running leds

Discussion in 'Homework Help' started by eldadoh, May 7, 2014.

  1. eldadoh

    Thread Starter New Member

    May 2, 2014
    23
    0
    I used 3 jkff and 4-16 decoder to make 16 running leds . they work like this :
    *
    -*
    --*
    ---*
    ----*
    -----*
    ------*
    -------*
    --------*

    i want they run like :
    1
    12
    123
    1234
    12345
    123456
    1234567
    12345678

    i want to do this with shift register? can you tell me how does it work and where I need to connect the shift register .? thanks
     
    Last edited: May 7, 2014
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    Are you using a 555 timer or something similar to clock the 3 * F/F's.?

    Its is possible to use shift registers to get the sequence that you have posted, but what do want to happen next when all the LED's are lit.?
    E
     
  3. eldadoh

    Thread Starter New Member

    May 2, 2014
    23
    0
    hi I add picture of my circle .
    I want that after all the leds are on it starts again from the first led to the first+second and go on

    1
    12
    123
    1234
    12345
    123456
    1234567
    12345678
    1
    12
    123
    1234..
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    OK,
    Which types of shift registers can you purchase at your location.?

    I know that its not always possible to get all types locally.

    E
     
  5. eldadoh

    Thread Starter New Member

    May 2, 2014
    23
    0
    we got on lab 74LS91N
     
  6. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    The 74LS91 Shift Register is a Serial in , Serial Out type, it is not suitable for your project.

    A 74LS164 Serial In, Parallel Out is the shift register you need for 8 LED's and you can also connect two or more in series to light more LED's.

    E
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,804
    You may have some difficulty getting the restart behavior you want because you need to clear the contents of the shift register except for one bit. I haven't looked at the data sheet but if you've got a parallel load then you are fine.
     
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