Countdown timer to BCD decoder.. the output 5-0 only

Discussion in 'The Projects Forum' started by ofakera, Oct 3, 2012.

  1. ofakera

    Thread Starter New Member

    Aug 25, 2012
    2
    0
    good day.
    I need to know how can i make the 4bit down counter to BCD to 7 segment decoder output goes from 0 to 5 only.

    Is it possible?
    I cant think of a good logic for it.
    any suggestions? Thank you !!

    i am using
    74LS190(SYNCHRONOUS UP/DOWN COUNTER)
    74LS47(BCD to 7 segment decoder)
     
  2. panic mode

    Senior Member

    Oct 10, 2011
    1,321
    304
    read datasheet. preset counter to value you want (5) then count down...
    pin 5 selects direction of counting. to count down, pin 5 needs to be high.
    then just use 74ls47 to decode counter output of counter.
     
  3. ofakera

    Thread Starter New Member

    Aug 25, 2012
    2
    0
    thanks to your response. but i already know that. my problem is the decade counter counts 10 states so when decoded it also has ten outputs. i am also done setting it from 5-0 down counter but after the 6th state count of the decade counter the output is messed up.
     
  4. MrCarlos

    Active Member

    Jan 2, 2010
    400
    134
    Oh very well, but after reaching the 5 the 74LS190 what should do??
    Stop??
    Start again at five and go to zero? over and over.

    regards
    at your service
     
  5. panic mode

    Senior Member

    Oct 10, 2011
    1,321
    304
    Pn inputs are parallel preset inputs (P3, P2,P1,P0).
    connect them to low and high combination representing binary code you want to load. if you want to start from 5, load binary value for 5 (that is 0101).
    in other words pins P3 and P1 need to be tied to low (pins 9, 1), while pins P2 and P0 to high (pins 10 and 15).

    now whenever you trigger preset (PL=low, which is pin 11). that binary value "0101" will be loaded into counter.

    then you happily count down until you are done. this state need to be detected and used to trigger PL. for example you can use OR gate with inputs tied to counter outputs. if outputs are anything but "0000", PL will be high and inactive. but once the counter reaches "0000", PL will go low and load five ("0101" in this case).
     
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