NE555 help

Discussion in 'The Projects Forum' started by tomoimrt, Dec 7, 2011.

  1. tomoimrt

    Thread Starter New Member

    Dec 1, 2011
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    0
    Hi,
    Is there an easy way to use the NE555 to generate pulse that gradually (exponentially rather than linearly preferred) increases from 1 Hz to 10Hz in 1 to 2 second and hold at 10Hz thereafter?

    Thank you for help in advance.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Pin 5 on a 555 can be used as a VCO. I'm not sure it will meet your design requirements, but it is worth a shot.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I'm wondering how you believe that ANY astable multivibrator can gradually increase from 1Hz to 10Hz in the span of 2 seconds?

    The 1st pulse would take up a whole second. The 2nd pulse takes 1/2 second. The 3rd takes 1/3 second, and the 4th takes 1/4 second, and you're over 2 seconds already.

    How did you plan on gradually ramping up to 10 Hz from that?

    Bill,
    Using pin 5 won't work for that wide of a frequency deviation. You might get 30-35%, but our OP wants far more.
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,871
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    I am the world's worst mathematician, but if the first pulse was 1 second (1 Hz), the second pulse was .5 second (2 Hz), the third pulse was .25 second (4 Hz), the fourth pulse was .125 second (8 Hz), the fifth and all subsequent pulses were .1 second (10 Hz), wouldn't that satisfy the OP's requirement?
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,145
    3,056
    +1
    I just completed a project that used pin 5 to vary frequency. With nothing applied to pin 5, my timer was configured to 0.65Hz at 50% duty cycle. Swinging pin 5 from ground to Vcc gave a calculated range of 0.42 to 1.06 Hz, or 0.67Hz ± 58%. The discharge time doesn't change, while the charge time does, meaning the duty cycle changes. That was fine for me but could be a problem in other applications.
     
  6. tomoimrt

    Thread Starter New Member

    Dec 1, 2011
    5
    0
    Thanks for all comments.
    I settled with 2Hz to 11Hz in 3 sec instead, with adequate off time separation between pulses.
     
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