555 Timer Circuit, too slow to reset.

Discussion in 'The Projects Forum' started by Markw996, Aug 28, 2011.

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  1. Markw996

    Thread Starter New Member

    Dec 20, 2009

    I have found a simple 555 Delay-On circuit on this website, I hope to use it to filter out a series of approx ten 0.5s pulses of 12v before the supply either turns off, or turns on and becomes a positive supply.

    The problem is that the capacitor doesn't discharge fast enough, and so becomes fully charged after maybe 5 or 6 pulses causing the output to pulse for the remaining 4 or 5 pulses before becoming stable.

    Could I add something to the circuit to make the capacitor discharge (completely) between pulses without affecting the delay period, or should I be looking at the problem from a different ange, i.e. a different circuit?


    Last edited: Aug 28, 2011
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    1. It would be interesting to know what power supply this is and what's the time between the 0.5s pulses.

    2. Does the voltage go to zero between the pulses?

    3. What are the values for Ra and C?
  3. Markw996

    Thread Starter New Member

    Dec 20, 2009
    1. The power supply is from my car, the pulses are caused by the 'bulb check' monitoring computer.

    2. Yes it does drop to zero between pulses.

    3. At the moment I am just testing the theory on my breadboard, the values are 470k and 4.7uF to give a 3 second ON delay.
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
    What's the time between the 0.5s pulses?
  5. SgtWookie


    Jul 17, 2007
    From what you said in the post I quoted, this must be an automotive modification project which we do not support, in accordance with the Terms of Service paragraph 6.
  6. bertus


    Apr 5, 2008

    I am closing this thread as it violates AAC policy and/or safety issues.

    6. Restricted topics. The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

    • Any kind of over-unity devices and systems
    • Automotive modifications
    • Devices designed to electrocute or shock another person
    • LEDs to mains
    • Phone jammers
    • Rail guns and high-energy projectile devices
    • Transformer-less power supplies
    This comes from our Tos:
    Terms of Service
    There will be enough sites where automotive questions can be discussed :
    Member selected automotive forums

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