555 Monostable timing problem

Discussion in 'General Electronics Chat' started by secky, Feb 21, 2009.

  1. secky

    Thread Starter New Member

    Feb 21, 2009
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    Hi, I'm new to electronics and this forum.
    I'm trying out a 555 monostable on a breadboard. I'm using a 9V battery supply; output is a LED.

    The ON time for the 555 monostable is dependent on the RC value, with the t=1.1 (RxC) rite?

    The measured values of the resistor and capacitor are 4.9Mega Ohm and 12mirco Farad respectively, so the "t" should be about 65 seconds, but my LED only turn on for 11 seconds .

    Even if i replace the resistor with a smaller value, 500k, t should be 6.6 seconds but I got a time much lower than that. :confused:

    I've check my circuit connection many times. What could be the problem?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Post the schematic, you may think it is correct but it is not.
     
  4. secky

    Thread Starter New Member

    Feb 21, 2009
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