urgent help regarding SR latch

Discussion in 'General Electronics Chat' started by vivek.raunak, Jan 27, 2011.

  1. vivek.raunak

    Thread Starter New Member

    Oct 23, 2010
    29
    0
    hi,
    i am doing a project,in which SR latch is needed.
    i used cross connected nor gate.(actually and gate with not gate...not having nor gate)i am using ic7404 and 7432.
    but still not getting output...
    is there problem with propagation delay?
    please help........
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I do not see your schematic of your circuit.
    I do not see a photo of how you have it connected.

    There are many variants of the 74xx series. Are you actually using 7404, or is it 74HC04, 74LS04, or something else? Give the entire part numbers of the actual components that you are using.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,777
    932
    Urgent or not, your question begs for details, details, and still more details. This is also why pictures and schematics are asked for.

    You mentioned IC's. Are they good? do you have a test circuit to verify IC operation? Do you have test equipment other than DVM? O-scope? Logic probe? :(

    Good help will require a GOOD description of circuit and all the details.
     
  4. vivek.raunak

    Thread Starter New Member

    Oct 23, 2010
    29
    0
    i attached my circuit .
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    That is partly correct. It would be simpler if you selected a 7402, which is a NOR gate.

    No pin numbers are given, plus the inputs are floating. The R-S latch only works if one input is HIGH while the other is LOW.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You must use pull-down resistors (somewhere between 330 Ohms and 10k Ohms depending upon the full part number) on the S and R inputs to keep them low by default.

    When you want to S or R the flip-flop, you can switch the desired functions' input to Vcc.

    The circuit will be in an unpredictable state when first powered up.
     
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