strange HD47780 pinout

Hi guys, I have an HD44780-based LCD that I'm trying to hook up to my Arduino Uno, but the pinout seems a bit different. It seems like most panels use a 1x16 pin header, but mine has a 2x7 pin header. I'm guessing the missing 2 pins are for a backlight, which mine lacks. I found the datasheet for the panel, but one pin label confuses me. On the datasheet is lists pin 3 as "VEE", while in the tutorial I'm using it is listed as "V0", which is the variable operating leg of the pot for the backlight (I think). Is this correct? If so, what do I do with the pin? Ground it?

Here's the tutorial I'm using: http://blog.adamsbros.org/2009/06/15/arduino-interfacing-with-the-hd44780-lcd/

Here's the datasheet for the LCD I'm using: http://www.datasheetarchive.com/DMC-24227-datasheet.html

I'm guessing the missing 2 pins are for a backlight, which mine lacks.

You don't have any missing pins. Actually it's the other displays that have two extra pins (for the backlight). The Hitachi LCD interface upon which all else is based uses only 14 pins.

On the datasheet is lists pin 3 as "VEE", while in the tutorial I'm using it is listed as "V0", which is the variable operating leg of the pot for the backlight (I think). Is this correct? If so, what do I do with the pin? Ground it?

Its not for the backlight. Pin 3 is almost always the power for the LCD display itself (as opposed to pin 2 which is the power for the LCD controller). This is the pin that should be driven by the wiper of the potentiometer. Many LCD modules, including many of the Optrex displays that I use, work satisfactorily with this pin grounded although they work better with a slight positive voltage.

Your tutorial is a bit outdated since it does not mention lcd.begin(). This means it was written for a LiquidCrystal library that predates v0017. If you run a later version of LiquidCrystal without that function the library will default to the setup for a one-line display (AARRGGHH).

Your datasheet link points to several similar LCD modules. Unfortunately the differences are in the letters following the the basic part number and those letters often deal with characteristics that may change the voltage required on pin3. Specifically, extended temperature range devices, like some of my Optrex modules, require a negative voltage on pin 3. You will find out if you don't get a row of blocks when you hook up power (pins 1, 2, and 3).

Don

Mine is a 24227-CEM which I couldn't find a datasheet for anywhere. It looks like the pinouts for any 24227 are the same.

My issue seemed to be that I can't for the life of me buy a good 10k pot! I checked the resistance between the V+ and the wiper leg and it was 0 ohms. I don't think that meant the wiper was +5v, I think it's just floating. I wired that pin directly to ground and it worked! I'll keep looking for a pot that actually works, but in the meantime at least it's working!

Thanks for the help!

My issue seemed to be that I can't for the life of me buy a good 10k pot!

The actual overall resistance of the potentiometer is not really that important. Anything between 5K and 25K should be OK. If the resistance is too low then you will be drawing more power from your supply than is desirable. If the resistance is too high you might wind up with some noise issues.

Don

floresta:

My issue seemed to be that I can't for the life of me buy a good 10k pot!

The actual overall resistance of the potentiometer is not really that important. Anything between 5K and 25K should be OK. If the resistance is too low then you will be drawing more power from your supply than is desirable. If the resistance is too high you might wind up with some noise issues.

Don

If you entered your location info in your profile, someone may be able to point you to a local store or online store in your region. BTW, I used as large as 100k but yes noise is big and your contrast will not be easy to stay.