timer circuit

Discussion in 'The Projects Forum' started by me111, May 11, 2012.

  1. me111

    Thread Starter New Member

    May 11, 2012
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    hey im new at this forum
    had to ask this one
    i have to make a project for which the object is to start a motor for 2 sec and then switch it off automatically even if the power supply stays on. i used the 555 in monostable mode for the purpose but i cant get it to switching off part.
    i need help ... PLEASE?
    here's the circuit i have been using


    [​IMG]
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Your attachment was unsuccessful. Please give it another try.

    hgmjr
     
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  3. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    heres a circuit for you to try- you need to change the timing components to suit for your application......and instead of the led substitute your motor and add a diode anode to collector ,cathode to supply on the op transistor.....you may also need to change the op transistor depending on the type of motor you are controlling....
     
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  4. me111

    Thread Starter New Member

    May 11, 2012
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    sorry for the image
    here it is again
     
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  5. me111

    Thread Starter New Member

    May 11, 2012
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    thank u SHELDONS
    im going to look into this circuit as well now
    hope it works
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    Often in a 555 monostable, pin 4 (Reset) is tied to +V. Why don't you try that before you give up on this circuit?
     
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  7. #12

    Expert

    Nov 30, 2010
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  8. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    if pin 4 is left floating the 555 might not work properly.....pin 4 is the reset pin which if not used must go to supply +(join pin 4 to pin 8),if you ground pin 4 the 555 is reset....heres an output stage you can play with as well with your circuit...
     
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  9. me111

    Thread Starter New Member

    May 11, 2012
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    im am working on first circuit that u gave with the LED.
    i dnt know where am i going wrong but the LED dsnt light for a single second :(
    im making the exact same circuit right now :|
     
  10. me111

    Thread Starter New Member

    May 11, 2012
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    and oh by the way i did connect pin 4 to V+ in the last circuit
    i attached an LED on the output with a 1K
    the LED did light up but it ddnt switch off then :|
     
  11. me111

    Thread Starter New Member

    May 11, 2012
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    the LED dsnt switch off :(
    i replaced the 220k pot and 10k and 1k and the 47uF on pin 6 and 7 and replaced it with and short them together and still its the same..
    where am i going wrong :(
     
  12. me111

    Thread Starter New Member

    May 11, 2012
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    and i havent even triggered it yet :(
     
  13. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Here is a schematic for a circuit that will work. For 2 seconds, change C1 to 100μf and R1 to 18kΩ. Or you can use your 1μF and 2megΩ for 2.2 seconds.

    ETA: I notice that you don't have a .1μF filter cap from pin 8 to ground. You need that, especially if you are using anything other than a battery for power. What is your power source?
     
    Last edited: May 13, 2012
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  14. me111

    Thread Starter New Member

    May 11, 2012
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    im using an 2 9V DC supply which are going into the 7812 to give out 12 v
    so it should work if a connect it directly right?
     
  15. wayneh

    Expert

    Sep 9, 2010
    12,126
    3,048
    Yes, although as the batteries age, or if you are powering more than just an LED, the voltage will likely drop below 12v. That's OK for the 555, I'm just saying...
     
  16. me111

    Thread Starter New Member

    May 11, 2012
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    555 works perfectly fine with 5v supply as well
     
  17. me111

    Thread Starter New Member

    May 11, 2012
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    AND YESSSSSSSSSSSSSSS!!! the circuit works now i hope it works with the rest of the mechanism
     
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