After noticing just such discussion last month about using the PWM
module on a PIC to adjust LCD contrast, I designed a program to do
just that.  The problem is that the voltage output from the PWM
through my RC filter only works properly on the oscilloscope.  There,
it cycles nicely from 0 to 5v (although I get the impression that the
upper ranges are largely useless).  However, when I connect it to my
LCD module (run by a Hitachi whatever-it-is), it only goes from 2v to
5v, leaving the displayed characters largely invisible throughout the
range.

The filter I am using is just an RC filter.  I thought that since I
want 0-5v, I could leave the op-amp off my integrator.  Am I wrong?

I guess this is more an electronics question than a PIC question;
perhaps somebody could advise me whether this is [OT] or not.

-tom

p.s. I have consulted what I believe are all the relevant Microchip
PWM AN's, but I still wonder why I can't leave off the op-amp.

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tomss at ids.net - 401-861-2831 - 42 Forge Rd, Potowomut, RI 02818 USA