reseting 555 timer

Discussion in 'General Electronics Chat' started by itel933, Sep 16, 2010.

  1. itel933

    Thread Starter Member

    Aug 26, 2010
    38
    0
    what do i need to connect in order to "reset" this circuit. I would prefer to use a push button. I know if I momentary connect negative to positive it resets the timer. is there another way to do it? FYI i dont have a swtich by the battery in the schematic, i eliminated the switch, that is why im looking for a way to reset it.....thanks
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Here you go. You can use any resistor between 10K and 47K.

    [​IMG]
     
  3. itel933

    Thread Starter Member

    Aug 26, 2010
    38
    0
    isnt that the same as just putting negative to positive though? what is being accomplished by just putting a resistor in series with a switch? does this mean that you can leave the push button pressed indefinately?
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    If you are just wanting to start the timing again short the capacitor connected to pin 2 with a push button. If you want precision add a resistor and another capacitor to feed a new signal using a standard configuration a monostable uses.

    Whenever you draw a schematic add designations, that way I can use part numbers to ID what I'm talking about instead of referring to that capacitor connected to pin 2.
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Of course not. Putting negative to positive will short circuit the whole power supply and will cause large current to flow. One must not deliberately try doing that, not even for a brief moment.

    A proper way to reset the 555 without affecting other circuit operation.

    Yes. Absolutely.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Quote Originally Posted by itel933
    what is being accomplished by just putting a resistor in series with a switch?

    A proper way to reset the 555 without affecting other circuit operation.


    Actually the /RESET pin must be held high for the 555 to operate, Normally it's just connected to pin 8 (+ of the power supply) but you need to use a pullup resistor if you intend to use it as an input, that keeps you from shorting out the power supply when you pull it low.

    Quote:Originally Posted by itel933
    does this mean that you can leave the push button pressed indefinately?

    Yes. Absolutely.


    Matter of fact holding the reset pin low is a way to keep the output pin low. It's just another control input available that could be useful in some circuit designs.
     
    Last edited: Sep 17, 2010
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