I have an LCD display that needs -1 volt for contrast. I just used one pin
of the PIC to drive a charge pump - two capacitors, one resistor and a
diode. I didn't need to change the voltage, so I just used a fixed interval
toggling the pin, rather than PWM.  I found that using 10uf capacitors and
a 2.2 k resistor in the filter gave me 1 volt.

At 03:54 PM 2/25/2004 -0600, you wrote:
>Hello I have an LCD stuffed onto a PIC however my problem is definately
>not controling the LCD (pretty easy to do that). My problem is a bit more
>subtle. I don't want to have the expense of a uPot and frustration of the
>fact it's operating range is ussual JUST outside the positive and negative
>voltages from the pic. SO I was think 'Why not use the PIC's PWM' output.
>
>Can one get away with just putting a CAP a resistor ( between the cap and
>PWM drive) N and P type MOSFETs for driving between VEE and VCC? Anything
>I should know? Let me know if this can be done (make my life easier to say
>the least).
>--
>Stephen R. Phillips was here
>
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Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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