555 delay between restart

Discussion in 'General Electronics Chat' started by TheDag, Apr 12, 2012.

  1. TheDag

    Thread Starter Member

    Jan 1, 2010
    94
    1
    Hi,
    I Have 555 monostable circuit, when 12v input, its pulse for 5 seconds....
    now,
    If im unplug the voltage source and plug it again quick, its not work...
    I have to wait 1-2 seconds before i plug the voltage source in again....
    I Want it to be without delay, i think its something with the capacitors.....

    Please Help, Thanks.
     
  2. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Try this:
    The 470Ω discharges the power supply quickly.
    The diode discharges the timing capacitor quickly.
    Beyond that, reduce the value of the timing capacitor while increasing the timing resistor.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    If you were to put a back biased diode across R3 it would discharge the capacitor it the power supply were shorted when turned off. This would do what you want.
     
  4. TheDag

    Thread Starter Member

    Jan 1, 2010
    94
    1
    can you expand please?
    BTW, The pin 7 not connected to anything, maybe this is the problem?
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Pin 7 is a open collector.

    The reason you have to wait a while is the capacitor has a charge on it. You need a way of discharging it, which posts #2 and #3 explained how to accomplish.

    Try Jim's circuit, it will work if wired correctly.

    This is a power on delay circuit, it resembles a monostable, but you have tied the trigger (pin 2) to pin 6 instead of the classic 555 monostable circuit.

    There is another way to do it, if you are interested.
     
  6. TheDag

    Thread Starter Member

    Jan 1, 2010
    94
    1
    I Will be glad for another way....
    BTW, 1n4001 its ok to use for jim's circuit ?
     
  7. Wendy

    Moderator

    Mar 24, 2008
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  8. TheDag

    Thread Starter Member

    Jan 1, 2010
    94
    1
    in jim's circuit,
    i can connect the resistor just to battery + and battery - ?
    or its must be beside the capacitor and potentiometer ?
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    Yes. It is the same thing. Schematics are not about physical locations.

    Do be aware of a switch if you have one though, you do not want the resistor on the wrong side of the switch.
     
  10. TheDag

    Thread Starter Member

    Jan 1, 2010
    94
    1
    Thank you both, Works great ! (jim's circuit)
     
  11. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Now to reduce battery current, you can start increasing the 470Ω resistor until it malfunctions in order to determine maximum value.
     
  12. TheDag

    Thread Starter Member

    Jan 1, 2010
    94
    1
    What do you mean reduce battery current?
    Why do I need to reduce that?
     
  13. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Longer battery life--that is all--you indicated that you were running from a battery
     
  14. TheDag

    Thread Starter Member

    Jan 1, 2010
    94
    1
    if before the 555 i have 12v to 9v.
    Can i put the resistor and the diode in the 12v from the beggining and its will still work ?
     
  15. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    probably not
     
  16. TheDag

    Thread Starter Member

    Jan 1, 2010
    94
    1
    for fast discharging lm317 circuit
    which capacitor i should discharge?
    470ohm resistor between vOut and GND, and where the diode goes to ?
    [​IMG]
     
  17. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    diode goes to Vout
    470Ω goes between Vout and Gnd
    Since you have power to burn, no need to adj resistor value up
     
  18. TheDag

    Thread Starter Member

    Jan 1, 2010
    94
    1
    Sorry, I Miss understood the last line......
    Btw, why you not connecting to the MSN ?
     
  19. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    Since you have excess power available there is no need to adjust resistor value.

    I have only hotmail--just added you as friend--do not know what this buys
     
  20. Wendy

    Moderator

    Mar 24, 2008
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    Jim was referring you to the fact that a 470Ω resistor is a drain on your battery. It is assumed you want your battery to last as long as possible.

    In all circuits like this there is compromise, you need the 470Ω resistor to drain the capacitor when there is no power, but that same resistor will drain your battery when the power is on.

    If you had a power switch that connected the two power rails (+ and -) together when the power was off you could eliminate the 470Ω resistor and the power drain.
     
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