LCD Partially Working


New member

I have this LCD screen ::

At 3V its works fine. Text displays perfectly. BUT the contrast is VERY low, text is next to invisible to see.

I put power up to 4.5V and the contrast is great! But the text wont display correctly all comes out in $$$$$ signs and solid blocks, Ican see parts of texts flying accross the screen. but its not readable at all.

It cant be a wiring problem because it works at 3v just no contrast...

Can anyone think what is up?

P.S. The backlight IS working.
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CF Tech

Try this circuit, which has been floating about the web for some time:

You basically need a limiting resistor on your backlight, a potentiometer on Vo and grounds from the parallel port to the LCD at a minimum.

The potentiometer will allow you to change the contrast setting without changing the LCD's logic voltage.

Read this thread for instructions on how to do the backlight limiting resistor.


New member

im not all that good with electronics... but how will adding a limiting resistor fix the garbled information on being displayed on my LCD?



New member
Ok its been a while thought id bumpm the thread and add some more info...

On the back there is like 5 chips one is the HD44780 but it says HD44780A00

anyone know if this LCD is even workable lol ?