Digital Circuits and LEDs

Discussion in 'General Electronics Chat' started by Ryuk, Oct 23, 2012.

  1. Ryuk

    Thread Starter New Member

    Oct 9, 2012
    18
    0
    Let's say you have a digital circuit with a certain function that outputs the signals in a series of LEDs.

    So say I want a 1100 output. In that case, the first two LEDs would light up and the last two would be off. However, due to the laws of electricity this will not happen. This is because an LED is connected to a power source and a 1 output going into the other side of the LED would produce no potential difference and hence the LED would not light up. So for a 1 output, the light would stay off and for a 0 output, the light would turn on. This is negative logic! Up until now I have been avoiding this issue by simply placing an inverter chip between my output and LEDs. Is there another way to solve this issue?
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,364
    Yes. You can connect the LED with it's cathode to GND.
     
  3. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Depending upon the internal output circuit of your IC, you may need a pull-up resistor, ie open collector output of a gate driving the LED.
     
  4. electron_prince

    Member

    Sep 19, 2012
    93
    3
    are you using 8051 Port 0?
     
  5. Wendy

    Moderator

    Mar 24, 2008
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  6. Ryuk

    Thread Starter New Member

    Oct 9, 2012
    18
    0
    Yes, previously, I had the power, pull up resistor, and anode side on the left and the cathode side and output signals on the right.

    I switched the sides of the LEDs and connected GND to the resistor instead of power and it now works. Thanks guys.
     
  7. nkosinathizvimba

    New Member

    Aug 24, 2012
    6
    0
    The LED used will have a voltage drop, specified at the intended operating current.
     
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