Jim Dolson <PICLIST@MITVMA.MIT.EDU> wrote:

> I just ordered a DS1669 (PIC controllable pot) to adjust the
> contrast on an LCD panel under PIC control.  I'm always interested
> in reducing the parts count.  How would I adjust the contrast
> using PWM?

    It's pretty simple, Jim:

    1.  Generate a PWM signal.  If your PIC has a hardware PWM
    generator, great... If not, do it in software.  Make the PWM
    frequency as high as possible.

    2.  Integrate the signal with an RC low-pass filter.  You can
    build an op-amp integrator if you like, but it's not really
    necessary... The important thing is to get the filter's 3dB
    point well below your PWM frequency.

    3.  The output from your RC or integrator will be a voltage
    proportional to your PWM signal's duty-cycle; run it to the
    LCD's contrast pin.

    -Andy

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499