How to control the contrast of a HD44780 display (Arduino)

To control the contrast of a HD44780 I am using a 10K Ohm Poti to be able to adjust the resitance a little bid.

Sometimes I had the problem, when I was using a fixed resistor for the contrast with 1K Ohm, that the contrast was not perfect.

The advantage of the poti is that you are able to change it in a small range. (For example to make the squares disappear)

Just put one pin of the poti to VCC and the other to GND.

Then connect the Output to the 3rd pin of the HD44780 display and you are able to adjust the contrast.