Step down from 5V to 0V and then to 5V again

Discussion in 'General Electronics Chat' started by manorius, Apr 29, 2009.

  1. manorius

    Thread Starter New Member

    Apr 28, 2009
    5
    0
    Hi,

    I'm new to this forum and quite new to the electronics,
    the only circuits I have created from scratch are relies
    with 555 timers for my art projects, so please have some understanding
    for my lack of knowledge :).

    For a project I have a 5V LED and I would like to make a very small
    circuit maybe one microchip big (space is an issue), to turn gradually on and then off (like the mac led when on sleep mode). Is there a chip that I can use to achieve this or is there a schematic for a small circuit that I could follow?

    Thanks a lot!
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Welcome to AAC!!:)

    Just a stray thought... The 556 is a single chip with two 555 timers on-board.

    IF...

    If both timers were configured as astables, one fairly slow and one rather fast,

    AND

    and the capacitor voltage of the slow one (on either "Trigger" or "Threshold") were connected to "Control Voltage" of the fast one one...

    ...wouldn't the output of the fast one be pulse-width-modulated by the slow one's charge-discharge curve? Thereby making any LED hooked to it gradually dim and brighten alternately?
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,577
    231
    Probably the smallest would be an 8-pin PIC, or other μcontroller, outputting a swept PWM, driving your 5V LED...battery, μcontroller, bypass capacitor, and the LED. The battery(s) will be the biggest component, and depends on how bright you want the LED to shine.

    Ken
     
  4. manorius

    Thread Starter New Member

    Apr 28, 2009
    5
    0
    Thanks a lot Ken, do you have any links or forum posts with more information re pic controller?

    Cheers
     
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,577
    231
    I play with PICAXEs. They're Microchip PICs with a built-in interpreter. The 8-pin "08M" is about $3.50 and requires only a 3-wire serial cable and two resistors to program, with a free BASIC language editor/simulator on a PC. Their forum is very active and helpful: http://www.picaxeforum.co.uk/ Search there on: fading led. It's already been done.

    Ken
     
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