Change 555 circuit to NC

Discussion in 'The Projects Forum' started by haxxx, Feb 20, 2009.

  1. haxxx

    Thread Starter Active Member

    Feb 14, 2009
    35
    0
    Hey Guys,
    I just built the circuit on the right. How could i modify it
    to use a Normally closed trigger.
    Thanks,
    Haxxx
     
  2. JeffreyNHouston

    Member

    Feb 16, 2009
    26
    0
    Hello,

    I am a newbie. Just built a 555 circuit. I used a relay switch from the output to power a motor. The timer sets how long my output will stay on, then it goes off. I also discovered that moving the opposite relay pin delays how long the output is off, then the timer turns it on (and it stays on).

    I don't know if this observation will help you or not. But people have been so generous with their knowledge that I am eager to contribute.

    Jeffrey
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Use the left circuit and switch the position of the push button and the 47K resistor.
     
  4. haxxx

    Thread Starter Active Member

    Feb 14, 2009
    35
    0
    Correct me if i'm wrong but i think the problem with the one on the left
    is that the output doesn't go low if the if the trigger isn't returned to its orignal state. I want a normally closed one shot that will still timeout
    if the trigger is held open.
    Thanks
    Haxxx
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If you replace the 47K resistor with the NC push button and the NO push button with a 10K resistor it will work.
     
  6. haxxx

    Thread Starter Active Member

    Feb 14, 2009
    35
    0
    If this is what u meant i tried it,
    It doesn't timeout unless you release the switch
    Maybe i'm missin suppm, I don't know.
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    That is true. This is the reason you use a push button, you press it once as to trigger the 555 and then release it.
     
  8. haxxx

    Thread Starter Active Member

    Feb 14, 2009
    35
    0
    The actual trigger will be a photobeam with normally closed contacts.
    I was trying to avoid using a relay to get normally open.
    If an object is accidentally left between the sensors them my circuit won't time out.
     
  9. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Use a transistor to invert the output from the sensor.
     
  10. uguccione500

    New Member

    Mar 6, 2009
    2
    0
    Hello! I need to know how to build a simple (very simple, please, I'm 14!) timer that switch on a buzzer after 5 seconds it's powered by a 9v battery...
    It's my first circuits and I anything about ne555 timer... :(
    Thank You very much! :)
     
  11. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    First do not hijack others posts, start a new threat if you want help.

    You can use the circuit in figure 2 here:

    http://www.eleinmec.com/article.asp?4

    Replace the trigger button with a 100nF capacitor and connect the buzzer between pin 3 and Vs.
     
  12. uguccione500

    New Member

    Mar 6, 2009
    2
    0
    I'm very sorry for my mistake...
    I will thank you for the guide-line and the url: I go to watch surely soon...
    Thanks a lot... :)
     
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