Control audio volume, LCD contrast, frequency, etc. by using two buttons instead of a common potentiometer. This circuit explains how we do it with Maxim’s DS1669 IC. This IC is very popular and is widely used because it is a potentiometer that never wears down.
By using S1 and S2 pushbuttons you can adjust the resistance. C1 is only a 0.1uF ceramic capacitor. You can use the datasheet of DS1669 to get more detailed information.