If it's a home project, and you've got voltage headroom from your power
source, then the simplest way is to insert two diodes in series (and a cap)
from your circuit ground point back to the battery - . You now have a
reference point at -1.2V

Regards
Roland


At 07:59 PM 25/02/04 -0500, you wrote:
>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
>>
>>--
>>http://www.piclist.com hint: To leave the PICList
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>
>Larry Bradley
>Orleans (Ottawa), Ontario, CANADA
>
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>
Regards
Roland

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