Problem driving a laser pointer


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  1. #1

    Default Problem driving a laser pointer

    Hi,

    As a beginner, I am trying to drive a laser pointer from a PIC16F84 using this simple program:

    -----------
    loop: High 0 'Turn on LED connected to RB0
    Pause 1000 'Delay for 1 second

    Low 0 'Turn off LED connected to RB0
    Pause 500 'Delay for 0,5 seconds

    GoTo loop 'Go back to loop and blink LED forever
    End
    ----------

    For sure it flashes but it looses much brightness.

    I tried to drive the laser pointer from a TIL111
    using the following circuit but it still looses much brightness.

    http://www3.sympatico.ca/louiscimon/...9v%2016f84.pdf

    I suppose that "High" is in fact an oscillation that is not a continuously "on".

    I have the same difficulty trying to drive a piezzo buzzer
    (Velleman SV10) : it looses much loudness in the process, even driving it from 18 v
    with the TIL111.

    I would like to understand and find a solution.

    Thank you very much

    Louis Cimon
    Québec, QC
    Canada
    http://www3.sympatico.ca/louiscimon/

  2. #2
    Join Date
    Mar 2006
    Location
    China
    Posts
    266

    Default Pin 6?

    Hi,

    Are you sure the TIL is fully open? 4.7k as the LED resistor seems a bit much.

    Bring out your DMM and measure the voltage on the TIL to see what is happening.
    /me
    Last edited by Jumper; - 2nd June 2008 at 03:02.

  3. #3

    Default Problem driving a laser pointer

    Hi Jumper,

    Thank you for your input.

    I changed the resistor for a 470 ohm.

    I am reading 4,92 v between rb0 and ground
    and 4,92 v between TIL111 pin 1 and ground

    I am reading 8,35v between TIL 5 and battery and the battery produces 8,35 v.

    I tested my piezzo on two 9v batteries in series and the sound output is greatly reduced when I drive it with the TIL111 compared to driving it directly with the batteries. The voltage readings of the batteries and the TIL11 output are the same.

    Solution?

  4. #4
    Join Date
    Mar 2006
    Location
    China
    Posts
    266

    Default There are better drivers

    Hi,

    Why do you want to use this optocoupler? If you just want to switch something on with the PIC I would go for a FET solution.

    ULN2001 is a favorite at this forum and if you only want to handle up to 500 mA this will do fine.. IF you need more you can use more channels in this chip in parallell.

    You can also try to measure the current thru the laser to compare it with and without the TIL.

    /me

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