I found tutorial about connecting HD44780 display to Raspberry Pi.
In this tutorial there is no contrast potentiometer. Vo is connected to ground.
Tutorial author says:
In order to control the contrast you can adjust the voltage presented to Pin 3. This must be between 0 and 5V. I tied this pin to ground.
Is this common and correct way to use this display?
I never seen that before (Vo connected to GND).
Yes, it works and quite common. It's 0V to VCC, inclusive. Ground is 0V. So that works. You can also use a pair of resistors to make a voltage divider for a fixed contrast outside of just Ground. Only draw back is that you can't adjust the contrast, but unless you are taking the display to very different lighting environments all the time, who cares.
It can be done for some displays. Wide temperature range displays require a negative contrast voltage.
For the narrow temperature range displays, 0V represents maximum contrast, and it may be a bit high even at normal room temperature, but generally if you can adjust the viewing angle, a satisfactory angle can be found.
Personally, I prefer either a microcontroller-adjusted contrast voltage, or a passive automatically temperature-compensation network over either a fixed divider or a potentiometer.
