Square Wave to 555

Discussion in 'The Projects Forum' started by Smijo, Nov 15, 2012.

  1. Smijo

    Thread Starter New Member

    Nov 15, 2012
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    I have a project where I'm taking a square wave output from an IR detector and I need some way to use that signal to trigger a 555 timer in astable mode. I think I need to connect the output of the detector to Vcc of the 555 (5V), but I'm not sure how or if that is right. I have the 555 circuits figured out and they simulated correctly. Does anyone have any ideas?
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    There are dozens (maybe hundreds) of ways to use a 555. What do you want it to do?

    What is the voltage and frequency of the square wave?
     
  3. Smijo

    Thread Starter New Member

    Nov 15, 2012
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    I want it to blink an LED, and another two wired to create a siren from a piezo transducer. I believe the frequency of the square wave is 1250Hz, and it should be 5V.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    "....trigger a 555 timer in astable mode".????
    It does not make sense. A monostable 555 is triggered. An astable oscillator is not triggered, instead it is turned on and turned off.
     
  5. Smijo

    Thread Starter New Member

    Nov 15, 2012
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    That's what I meant. I just need to have the timers turn on when the IR detector senses IR light. i.e. blink the LED and sound the siren.
     
  6. Smijo

    Thread Starter New Member

    Nov 15, 2012
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    Any ideas? Thanks.
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    You can turn an astable 555 on and off by controlling the reset pin.
    Vreset=0: Oscillator off
    Vreset=vcc: oscillator on
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    From some of my experiments with 555's 0.7VDC is a high to the reset pin (pin 4). You don't need much.
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    You can also hold the 555 cap either high or low to stop the astable, a diode is enough (between the square wave signal and the cap).

    That does require that the square wave is able to drive the cap, so it needs to "overcome" the 555 driving the cap, which is normally fine as the 555 would have fairly high value resistors driving the cap and the square wave is usually a logic output pin (with low resistance).
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    One of the most difficult things to do is to be able to explain completely what you have in mind to someone who cannot read your mind. This requires a certain degree of communications skills.

    Forget about the 555.

    Tell us what you want to do with the IR detector with no reference to hardware or chips.

    Draw a block diagram.

    Otherwise I have no idea what you are trying to say.
     
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