LCD - blue text instead of white

[futz]

I have a bunch of these LCDs from DipMicro.

They display white text on blue background. Well... until now they did. Since I started using the display on the Unicorn and using 8-bit mode (Bill Blueroom's code and my own) it now displays dark blue on blue - almost unreadable. And I have no idea why.

I did get it to display white on blue a few times while I was still porting my code from the 4-bit Junebug original code, but things weren't working right yet and all it displayed was gibberish. But at least it was nice white gibberish.

Anybody know what I'm doing wrong?

 

[blueroomelectronics]

Does text or gibberish appear on the display, Is the backlight running? Is the Unicorn jumper installed?
Try the basic program in the Christmas section.

 

[picbits]

Sounds like a contrast problem.

 

[OY2L]

The backlight must always be on on blue lcd's otherwise the letters is almost black.

 

[futz]

Does text or gibberish appear on the display,

Text. Looks perfect, but dark.

Is the backlight running? Is the Unicorn jumper installed?

Yes and yes.

Try the basic program in the Christmas section.

Same results.

The backlight must always be on on blue lcd's otherwise the letters is almost black.

I'm thinking saggy power maybe. Tho strangely it was running on the same power when I got normal white text for a bit there. I swapped in another LCD and things stayed the same.

Or contrast... Hmm...

 

[mvs sarma]

It is no doubt contrast. there is no back with this display. background is blue. characters have to be white, gradually turn buleish, still darker blue to the extent that you see (for eg case of alpha-numeric displays the 5x7 matrix meant for the character will fully become dark and so you see dark rectangles) dark characters.

Merry Christmas to all

 

[futz]

It is no doubt contrast.

I really think you might be correct. I gotta go to work now, but I'm going to hit that as soon as I get home. Will post the results. Thanks.

 

[futz]

Got it cured. It was saggy power, as I had guessed (which indirectly becomes a contrast problem). I was powering the Unicorn off the programming cable from my Inchworm+ and another Unicorn, all powered by the USB cable in the programmer Unicorn. Guess I found out how much is too much for that thing to put out.

Oh ya, Bill, the 10K trimpot on the Unicorn is fine for contrast, as you said. 20K would give more adjustment room. 25K probably not necessary.

EDIT: The LCD that wouldn't even start up before works fine now too. Guess it was more particular about its power than the blue ones.

 

[blueroomelectronics]

You can power the Inchworm+ from its power jack while it's connected to the Unicorn USB, plenty of power for the LCD and won't hurt your USB port.
20K is from the GLCD datasheet, but 10K is fine too.

 

[futz]

You can power the Inchworm+ from its power jack while it's connected to the Unicorn USB, plenty of power for the LCD and won't hurt your USB port.

That's exactly what I did. Problem solved.

 

[blueroomelectronics]

Now if I could only figure out how to modify the Junebugs hex file to request 500ma from the USB.

 

[futz]

Now if I could only figure out how to modify the Junebugs hex file to request 500ma from the USB.

Now that would be a very welcome update!

 

[Pommie]

Now if I could only figure out how to modify the Junebugs hex file to request 500ma from the USB.

You would be one very smart cookie if you managed that.

Mike.

 

[blueroomelectronics]

It's probably only one byte but which one...