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Simplest 2-LED alternating flasher

Discussion in 'Electronic Basics' started by Peter, Feb 25, 2007.

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  1. Peter

    Peter Guest

    I need the simplest possible circuit to make two LEDs flash
    alternately. About 1/2 second on each. I envisage using one flashing
    LED and one standard LED plus as few other components as possible.
    Maybe the 2 LEDs, one resistor and a mosfet.

    I have successfully used a flashing LED as the clock source for a 4017
    decade counter. Now I just want to make it and another LED flash. Any
    ideas much appreciated. Not interested in using 555's, NAND gates,
    schmitt triggers etc.
     
  2. Tom Biasi

    Tom Biasi Guest

    Well you have imposed quite a few restrictions.
    Maybe look at multivibrator circuits.
     
  3. John Fields

    John Fields Guest

    ---

    If you successfully got the LED to drive the counter, then this
    should work: (View in Courier)

    +V
    |
    [R]
    |
    [LED]
    |
    D
    FROM 4017 CLOCK INPUT>----G
    S
    |
    GND
     
  4. Guest


    Does the clock input go high when the flashing led is off?
    If it does connect a LED to the clk input and to GND...
    something like this maybe...


    VCC
    +
    |
    |
    .-.
    | |
    | |
    '-'
    |
    |
    |
    V -> Flashing LED
    -
    LED | .--o--.
    |-|<---|--|D S Q|
    | | |
    | -|> |
    === | R Q|
    GND '--o--'
     
  5. Peter

    Peter Guest

    Sorry, I didn't mean I want it related to a 4017. This is a completely
    separate exercise. I was just noting that I have successfully used a
    flashing LED to drive a 4017. My circuit was published in Australian
    Silicon Chip magazine in about 2004.

    I now just want to make 2 LEDs flash. Need it quickly so was hoping
    for a solution without having to experiment.
     
  6. Puckdropper

    Puckdropper Guest

    Take a look at this:
    http://mrollins.com/flash3.html

    Oh, btw, when you need it fast it's best not to ask on Usenet...
    Searching on the internet can get you results in less than 5 minutes. ;-)

    Puckdropper
     
  7. Peter

    Peter Guest

    I did search the web but found nothing. That circuit you referred to
    contains about 10 more components than I want to use. That looks like
    a standard astable multivibrator for which I agree there are thousands
    of circuits on the web. I am looking for something a bit unique.
     
  8. Lionel

    Lionel Guest

    The traditional method is an astable version of the classic 2
    transistor flipflop. If you want anything simpler, with fewer
    components (2x transistors, a couple of caps & a few resistors), &
    more unique than that, you're going to have to design something
    yourself.
    (There's any number of ways of flashing two LEDs with a single chip,
    but I can't think of any that are simpler than a 555.)
     
  9. John Fields

    John Fields Guest

    ---
    1. When you reply to a post, don't snip all of the post you're
    replying to, because that way no one knows what you're replying to.

    2. When you reply to a post that you've left some of the poster's
    text in for context, don't top post. So far you haven't been able
    to, but if you snip properly you probably will want to since you're
    a Google Grouper. For heaven's sake, read their stuff on posting to
    USENET.

    3. Pay attention when you read what someone gives you.

    For example, I posted:

    "If you successfully got the LED to drive the counter, then this
    should work: (View in Courier)

    +V
    |
    [R]
    |
    [LED]
    |
    D
    FROM 4017 CLOCK INPUT>----G
    S
    |
    GND"


    Notice that the gate of the MOSFET is connected to the 4017 input,
    which is also the output of the circuit you used to drive the 4017.

    Since you didn't show the circuit, one would have to guess how it
    was put together, but since you _know_ how it was put together all
    you need to do is connect the point driving the counter to the gate
    of the MOSFET.

    So, to get your 2 flashing LED circuit all you need is the LED
    flashing circuit you already have and the one I've given you.

    Maybe this'll make it easier:


    +V
    |
    [R]
    |
    [LED]
    |
    FROM THE PART OF THE D
    FLASHING LED CIRCUIT------G 2N7000
    WHICH WAS CONNECTED TO S
    THE 4017 CLOCK INPUT |
    GND
     
  10. Rich Grise

    Rich Grise Guest

    Oh, ick! 2N3055s to flash LEDs? OP could use 2N2222s, PN2222s, 2N3904s,
    2N4401s - practically any general-purpose tranny that will take the
    supply voltage and maybe 25 mA. They're so common you could almost find
    them lying in the street. ;-)

    Here's a sort of generic thing on astables:
    http://www.play-hookey.com/digital/experiments/rtl_astable.html

    Have Fun!
    Rich
     
  11. jasen

    jasen Guest

    ---+--------+---- 5V
    | |
    | [220R]
    self- | |
    flashing V .---+
    LED T / |
    | |/ |
    +-| V ordinary
    | |\| T LED
    | ~\ |
    | | |
    [1K] | |
    | | |
    ----+----+---+- 0V

    you may not need the 1K resistor.


    Bye.
    Jasen
     
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