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short circuit :/

Discussion in 'Electronic Basics' started by Jan Nielsen, May 11, 2007.

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  1. Jan Nielsen

    Jan Nielsen Guest


    I made a circuit for a simple serial temperature system, it worked on
    the breadboard, but something has gone wrong since.

    Before I apply power to the board I have 4.3V (3xAA), when I apply power
    the voltage drops to 2.5 and keeps dropping, I added a LED to see if it
    worked, and it dosent.
    -So im guessing its a short circuit right ?

    The "diagram" is here
    The green connections is made with jumpwire, the board is standard
    single side that I etched.
    The custom components are a jackconnector (bottom right), and just
    3holes for a LM35 (VDC+, Output, GND), the 4dot is not used for components.
    The IC is a picaxe 08-m.

    I have tested the connections from the jack (bottom right) and they look
    ok, however several places in the circuit where traces shouldnt be
    connected together I get 5MOhm+ instead of a O.L. on my meter, is this
    ok ? VDC+ to VDC- gives 11MOhm in disconnected state.

    I checked the solder and traces and it looks ok, is there some mistake
    in my diagram ?

  2. You keep that shit up
    and some sort of Black Hole
    will become your Solder Sucker!
  3. Jan Nielsen

    Jan Nielsen Guest

    Rev. 11D Meow! skrev:
    Thats very helpful, thanks.
    Oh and topposting is wrong.
  4. Chris

    Chris Guest

    Hi, Jan. First off, test the batteries -- 4.3V sounds a little low,
    and suspicious.

    If you've got a 100 ohm resistor around, try placing that across the
    batteries, then measuring the voltage (anything up to 220 ohms will
    work here, too). You should be getting a pull of 45mA (less for
    higher ohms), a good load for AA batteries. Your battery voltage
    shouldn't drop by more than a tenth of a volt. If it drops more, get
    some fresh batteries and try again.

    I wouldn't worry too much about high meg ohm readings as far as
    finding a short. You did well in checking the unpowered resistance
    from V+ to COM. Double check to make sure you haven't tied competing
    outputs together, but it sounds like you've got that end covered. You
    might want to put a cheapie DMM on your long list of things to buy.

    One of the harder parts for hobbyists is the experience. You have to
    buy it one "D'oh!" at a time. If it turns out to be the power source,
    just keep it in mind next time.

    Good luck
  5. Jan Nielsen

    Jan Nielsen Guest

    Hi, Jan. First off, test the batteries -- 4.3V sounds a little low,
    I changed to 3new and got 4.7-4.8 without load.
    Found the high ohm resistance was coming from a sensor, but it is ok.
    I have a somewhat expensive DMM that works fine, well except for ampere,
    luckily thats just a fuse.

    In the end it turned out to be a mixup in my drawing and mirroring for
    the solder side, its working now.

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