LCD problem

[leonel]

I have the following situation...
When my lcd have 4.3V on Vdd it works fine, but when i put 5V at the same Vdd i have all my two lines has on the standard character table FF (the character that corresponds to FF).
My Vdd supports to 6V.
I don´t understand...
What´s the possible problem?
Regards

[NavMicroSystems]

Leonel,

I guess you'll have to adjust the contrast (Vo) for 5v @ Vdd.

See PBP Manual Section 5.37 for an example how to connect a POT to Vo

[leonel]

I already see pbp manual...
But my problem it´s not with contrast, it´s with backlight... I have this configuration

[NavMicroSystems]

...When my lcd have 4.3V on Vdd it works fine,
but when i put 5V at the same Vdd i have all my two lines has on the standard character table FF (the character that corresponds to FF).

...my problem it´s not with contrast, it´s with backlight...

Please be more specific, you are talking about two different things.

[leonel]

i have two different supplies. For exmple +5V for PIC and 4.3V to 74HCT373, 74HCT245 and lcd. When i put all to +5V my lcd doesn´t work.
With configuration fonte1.jpg works and with fonte2.jpg doens´t work...

[mister_e]

What is the purpose of your diode??? isolation of some kind???

Some LCDs will not start bellow 4.5 Volt or so. You have 3 choice...

1. Use a variable voltage regulator set @ 5.7V and this could work with your diodes
2. use a diode in serie between GND pin of your regulator and GND with a resistor to the input... but yuk i don't like that method... even if it's working
3. use 2 voltage regulators

[NavMicroSystems]

When i put all to +5V my lcd doesn´t work.

Come on, be more specific.

What do you mean by "doesn't work" ?
In one post you say there are only black boxes,
in another post you say the problem is with the backlight.

and what is the reason for having 4.3V and 5V as supply voltages?

Have a break re-think your question and be as specific as possible on your next post and we will find a solution.

[BigWumpus]

My suggestions:

Using the 1N4007 in the ground-path of the 7805 will make him to deliver 5,7V on the output. So you should adjust the 5V-Zener-diode !!!! It shortens the ouput of the 7805 !!! Just use maybe 6,3V !!!

Throw away the 1N4007 and use some 1N5818 Shottky-diodes !

[Dwayne]

You say backlight LCD....

Try checking your current drain... How much current are you pulling with everything?

Reason why? I purchased a LCD from electroncs place...connected it up, and almost promptly overloaded my 7805 (which didn't have a heat sink on it). The current drain was 300+ mills just for the LCD!.... Needless to say, I switched LCD's. and only destroyed 2 7805's before I found out what was happening.

Could you be overloading your supply, and the supply shutting down? Can you verify that your 74HCT373, 74HCT245 are working, eventhough the LCD is dead?

Dwayne