Typically tft lcds displays use a large negative voltage in that range
(-10 to -20 volts dc), but nearly every character LCD I've seen uses an
lcd voltage of 0 to -5 volts, with -3 volts being a good starting point.

You won't damage the lcd by starting out at 0 and going up to find a
good contrast level.  It uses so little current that you could use a
nine volt battery and a potentiometer, positive to ground and one end of
the pot, negative to the other end of the pot, and the center (moving
point) going to the vlcd.  Use a largish pot (1k - 100k).  It's useful
for testing.  If that doesn't work, use two nine volt batteries.  Of
course, a power supply would be good, but the nine volts are
automatically current limited if you should short something out.

-Adam

michael brown wrote:

>Oops, this time with a topic tag.  Sorry
>
>I have googled myself blue, but I can't seem to find a decent application
>note for "putting the juice" to this display.  At US$40.00 each I would
>prefer not to boil the substrate, so I need some clarification on the LCD
>contrast voltage.  The data-sheet that I found shows the supply voltage for
>the contrast pin as Vdd-Vee 18.5 to 19.5 volts.  I am fairly sure that the
>contrast "really" uses a negative voltage.  Are they trying to say that Vdd
>*minus* Vee should be in this range 18.5 to 19.5 volts.  So by my
>calculations this works out to be 5V - (-14V) = 19V.  So I think that my
>contrast voltage should be in the range of  -13.5V to -14.5V  Does this
>sound correct to everyone???  The really interesting part of the data-sheet
>is in the Absolute Maximums box.  It plainly says that the maximum Vdd - Vee
>is 2480V, is this for real????
>
>This display uses a "cold cathode" type bulb for the back light.  I made it
>light up today and didn't even let any smoke out.  ;-D  I used a little
>12VDC to High-Voltage AC.  I'm not sure exactly what the voltage is when the
>backlight is lit, but I my meter says 810V.  Is my relatively cheap digital
>volt meter lying to me?  Since the AC voltage is being supplied from a
>converter, I assume it is at a high frequency (like maybe in 50Khz
>range???).  Would this make my volt meter reading way off since the AC is
>not at 60Hz?  800V seems a little optimistic for this tiny little converter.
>The converter is made to run beautifully colored "cold cathode" bulbs, but
>the bulbs I have seen used are probably twice the length.  They now have
>some shorter "colorized" bulbs and are recommending the same converter for
>them.  I am just worried that I am going to burn out the back light with
>extended usage.  The datasheet specifies a nominal voltage of 300Vrms and a
>max of 350V.  The absolute max is 1500V.  Should I be looking for (or
>building) another converter?  Help me, please, before I elexamacute myself
>or worse.  ;-)
>
>--
>Michael Brown
>Instant Net Solutions
>www.KillerPCs.net
>
>"In the land of the blind, he who has one eye is king"
>
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