Help with counter circuit?

Discussion in 'The Projects Forum' started by SevenSeas, Jun 6, 2015.

  1. SevenSeas

    Thread Starter New Member

    Jun 20, 2013
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    Hi guys,

    I'm trying to prototype a 7 segments display counter with 555 timer circuit using multisim and the circuit works but it counts in multiples of 2 and I have no idea why. Any chance you guys can take a look and help me figure out why?

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  2. JohnInTX

    Moderator

    Jun 26, 2012
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    My guess is that you have INA (pin 14) connected to QA (pin 12). The LS90 will count on INA and/or INB so I think its picking up QA as an additional clock edge.
     
  3. SevenSeas

    Thread Starter New Member

    Jun 20, 2013
    5
    0
    Thanks for your suggestion but it didn't work. It maybe sometime I'm doing wrong with multisim itself as I have very little experience with it.
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    What didn't work?
    How did you change the schematic?
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The 7490 is actually two independent counters, and you have them connected incorrectly. The 555 clock goes to IN-A, and the QA output goes to IN-B.

    ak
     
    JohnInTX and SevenSeas like this.
  6. SevenSeas

    Thread Starter New Member

    Jun 20, 2013
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    Thank you very much it's working perfect now.
     
  7. JohnInTX

    Moderator

    Jun 26, 2012
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    Ha! I thought I remembered how they work. Sorry for not checking the actual datasheet. Thanks, AK
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
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    A lot of counter schematics floating around; show inA driven by Qd, you still get an overall divide by ten but the output has 50:50 mark space ratio.
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    That was the clue.

    ak
     
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