how to create a 59 seconds timer

Discussion in 'Homework Help' started by Newfreak, Feb 6, 2010.

  1. Newfreak

    Thread Starter New Member

    Feb 6, 2010
    3
    0
    hey guys.
    im a fresh student of engineering and quite having problems on circuits.
    my project is to make a 59 seconds timer or 1 minute timer using 555, 74LS47 and 74LS190 .im going to dispplay the numbers using two 7 segments.

    my problem is i dont kow to make it stop at 5 and then loop again.


    please i need your help.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Monitor the output of the counter with a logic gates circuit. When its output reaches 59 the logic circuit will disable the 555 by driving its pin 4 low. The output of the logic circuit will feed a 2-input XNOR gate. The output of the XNOR gate will drive pin 4 of the 555. On the second input of the XNOR gate put a push button which will start the counting again when pressed.
     
  3. Newfreak

    Thread Starter New Member

    Feb 6, 2010
    3
    0
    please help me...

    im all new to this kinds of stuff...
     
  4. Newfreak

    Thread Starter New Member

    Feb 6, 2010
    3
    0
    thinking...

    its so hard for me but my professor told me it was easy..

    :D

    he told me to use only 74LS47,74LS190 and 74LS08, plus the 555 timer...
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Use Google to get data sheets for all those IC's - use "74ls47", etc as the search term.
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Think AND gate, feeding a reset (or a preset number, same thing).

    The number 5 is binary 101, which is not what you want. The binary number for six (110) would be where you reset.

    You could use a diode gate (they work well with TTL) or a TTL gate (qty 2 7400 gates, quad NAND).
     
  7. yasthicklee

    New Member

    Feb 6, 2010
    7
    0
    Hello friend,
    I feel this can make you good

    Just have a look at the image ...If u want i can give you the circuit too
    I dont know how to attach a image so i have done with a word doc
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    But that doesn't match his part requirements.

    The AND gate can pick up on the number I showed you (binary for 6), and feed into the reset pin.

    The 74190 is a pretty cool chip too, since you can make it start from any number. Reset takes it to binary 0, but you can treat the preload inputs as another form of reset, and take it to any number you choose.
     
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