Hi All, I would like to thank to all the people that help me with this,
as most of you said, the way to do that is to invert phase of the
waveform, well I did that and it works, I'm using a 16C84 OTP that
receives via RS232 2400baud the numbers and signs to be displayed, and
the pic generates the AC using TMR0 interrupt, the board remains small
because the PIC is under the LCD display and no other associated IC was
necessary, power used is about 2mA.

Thanks to all of you.
that's a great list.
   Leandro J. Laporta (LU2AOQ)     mail: lu2aoq@yahoo.com
 wrk: Arg. Assoc. for Space Tech.   ham: TCP/IP high speed group HSG


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