You not satisfied with the ordinary LCD modules, but you can’t find what you’re looking for? If you still want to fit the whole thing into a box with a footprint about the size of a deck of cards, then you should consider using Optrex DMC-16207 modules, where they’re using the Hitachi chipset.

Your goal for this project is to write a nice library module/class that encompasses these different approaches and present a clean interface to the programmer to select the options.

For your information, the Arduino is getting power from USB, where it supplies 5v power to the LCD. The LCD contrast is already hard-wired to ground. If you want to adjust the contrast, then you can apply a potentiometer into the project. You can use bench power supply to run the LED circuit at 9V.

By the way, the easiest thing to do here if you don’t have a method built is to apply the pushbuttons to bump the desired voltage up and down. It will be even more fun, if you can do it with a spinny-wheel.

Lastly, remember to have fun with the project!