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Basic Circuit Question

Discussion in 'Electronic Basics' started by Jon, Jan 27, 2004.

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  1. Jon

    Jon Guest

    Hey

    I'm using a switch, 9V battery and an LED and I would like to have it
    so the LED blinks (or any type of oscillation). The problem is I
    don't want to get into ICs and such, since the 9V is my only source of
    power (and I dont want to do a DC-DC conversion). is there any way to
    do this with components like capacitors and resistors? (with time
    constant stuff perhaps?)
     

  2. Resistors and capacitors alone won't be able to make an oscillator. The
    reason for this is fundamental to electronic circuits and is mainly beacuse
    R's and C's are passive components. You need to throw an active component,
    such as a transistor, in the mix.

    Check out the circuits in this page:

    http://members.shaw.ca/roma/twenty-three.html

    They should get you going. Also, Google is your best friend...

    Costas
     
  3. Monk

    Monk Guest


    yah you need at least a transistor in there,

    google search -- R-C phase shift oscillator
    -- transistor Colpitts oscillator
    -- transistor Hartley oscillator (colpits is easier
    only one inductor)
    -- Pierce Crystal oscillator


    or you could go with 2 9v batteries and a op amp if you wanted too
    also i think that you could do a 555 timer as an astable multivibrator
    with a 9v (i think it would run at 9) don't know the current draw on
    them is so i dont know how long your battery would last tho.

    cheers,

    monk
     
  4. An LMC555 is perfect for this task, running directly off the 9 volt
    battery.

    The data sheet shows how to make an oscillator, figure 4 on page 5:

    http://cache.national.com/ds/LM/LMC555.pdf

    Connect the LED in series with a 1k resistor between the +9 volt line
    and the output pin. or between the -9 volt line and the output pin.
    The first is best for short pulses with longer time between, and the
    second is better for long pulses with shorter time between.

    Page 6 gets into the resistor and capacitor values needed versus pulse
    time and pulse frequency. This chip costs less than a dollar and is
    quite common. The LM555 is even cheaper and more common, but uses
    more battery power.
     
  5. Here's a two-transistor circuit you could try.

    http://www.terrypin.dial.pipex.com/Images/LEDFlasher2Transistor.gif

    Experiment with the values of C1 and C2 to get the flash rate you
    want.
     
  6. Larry Green

    Larry Green Guest

    Just buy a 'flashing' LED. They are available in a number of colours. You
    will need to calculate the correct series resistor for it though.

    Larry
     
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