When I was planning to install my MPGuino and put display into an
instrument cluster I wanted to install the smallest LCD I could find. So I bought 53x20mm LCD with enhanced temperature range. After mounting everything I've noticed that contrast is way off the level it should be. So I've started digging and found info that enhanced temperature range LCDs have contrast driven by negative voltage. I hooked up a small battery to provide negative voltage and everything started to look as it should be. But that wasn't the best solution so I decided to build a simple charge pump inverter. It works like a charm.
All you need is a few elements worth less than a soda can.
Schematic diagram:
Parts list:
2x BAT48 - Schottky diodes
2x 2uF - low ESR capacitors
1x 10uF - low ESR capacitor
1x 10k - 0.125W resistor
1x 4k7 - 0.125W resistor
The best thing is that you can still adjust contrast using MPGuino setup screen.