LCD contrast not working

Hi all.
I have got my LCD 12864 working ( finaly read the part of the instructions that said put 12 k resistor between gnd and lcd ) with my arduino UNO except the contrast pot does nothing.
I have tried pin 8 on one side of pot with pin 3 on center and ground on other side.
I have tried pin 3 on one side of pot with pin 8 on center and ground on other side.

I know the pot works as I used it for brightness control on this same setup.

It's not a biggy but would be much clearer with contrast.

Great forum btw

Greg

5v on one side, 0v on the other and the center wiper goes to the LCD.

5v on one side, 0v on the other and the center wiper goes to the LCD.

Not for most graphical LCDs.

5v or 0v on one side, -18 (approx) volts on the other side, and the center wiper goes to the LCD. You can typically get the negative voltage from the device itself, usually pin 18.

I have tried pin 8 on one side of pot with pin 3 on center and ground on other side.
I have tried pin 3 on one side of pot with pin 8 on center and ground on other side.

So - assuming you meant pin 18 instead of pin 8 then option 1 should work and option 2 could burn out the potentiometer and/or the negative power supply.

Don

Post a photo of the back of your LCD. Some of them don't have the contrast pot pin connected, and they either have a tiny pot on the board itself or a fixed resistor. If yours is legible with no contrast pot connected, then I suspect it is one of these.