16 7-segment display with PIC 16F877A

Discussion in 'Embedded Systems and Microcontrollers' started by LEOLOGIC, Jul 29, 2010.

  1. LEOLOGIC

    Thread Starter New Member

    Jul 29, 2010
    1
    0
    Hi Friends,

    I am trying to drive 16 LED CC 7-segment display with PIC 16F877A through HEF4511 BCD to 7-segment latch/decoder/driver & CD4515 4-to-16 line decoder. RB0,1,2,3 are used for 4511 and RB4,5,6,7 are used for 4515. Can some one help me because I am unable to control the flicker?

    Thanks in advance.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    You've posted in the wrong place. This should be in Embedded Systems and Microcontrollers.

    A mod will be along shortly and move it I expect.
     
  3. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    Apart from adding more hardware, I can suggest optimizing the code and making sure there is only one change on portB per digit (ie load a variable with the required output, then write that to portb.)
    If you could post code that would be helpful.
     
  4. MMcLaren

    Well-Known Member

    Feb 14, 2010
    759
    116
    May I ask if you happen to know what the display refresh rate is from your software driver? You're driving it at 1/16th duty cycle, correct?

    May I ask how you're grouping these displays, please? Is it one big 16 digit display, or two 8 digit displays, or something else?

    Mike
     
  5. Bosparra

    Member

    Feb 17, 2010
    79
    3
    I had similar issues with multiplexing only 4 displays. Playing around with the timing, I eventually settled updating each display every 15ms. But the display is very faint. I suppose it could be improved by increasing the current.

    You would have to update each digitALLOT faster, but brightness will be sacrificed, because of the low effective duty cycle supplied to each display. The best duty cycle you will be able to get is 6%. The only remedy is to increase the frequency, but with a PIC you are going to run out of clock cycles FAST.

    From where I am sitting, adding more hardware is the only solution, perhaps a dedicated micro controller to power just the display.
     
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