timer retriggering

Discussion in 'The Projects Forum' started by kiranr, May 30, 2009.

  1. kiranr

    Thread Starter Member

    May 1, 2009
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    Correct me if someting is wrong
    I am making an ir obstacle detector to find if someone is standing in front of my door.I used a 555 monostable for a 30s output and an HS0038 module as sensor.As for the transmitting,after testing with some 555 astables ,I could'nt get the needed reange so I just used a tv remote instead.Since the reflecing surface is uneven I paralleled 8 ir leds to the remote's led through a transistor.

    I have a constant power supply from a big 12v battery and i used 7805 for 5v outputs -one for transmitter and another for reciever.However , when i conect the two input leads together, (I suspect)that the high current change due to on-off of the 8 leds is causing the input to fluctuate.This is retriggering the 555 monostable.If I remove the extra leds there is no problem.

    Please suggest some way to manage this fluctation
    [​IMG]
     
    Last edited: May 31, 2009
  2. kiranr

    Thread Starter Member

    May 1, 2009
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    0
    somebody please help!!!!!!!!!!!!!!!!!!!!!!
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    Whenever post a question about a specific schematic it helps to post the schematic in question, gets the ideas flowing.

    If you are looking for a new way to do this, define the function without being too narrow about how to go about it.

    The 30 IR LEDs would work better than TV remote. I suspect you need to modulate them with a simple square wave. Detecting a specific frequency is a lot simplier, and cuts down on the extranious signals.
     
  4. kiranr

    Thread Starter Member

    May 1, 2009
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    I am using the tv remote to use the 38khz modulated signal.The HS0038 (TSOP1738) senses only that frequency.I m using 8 not 30 leds in parallel so that i can enusre ir reflection from a greater angle.i have connected them.

    the problem is that the remote is giving high current to the leds(more than the rated current becuz the duty cycle is short) and since such a high current (not sure how much) is switched on/off at 38 khz there is interruption in the supply and the 30s timer is retriggering continuously
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Again, schematic on the LEDs?
     
  6. kiranr

    Thread Starter Member

    May 1, 2009
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    sry ,don't know why it didn't appear first
     
  7. Wendy

    Moderator

    Mar 24, 2008
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  8. kiranr

    Thread Starter Member

    May 1, 2009
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  9. Wendy

    Moderator

    Mar 24, 2008
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    I get the screenshot below when I click on the link.

    Try saving your file using a .png or .gif format and upload it as an attachment.

    This site is probably one of the most open ended in letting you use attachments. We even have an albums section, which is a free image hosting site.
     
  10. kiranr

    Thread Starter Member

    May 1, 2009
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    sry for asking but how do i use the album?
     
  11. kiranr

    Thread Starter Member

    May 1, 2009
    25
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    got it
    its too big as a pic
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    That's why you use the alternate format's I suggested. .gif and .png are both compressed formats, and work very well.
     
  13. kiranr

    Thread Starter Member

    May 1, 2009
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    hope this works
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    It works well...

    [​IMG]

    Give us a little time to study it now.
     
  15. kiranr

    Thread Starter Member

    May 1, 2009
    25
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    thanks for the interest
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    OK, first thing, you didn't draw it, so I am guessing you have 8 LEDs directly in parallel, with no resistors. This is a no no.

    Try reading my tutorial, especially the section on LEDs.

    LEDs, 555s, Flashers, and Light Chasers

    My blog is Bill's Index.

    BTW, welcome aboard. You'll find we are a friendly group, and will work with you to help.

    I've got to go for a while, but I'll be back.
     
  17. kiranr

    Thread Starter Member

    May 1, 2009
    25
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    actually when i connected the resistors the output was not strong enough so i bypassed it.
    first i had given a resistor for each of the leds.
    i didn't think of series becuz then how will i get enough total voltage of 8x2.5=20v
     
    Last edited: May 31, 2009
  18. Wendy

    Moderator

    Mar 24, 2008
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    Your LEDs are probably blown out then, or severly damaged. I strongly recommend you read the tutorial. Resistors are not optional.
     
  19. kiranr

    Thread Starter Member

    May 1, 2009
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    the leds are not blown out bcuz i checked them with a digital camera.they r working but causing severe fluctuations in the supply.the resistors are not blown out even with a very high current bcuz as i have read elsewhere the duty cylce is short enough to let the leds cool down even with the high current

    If this is wrong please correct me

    I am not facing problem with transmission or detection rather the fluctuation is causing the 555 input to go low and when it comes, it triggers the timer
     
  20. Wendy

    Moderator

    Mar 24, 2008
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    LEDs aren't necessarily go/no go, if you damaged them they will be dimmer. At the risk of repeating myself, you can not run LEDs with out resistors without damaging them. If you are still trying to do this then you may have fried your 555 also. So what is you're current power supply and resistor setup?

    Another thought occurred, it could be your fluxiations are the power supply sourcing too much current when the turns on, they need resistors too. If you are shorting the power supply the regulators can't prevent it, that is not their job.
     
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