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Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Abeer_engjbr, Feb 10, 2008.

  1. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Its the collector load resistor for Q1 transistor.

    When Q1 base receives a postive signal it conducts and pulls the RESET line low, which RESET's the 555.
     
  2. Abeer_engjbr

    Abeer_engjbr New Member

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    what is the purpose of 47 micro capacitor on the 555 timer,
    and why the DIS pin not connected to anything, and why they used one resistor with the 555 instead of 2 as in astable mode.
     
  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    The 47uF is decoupling the 12V

    The DIS pin is not connected as the 555 is not being used as a conventional astable

    Its not an conventional astable.


    EDIT: the text with the circuit diagram explains the function of the 555
     
    Last edited: May 14, 2008
  4. dave

    Dave New Member

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  5. Abeer_engjbr

    Abeer_engjbr New Member

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    what is decoupling cap? what does it do?
    and what do you mean by conventional astable? and if i want to explain about why in this circuit I didn't use the equations that establish the values of the resistors and capacitors , what must I say ?
     
  6. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi Abeer_engjbr,
    May I ask what subject you are studying and the year you are in.?:)

    I would like to help, but if you dont know the basics its going to be difficult..:rolleyes:
     
  7. Abeer_engjbr

    Abeer_engjbr New Member

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    I am a senior , but i used this circuit in my project and I need to know evrdetail about it, to be able to answer any question.
    If you may answer on my last reply please am such in a hurry and am running out of time.
    Thanks.
     
  8. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    The attached jpg shows the formula for the timing also it explains that the 555 is connected as an oscillator with an equal marl/space ratio [On/Off]

    The 47uF is on the circuit in order to hold the +12V line at a 'constant' voltage as each part of the circuit draws current from the +12V, especially the IR LED drivers.
    Without the 47uF, every time the IR pulsed the +12V would drop slightly in voltage, this could affect the 555 timing..OK
     
    Last edited: Jul 7, 2008
  9. Abeer_engjbr

    Abeer_engjbr New Member

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    Demodulation by IR Reciever

    Hi everybody,

    I need to know how does an IR reciever do demodulation? what is the process of the demodulation?

    The datasheet for it is attached and it is used in following circuit:
    IR Remote Control Extender Circuit (Mark 4)

    Thanks
     

    Attached Files:

  10. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Yes, it removes the 38kHz carrier. It is also active low out and has a built in pullup. I use them in my Junebug & Firefly kits. You also need the 100ohm & 4.7uF cap on its power pin if you're powering it from 5V.
     
    Last edited: May 23, 2008
  11. Abeer_engjbr

    Abeer_engjbr New Member

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    Hi,
    I know that it removes the 38 kHz , but how that is my question.
     
  12. blueroomelectronics

    blueroomelectronics Well-Known Member

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    It describes it in the datasheet far better than I could. So your school allows handing in other peoples designs and taking credit for it as long as you can explain how it works?
     
  13. Abeer_engjbr

    Abeer_engjbr New Member

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    Yes, it does. Was it a sarcastic question?
     
  14. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Well I guess education standards vary pretty wildly from place to place. If this is a University that's really sad. For Grade school it's fine.
     
  15. Abeer_engjbr

    Abeer_engjbr New Member

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    Hi,
    Thanks for your care, I've just finished my graduating project, and the IR repeater circuit is just a part of it.

    This website (electro-tech-online) helped me alot realy, and I am thankful for that.

    I've included in the project documentation that I did not bulit the circuit and included the link for it in the references.

    And according to the fact that they, the Doctors, might ask me anything even if i did not design it , make me ask about everything that comes through my mind.

    Thank you again, and wish me luck because my presentation is on Tusday.
     
  16. blueroomelectronics

    blueroomelectronics Well-Known Member

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    IR demodulator ICs are pretty handy, a fair amount of stuff inside those things.
    Good luck, what course are you graduating?
     
  17. Abeer_engjbr

    Abeer_engjbr New Member

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    Communication engineering.

    I want to ask you , in the sildes that i'll use for my presentation I've included only the headlines and pictures and I'll explain everthing with the help of somepapers I wrote to keep me fom forgetting anything, and I'll practice in front of my colleges before the presentation.

    Is that considered good ?
     

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