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"Hello World" affecting other LEDs

Discussion in 'Microcontrollers' started by warp_kez, Sep 6, 2008.

  1. warp_kez

    warp_kez New Member

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    I have done the traditional Hello World with a blinking LED.

    When it runs, it affects the power LED by dipping it.

    I have the power LED after the 78L05 regulator with a 210ohm resistor.

    Any ideas?
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Its possible that the 78L05 reg is current limiting, you could try a 7805 reg.
    Whats the voltage source, mains or battery.?

    Also what capacitors do you have on the +5V line.?
     
    Last edited: Sep 6, 2008
  3. warp_kez

    warp_kez New Member

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    I have attached the schematic for the board.
     

    Attached Files:

  4. dave

    Dave New Member

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  5. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    You are showing a 7805 reg [1Amp] not the 78L05 [100mA].?

    You should add a 470µF cap across the +5V to 0V

    Whats the LED matrix made up of.? Rows/Cols ?

    EDIT: its also advisable to have a 100uF cap as close as possible to the MCU pins 20/10 +5v/0V
     
    Last edited: Sep 6, 2008
  6. warp_kez

    warp_kez New Member

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    I am not real good with documenting my work etc.

    I just plugged the regulator circuit into LTSpice, I think I am starting to see what the problem might be. Without the LED, I get an output of 5.2v at ~120mA. When I add the LED, voltage drops to 4.7v at ~80mA.
     
  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Which 5V regulator are you using a 78L05 or 7805 ?. and the caps I mentioned are required.
     
  8. Willbe

    Willbe New Member

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    The eye responds to peak brightness; by varying the LED duty cycle and using a big enough cap and a small enough series resistor you can probably fix this problem without dropping the perceived brightness.
     
  9. Pommie

    Pommie Well-Known Member Most Helpful Member

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    Are you sure about that because I have varied an LEDs brightness by varying the duty cycle and keeping the peak current the same.

    Mike.
     
  10. rgbphil

    rgbphil New Member

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    Hi,

    120mA sounds like a lot for a micro with two LEDs (unless I'm missing something here).

    I presume you've checked for shorts, miswiring etc?

    Other than that I'd suggest looking at the program and checking if there are peripherals enabled that shouldn't be. For example with a PIC if you have enabled analog input for a digital output you'll get a serious power drain like this, perhaps even damage the chip.

    Not sure about ATMEL. I note in your cct your LED output is connected to pin AIN0.

    Phil
     
  11. warp_kez

    warp_kez New Member

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    I have redone the schematic.

    I have checked for shorts, but nothing is obvious. I did run around with a knife to make sure, but that does not guarantee I got them all.
     

    Attached Files:

  12. warp_kez

    warp_kez New Member

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    Well, I bread boarded the original circuit, and it worked exactly as it should. I must have a short somewhere.

    But I am going to do the MkV.
     

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