Arduino Forum

Using Arduino => Displays => Topic started by: gregted on Apr 13, 2013, 01:09 am

Title: LCD contrast not working
Post by: gregted on Apr 13, 2013, 01:09 am
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
Title: Re: LCD contrast not working
Post by: marco_c on Apr 13, 2013, 01:14 am
5v on one side, 0v on the other and the center wiper goes to the LCD.
Title: Re: LCD contrast not working
Post by: floresta on Apr 13, 2013, 02:27 am
Quote
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.

Quote
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
Title: Re: LCD contrast not working
Post by: dc42 on Apr 13, 2013, 10:06 am
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.