Quick LCD question

[Markdem]

Hello,

I have purchased the following LCD,

http://www.futurlec.com/LED/BLUE240X64LCD.shtml

I am a little confused with the power supply requirements. The first part of the specs says that the LCD Driving Voltage is 12v, but then on the pin connection part, it says that it is -10. I know I need to use a pot to control the contrast, but should it be a positive or negative supply??

Thanks

Mark

[vinniewryan]

Judging by the 'Absolute Maximum Ratings' your LCD's supply voltage range is -0.3V to +25.0V, and the typical application supply voltage is +12V, the -10V is a mystery no doubt but there are two other sources which suggest that you'll be safe supplying it with 12V.
_________________
Vinnie Ryan

[PCM programmer]

TC682 Inverting Voltage Doubler: Get -10v from a +5v supply:
http://ww1.microchip.com/downloads/en/DeviceDoc/21453C.pdf

[Markdem]

Hi Vinniewryan,

This is what I thought, but I just want to make sure before I blow up a $70 LCD.

Hi PCM,

I have no problem getting the -10 supply, I am just not too sure if thats what it needs. I have sent a email to the supplier, but knowing them I will not get a very good reply.

Anyone else want to add their .02 ??

Thanks

Mark

[PCM programmer]

Your data sheet says it uses a T6963C controller:
http://www.futurlec.com/LED/BLUE240X64LCD.shtml

Look at the data sheet for a 240x64 LCD from Crystalfontz, that also uses
the T6963C:
http://www.crystalfontz.com/products/24064a/datasheets/249/CFAG24064AFMITZ.pdf

Look at page 8 of the CrystalFontz data sheet. It shows a block diagram
of the LCD. It shows a constrast circuit consisting of a 10K trimpot with
the Vdd voltage (+5v) on the top and the Vee voltage (-10v) on the bottom.

On page 7, it shows the Vee voltage of -10v comes out on pin 9 of the lcd.
On this particular LCD, it generates the Vee voltage for you. But your
LCD does not do this. You have to generate it with an external circuit.

Here's a forum that discusses your question in detail, with a photo of
the LCD and the contrast voltage required to make it work correctly:
http://www.lcdstudio.com/forum/viewtopic.php?t=10919

They talk about a quicky circuit with two 9v batteries to make a -18v
contrast voltage (for a trimpot). The following schematic shows how
to do it:
http://www.aasi.net/development/datasheets/LCD_VFD/t6963tst.gif

[Markdem]

Thanks PCM,

It has been confirmed that the LCD indeed does need a -10 rail. I will just use a charge pump from a faulty LCD i have sitting around.
I just wish this website had some proper data sheets.

Thanks

Mark

[bkamen]

Most of the time, you really don't need the -10V... A lot of LCD's are visible at room temp at 0V contrast. BUUUTTTTtt...

If you are using a MAX232 somewhere for serial ports in your circuit, you can borrow some of the -10 it generates off the V- pin.

(fun)

Otherwise, building at least a -5supply is easy with something like a MAX829 style inverter or an ICL7660 (if I'm remembering the part numbers right).

You don't need a lot of current, As PCM mentioned, it's just a bias thing for LCD contrast.

-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D