short in my circuit! I must be blind

Discussion in 'General Electronics Chat' started by mikey11, Mar 21, 2008.

  1. mikey11

    Thread Starter New Member

    Mar 21, 2008
    1
    0
    Can anyone help me find a short in my circuit?

    I am making a timer for a local toastmasters club, I will be using a pic16f628a with a 16x2 hd44780 display.

    Three buttons and three LED's

    I have made my board using a 7805 to step down a 9v battery for testing purposes.

    when I measure between +5v and gnd I get 3.06k ohm resistance
    I can't figure out where I've gone wrong. when I connect the 9v battery I get a hot 7805, but I have removed quickly and I know 7805s are quite tolerant to silly mistakes.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    3,000 ohms to ground from a 5 volt regulator is only 1.6 milliamps. That won't make the 7805 get hot. Do you have a capacitor from the 7805 output to ground to bypass oscillations? If not, add a .1 uF ceramic as close to the output terminal (7805 pin 3) as you can place it.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,577
    231
    Pad at the left end of the top resistor is shorted to the top trace, or it looks like that in the image. That shorts the right and center pins of the 7805. Input to ground or output to ground, depending on orientation.

    Ken
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    KMoffett nailed it.

    Take a look at the attached edited version of your toast.JPG
    The short (from the output of the 7805 to ground) is circled in red.
     
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