HD44780 problem

[Marco Trapanese]

Hello

I'm puzzling over my own HD44780 library for Luminary ARM. I ported the
code from a working library I use with AVR.

I see some activity with the oscilloscope and the signals seems ok. The
LCD replies as expected. But I can see nothing on the display.

I remember I should see the pixels on the LCD uninitialized after power
up ii the contrast voltage is good. Actually, I can't see this.

I'm sure the display is working because I removed from another (working)
circuit some time ago.

Do you confirm I should see the pixels when the LCD is powered and not
yet initialized? If so, where should I search the problem? Note I'm
powering the LCD at 3.3V but the datasheet of HD44780 says it's ok.


Thanks!
Marco / iw2nzm

 

[Rich Webb]

Hello

I'm puzzling over my own HD44780 library for Luminary ARM. I ported the
code from a working library I use with AVR.

I see some activity with the oscilloscope and the signals seems ok. The
LCD replies as expected. But I can see nothing on the display.

I remember I should see the pixels on the LCD uninitialized after power
up ii the contrast voltage is good. Actually, I can't see this.

I'm sure the display is working because I removed from another (working)
circuit some time ago.

Do you confirm I should see the pixels when the LCD is powered and not
yet initialized? If so, where should I search the problem? Note I'm
powering the LCD at 3.3V but the datasheet of HD44780 says it's ok.

The HD44780 may be okay with 3.3 V but the LCD module itself may not be.
What voltage is required for (Vdd - Vo) for the module you're using?
It's typically around 4.2 V, so you'd need -0.9 V at Vo to get
sufficient contrast.

 

[Marco Trapanese]

Rich Webb ha scritto:

The HD44780 may be okay with 3.3 V but the LCD module itself may not be.
What voltage is required for (Vdd - Vo) for the module you're using?
It's typically around 4.2 V, so you'd need -0.9 V at Vo to get
sufficient contrast.

Oh! Thank you for the note.
I have a lot of unbranded LCD modules so I haven't their datasheet.
Anyway I try to set a negative voltage on Vo (because all other stuff is
powered at +3.3v).

On the board I have no +5V at all. Do you know any LCD module that works
at +3.3V?

Thanks!
Marco / iw2nzm

 

[Rich Webb]

Rich Webb ha scritto:



Oh! Thank you for the note.
I have a lot of unbranded LCD modules so I haven't their datasheet.
Anyway I try to set a negative voltage on Vo (because all other stuff is
powered at +3.3v).

On the board I have no +5V at all. Do you know any LCD module that works
at +3.3V?

I'm sure there are some but all the ones I've worked with
(purpose-bought for work and "whatevers" surplus units for play) have
been with 5 V on the board.

You might try over at http://www.crystalfontz.com/index.html.

 

[Marco Trapanese]

Rich Webb ha scritto:

I'm sure there are some but all the ones I've worked with
(purpose-bought for work and "whatevers" surplus units for play) have
been with 5 V on the board.

You might try over at http://www.crystalfontz.com/index.html.

Ok, thank you again.

Marco / iw2nzm

 

[[email protected]]

Hello

I'm puzzling over my own HD44780 library for Luminary ARM. I ported the
code from a working library I use with AVR.

I see some activity with the oscilloscope and the signals seems ok. The
LCD replies as expected. But I can see nothing on the display.

I remember I should see the pixels on the LCD uninitialized after power
up ii the contrast voltage is good. Actually, I can't see this.

I'm sure the display is working because I removed from another (working)
circuit some time ago.

Do you confirm I should see the pixels when the LCD is powered and not
yet initialized? If so, where should I search the problem? Note I'm
powering the LCD at 3.3V but the datasheet of HD44780 says it's ok.

Thanks!
Marco / iw2nzm

Your question doesnt make sence. Power up will produce a row of
blocks, initialisation blanks the display, anything else is undefined.

 

[Marco Trapanese]

[email protected] ha scritto:

Your question doesnt make sence. Power up will produce a row of
blocks

Actually, my question asked that. Maybe my English is not so good, but I
was wondering just if the power up produces the row of blocks.

Anyway, Rich Webb found out the problem.

Marco / iw2nzm

 

[Adam S]

Rich Webb ha scritto:

On the board I have no +5V at all. Do you know any LCD module that works
at +3.3V?

If you have a clock source or spare microcontroller pin you can make a
simple negative bias charge pump with a BAV99 dual diode and two ceramic
caps. The LCD drive is about is -4.5V relative to Vdd.