74ls08 giving output without inputs

Discussion in 'Homework Help' started by 13ME15, Apr 11, 2016.

  1. 13ME15

    Thread Starter New Member

    Apr 11, 2016
    3
    0
    Hello everyone,

    This is my first electronics project.
    I am using 74ls08 AND logic gate, The Vcc is 4.5 V with no resistors, Now when I'm giving two inputs at pins 1 and 2, I get True(1) at the pin 3. When I remove any of my input, I still get True output. If I'm removing both of my inputs even then the result is coming out to be true. I don't understand what is happening with the Gate IC.
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
    821
    229
    Don't "float" the inputs.
     
  3. 13ME15

    Thread Starter New Member

    Apr 11, 2016
    3
    0
    Can you please elaborate it, how can I avoid floating of inputs?
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,363
    How do you know what is the logic input when nothing is connected?
    Is it 0 or is it 1?

    Better to make sure.

    For 0 input, connect it to GND.
    For 1 input, connect it to Vcc.

    No connection means the input is floating.
     
  5. 13ME15

    Thread Starter New Member

    Apr 11, 2016
    3
    0
    Thanks a lot man you saved my day.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,033
    3,241
    With CMOS logic an open input is indeterminate, it could be a 1 or 0 or in-between.

    With bipolar TTL logic you have to sink current for a logic 0.
    An open TTL input normally goes to a logic 1.
     
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