Cheap way to generate the negative supply, two capacitors, 2 diodes,
using any clock or repetitive high frequency pulses. You can isolate it
if necessary using any 74HC gate to feed the C1 capacitor.
The output (without load) is equal to -Vcc + voltage drop across both diodes.

              ;        C1           k
_-_ o------||-----+------|<------+-------o output -Vdc
                   ¦             |
        82pF    & nbsp; V             --- 1nF
                  ---            ---
                   ¦ k           |
                  ---            ---
                 ////           ////

On Tue, 23 Feb 1999, Kevin Cantrell wrote:

> I bought 5 and am happy with them. The have a standard Hitachi 44780
> controller. The 22-pin connector is a little funny, but they supply the
> pinouts. The part only has data bits 4 through 7, so you are limited to
> four bit mode. The contrast is OK with pin 16 at 0 V, but I can't seem to
> increase it. I think I may need a negative suppy.
>
> Kevin