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

[NavMicroSystems]

Allow some time for leonel to come back with some more details.

Or do you want to continue providing solutions he has got to find a matching problem to?

[leonel]

I'm back
My problem it´s that:
In the beginning of my project i had a problem wiht backlight but now it works putting My Vcc at +5V.
My ideia of putting two diodos at the end of my regulator it´s having my PIC with one isullated suplly, and the rest of my circuit with one different suplly. I'll have one independent +5V to the PIC...
If i put PIC, LCD, 373 with the same suplly it works, but if i put PIC, LCD, 373 and 245, this is all circuit with my output regulator it doesn´t work.
This morning i'll try doing more tests then at the end of the day i'll tell you more thinks...

Note: sometimes i don´t say too much because i don´t write very well in english.

[Melanie]

I've either been up too long, or in desperate need of some more coffee... just misread "two diodos " as something completely different!

As long as you have a common 0v, it shouldn't matter how many different supplies you have. Are you overloading your Regulator? When everything is connected (and not working) what is the +V on each device?

[leonel]

This morning i put 2 regulators, but the problem still happens.
I thing that i´m not overloading my regulator. I'm using 7805 that supports 1A.
With this morning tests i think that my problem it´s with my 74HCT245. And why? When i put 4.3V on my 74HCT245 i don´t have problems in the display. I see the datasheet and there´s a diference between 74HCT245 and 74HC245. For HC the condition is VI = GND to VCC For HCT the condition is VI = GND to VCC - 1.5 V. What´s this meaning? That i cannot put Vcc to +5V or my inputs/outputs have to be 5-1.5=3.5V????

Melanie said:
When everything is connected (and not working) what is the +V on each device?

In each device i have +4.9V.

[leonel]

As i said i'm giving more news...
I changed my 74HCT245 to 74HC245 and i have no problems... I don´t understand very well but it works!
Now i only have one problem
My MCLR has the circuit attached, but when i close my circuit almost the time doens't do the reset. But if i put my multimeter between pins 1 (MCLR-Vpp) and ground, to measure my voltage it works fine...
What probably it's happening??
What can i do?

Sorry to have strange questions and strange problems, but i'm new in this matter and i like to understand the problems.

[Dave]

leonel, With the diode in the direction that it is the Processor will never reset with the pushbutton. What is the reason for the diodes direction?

Dave Purola
N8NTA

[leonel]

In datasheet of 18F458 pag 23 section 3.0 (Reset) there´s a schematic. I did a little changes to use a switch and make a reset through a switch... It´s not the first time i'm using this circuit and in the others have been working!

[mister_e]

I still prefer the KISS engineering... but it's my own opinion.

how about something like that
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=394&stc=1">
you can remove the toggle switch...

In fact to do ICSP i use the above in conjunction with a simple ICSP switcher like that
<img src=http://www.picbasic.co.uk/forum/attachment.php?attachmentid=163">
This allow me to do everything for developpement without install/remove the ICSP connector.

[Acetronics2]

Hi, leonel

Try a Schottky diode ( BAT 85 i.e. ) or Germanium diode ( OA ...) instead of the 1N4148 ... its leakage current will make your reset circuit work better !!!

that's not very elegant ...but will work !!!

Alain

[leonel]

What i did and it works was putting a R=100K between pin 1 and ground, in conjunction with my circuit.
What's the "KISS engineering"?

[mister_e]

Well a pull;-down should be bellow 10K and will affect your current design.

KISS engineering... not meant to be ofendant by any way...of course
Keep It Simply Stupid Engineering.

That's my favorite method.

[Acetronics2]

Everything that avoids a floating pin condition works ....

as Ralf wrote : RTFM !!! ( for humour here ... but found at page 9 or 10 !!! )

Alain