texy wrote:I,ve played with many LCD's over the years, and nevered needed a negative rails for the contrast. A pot between 0v and Vcc set to a voltage inbetween will do the job.
It depends on whether the LCD is a text mode or a graphical display, both have very similar interface, and shape, but often graphical types needs a negative contrast voltage, while normal text mode LCD's do not.
Just to muddy the waters, I have come across HD44780 based Alphanumeric / Text LCD displays which DID require a below-zero contrast voltage on the contrast pin in order to achieve correct contrast and did typically require the use of something like a 7660 IC to generate the negative voltage.
However, all such displays that I have seen were from the first generation onto the market, typically with light grey backgrounds and fairly poor character contrast even when optimally adjusted.
All the newer ones I have seen (typically with green backgrounds) have worked with a contrast voltage in the range between V+ and 0V, usually somewhere just above - in fact you can usually just strap the contrast pin to 0V and they will work, albeit with the contrast a little on the strong side.