555 - Using the same switch???

Discussion in 'The Projects Forum' started by rokz_2005, Jun 2, 2011.

  1. rokz_2005

    Thread Starter Member

    May 14, 2011
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    How can I use the same power switch to reset/stop a monostable output/pulse

    eg from the schematics below.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    It would need to be a single-pole, double-throw, center off switch that is spring loaded to return to center.

    One side of the switch would short pin 2 to ground.
    The other side would short pins 6 & 7 and the top of the 10uF cap to ground.

    Why not just use two separate N.O. momentary pushbuttons?
     
  3. rokz_2005

    Thread Starter Member

    May 14, 2011
    68
    0
    Thanks for the reply.

    I don't want to use too many buttons. I'm kind of fussy.
    And the other thing is when I'm faced with a problem I try to resolve it according to my original plan :) (even though I know the easier option would have been to add another switch :p

    I've also had an idea, I don't know how well this will work...
    What if I have a capacitor (right size) attached to the switch so I will have to hold for 1second. have the same switch connected to PIN 4 (reset).
    In theory (well in my head) It looks like, while I'm charging up the capacitor I would also be trying to 'Reset' but as there are no current flowing I would not be actually resetting anything however if the timer is running and I simply press the switch it would trigger a reset, wouldn't it??
    I could maybe add a cut off for 250ms on PIN 4 so that the circuit would not conflict (as in one pin trying to turn it on and the other trying to reset at the same time)

    What do you think
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Why don't you try it and see?
    After all, switches and 555 timers are cheap, so it doesn't matter if you burn up a few dozen of them, right?

    I told you the solution already; one switch that has two poles, that is spring-loaded to the center off position.
     
  5. rokz_2005

    Thread Starter Member

    May 14, 2011
    68
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    I'm just waiting for all my parts to come through, I shall be burning a few bits n bob hehe
    Should be fun and of course I will update the thread with the project.

    Quick question... by any chance do you know if PIN 4 has the same input voltage as PIN 2 or do I need to put a resistor in between as well?

    or

    How do I get PIN 4 to reset the circuit. By drawing or pumping electric into it?

    I'l let you know how it goes
     
    Last edited: Jun 2, 2011
  6. Wendy

    Moderator

    Mar 24, 2008
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    You can not ignore pin 4. It must be connected to Vcc, either directly or indirectly (through a resistor). We had a similar problem on another thread.
     
  7. rokz_2005

    Thread Starter Member

    May 14, 2011
    68
    0
    Possible answer to my question???

    Adding a relay or a transistor or a TRIAC to pin 4 which will cut power when the switch is pushed? By the time the capacitor charges up for the timer, the user can let go of the switch which will bring pin 4 back up to high and the circuit operational

    Will that work?
     
    Last edited: Jun 5, 2011
  8. simo_x

    Member

    Dec 23, 2010
    200
    6
    Your circuit is ok. I made it and you edited some string :D
    If you want to stop the 555 just push the switch & it will stop to work.
    If you want to stop it for an undetermined time, put a normal switch.
    Regards
    Simo
     
  9. rokz_2005

    Thread Starter Member

    May 14, 2011
    68
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    Yup, thanks for that.

    I could do that with another switch but im thinking there must be a way to use the same switch.
     
  10. rokz_2005

    Thread Starter Member

    May 14, 2011
    68
    0
    OK I'm a little bit confused.

    Whats the difference in characteristic between the two circuits?
     
  11. rokz_2005

    Thread Starter Member

    May 14, 2011
    68
    0
    Would this allow me to start and reset the timer with one switch?

    I haven't got the schematics for the delay but in this case you would have to push and hold the switch for 1 second then the timer starts. Therefore I don't think that the reset button and power on button will conflict.
    And yes, the 'NO' will not be connected to anything therefore when the switch is pressed. there will be no power to PIN 4.

    Can someone also tell me where how to add a 1second delay to the swicth for the timer please. thanks
     
    Last edited: Jun 8, 2011
  12. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    [​IMG]

    It appears to me that you will create a dead short with one configuration, and leave pin 2 floating for another.

    This may be a dead thread, I just came across it scanning through, but if it is still active it needs work.
     
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