Thread Starter New Member

    Jan 12, 2010
    29
    0
    Sgt. Wookie - thanks for all of your help, but when I click file - export there is no "image" to click on. My Eagle version is 3.5 so maybe this option was added after my version. The update to the new 5.7 is $420. which I don't have. Any other suggestions?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Ahh, OK - I know the problem. I'm on 4.16r2, and don't want to pay the upgrade to 5.7 either.

    Isn't 3.5 a DOS version?

    Anyway, get the schematic sized so it fills the screen, and then you can do a screen print (Ctrl+PrtScreen or Alt+PrtScreen).
    Start MS Paint, and paste the image buffer into it using Ctrl+V or Edit/Paste.
    Crop to suit.
    Save as a .png file.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you don't have MS Paint, just upload/attach the .sch file, and I'll export it for you.
     
  10. wdkh68

    Thread Starter New Member

    Jan 12, 2010
    29
    0
    Isn't 3.5 a DOS version? No - it's Windows 95/NT. I will try your new suggestion.
     
  11. wdkh68

    Thread Starter New Member

    Jan 12, 2010
    29
    0
    I'm having an awful day - I have MS Office, but not Paint and I can't seem to find how to upload the file because it only resides in Eagle. [​IMG]
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Bummer.

    If you have the .sch file open, you could do a File/Save As...
    and that would show you the directory tree where the Eagle files are stored.

    Usually something like:
    C\Program Files\Eagle-3.5vxx\Projects\yourprojectname\yourschematic.sch

    You can usually start Paint by clicking Start/Run, and typing in mspaint.exe
    mspaint.exe is usually in the c\Windows\System32 folder.
     
    Last edited: Mar 3, 2010
  13. wdkh68

    Thread Starter New Member

    Jan 12, 2010
    29
    0
    I did get the mspaint to appear, but I was unable to do a print screen - I don't know what the problem is and I am just going to use your suggestions for adding caps and do a breadboard and see how it works. I downloaded the 5.7 light version and WOW - what a beautiful library it has. Thanks again for you help Sgt. I'm going to quit for the day.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you didn't make the library yourself - beware!

    I've found a number of errors in libraries I've downloaded from Cadsoft and a couple other sites. The errors can be expensive if you are buying PCBs from a board house, and simply annoying/time consuming if you're making the board yourself.
     
  15. wdkh68

    Thread Starter New Member

    Jan 12, 2010
    29
    0
    Thanks for the heads-up! I have been using the libraries of CadSoft for everything! When I do a ERC, it was giving me errors and warnings that I know was not true.
     
Loading...