LED timer circuit...Please help

Discussion in 'The Projects Forum' started by Abhi_12, Nov 24, 2009.

  1. Abhi_12

    Thread Starter New Member

    Nov 24, 2009
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    Hi all, thank you in advance for your help in these simple projects that i need help for...
    I beg your pardon in advance that I am not from electrical field and a complete novice in this, so any help is hugely appreciated..
    Ok this is what I need:

    I have 1 LED(small 3mm LED), that will be powered by 3 1.5 volt button cells and 1 switch.
    What i need-

    1. After a switch on the LED, it automatically switches off after 2 minutes.
    The circuit needs to be really simple and small, overall it should fit into a tube 17-18mm in diameter.

    2. After switching on, the LED fades-in to full glow in about 30 secs and stays in full glow till switched off. again, overall it should fit in a tube 17-18 mm in diameter.

    3. How can i make the LED blink or pulse while its on?

    I know i am asking for too many solutions in 1 go but i really really need the help..thank you all...
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    A CMOS 555 will come close, but you need to break it down a bit. Why all the functions?

    A modern white LED takes around 3.6 V, this could be a problem. Not insoluble, but it will need work.
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    I would say a small 8 pin PIC micro-controller will do the job nice. But one drawback is that it must be programmed by someone to do this job
    Just a tip ;)
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    You know, I don't usually go with µC, but in this case it does make sense. Do they go that low on voltage?

    It will have to use BJTs, since it is below what a MOSFET can use (unless I'm mistaken).
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    My locale component pusher have the 12F629/12F675. I have used them for something like the OP want. They will work in the range 2 to 5.5 volt
     
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