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Use a schmitt trigger for turn on / off slowly LEDs with an automatic duty cycle

Discussion in 'Electronics Homework Help' started by xAmaranx, Jun 9, 2016.

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  1. xAmaranx

    xAmaranx

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    Jun 9, 2016
    This its my ckt I have already achieved the LEDs on and off slowly, but I do not get is that the work cycle is automatic please give me a help
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

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  3. xAmaranx

    xAmaranx

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    Jun 9, 2016
    Im using 100kΩ
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    That should give a frequency of ~0.18Hz.
    Check the inputs to the other (unused) gates of the 40106. They should be tied to ground or Vcc, never left unconnected.
    Check the output of the 40106 before the RC filter (R1, C3).
     
  5. xAmaranx

    xAmaranx

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    Jun 9, 2016
    hi mister, this it's the signal between R1 and C3
     

    Attached Files:

  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I would consider using a mosfet in this circuit. It would allow the turn on and turn off to be relatively symmetrical.

    as it is now, the LEDs are likely to turn off faster than they turn on.
     
  7. xAmaranx

    xAmaranx

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    Jun 9, 2016
    This its a designar that i'll make i have no traying to use a MOSFET; someobe told me that MOSFET will make more stable the current on all leds xD, but i need that all led turn on abd off slowly and change the automatly duty cycle
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

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    This looks o.k. What then is your issue with 'I do not get is that the work cycle is automatic'?
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Check out the circuit near the bottom of this page
     
    hevans1944 and Harald Kapp like this.
  10. xAmaranx

    xAmaranx

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    Jun 9, 2016
    My problem it's the automáticamente duty cycle, i was think using a counter or FF jk in the signal out of the trigeer.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I don't understand. What is your problem?
     
  12. xAmaranx

    xAmaranx

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    Jun 9, 2016
    I need to do an automatic duty cycle on this ckt
     
  13. Harald Kapp

    Harald Kapp Moderator Moderator

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    Please explain: What is an 'automatic duty cycle' to you? We are not familiar with this term, so what is the circuit expected to do?
     
  14. xAmaranx

    xAmaranx

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    Jun 9, 2016
    Ok the ckt most be
    "Use a schmitt trigger for turn on / off slowly LEDs with an automatic duty cycle"

    I need to change the duty cycle on the exit for turn on/off led in different moment's

    Unwatch Thread
     
  15. Harald Kapp

    Harald Kapp Moderator Moderator

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    What I can imagine is that the task description calls for a completely different solution: An LED where the intensity is controlled by a PWM signal. To turn the LED slowly on or off, the duty cycle of the PWM needs to be controlled automatically (e.g. by a ramp). Is this what you are looking for?
    The principle is shown here:
    upload_2016-6-10_8-9-18.png
    The blue line is the ramp signal: slow turn-on, stay on for some time, slow turn-off.
    The triangular signal (not shwon in the diagram) would be a fast triangle wave with a frequency e.g. >100Hz to make the resulting flicker of the LEDs invisible to the human eye.
    The comparator creates the PWM with 'automatically changing duty cycle' to turn the output power slowly on or off.

    I suspect this is homework or an assignement (given the task description in your last post). I will therefore:
    • Move the thread to the homework section
    • Not diclose the complete circuit. From the above principle, design your own circuit. Show us your effort and we'll gladly help you fill in the gaps.
     
    Last edited: Jun 10, 2016
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