Seven segment display limiting resistors

Discussion in 'General Electronics Chat' started by yuanshikai, May 23, 2013.

  1. yuanshikai

    Thread Starter Member

    Sep 17, 2011
    49
    0
    I understand the need for leds, when connected to output pins of microcontrollers, to have limiting resistors to reduce the current to an allowable level but i have a question regarding seven segment displays. I have attached 2 images.

    The first one is the common configuration for the limiting resistors - one resistor at each output pin. The second one is my question. Is that set-up safe for the microcontroller? Please explain your answers. Thanks.
     
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  2. n1spx

    New Member

    Sep 23, 2010
    4
    1
    It is safe, depending on the current limit of the display. However, the brightness of the digit will vary based on how many segments are turned on, since the current is spread between them.
     
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  3. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    The second method is possible, but you will have a problem. The resistor's value is calculated for 1 LED segment. when 2 segments are lit, half the current goes to each LED. The LEDs are not as bright. When all segments are lit, you get a very dim display. Use a network of resistors, it is easier to wire in.
     
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  4. yuanshikai

    Thread Starter Member

    Sep 17, 2011
    49
    0
    I get it now. Thanks.
     
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