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LCD contrast issue? Answered

Just got a LCD 20X4 character screen. 10K pot connected to 5V. Can controll contrast. problem is, only 1/2 of it???


only 2/4 rows of character blocks go dark when full contrast. why is this!!!



10 years ago

I dunno, not enough info...

--Link to the data sheet?
--Check your connections?

--Are you actually displaying chars, are you just biasing up the background?

Sometimes rows respond differently, but only when the contrast is adjust WAY out of useful range, so what would normally be clear (the background) darkens...

And yep, I've "bricked" one, too. Hope that's not the case..

Well when i did that, i only had the +, -, and contrast connected. A 10K pot, so i can go from nothing to pitch black. but like i said, only 2/4 rows go black. But i'll see if i can get a datasheet. I only got a Pin layout from the company.


It seems like it's a series. I searched the BOLYMIN and the model name, BC2004A. I will tell you it has 3 micro chips under it (covered in black circles) KS0066 built-in controllers. So yeah, Biasing up the background.


I wouldn't sweat that. If the KS0066 controller and driver are there, it's all you need. That could be a spot for an on-board power regulator, or something.... If it was a custom part, it could be anything.

If you use one of the examples we discussed before (LCD drivers), it will work--assuming everything is setup right. A quick search for KS0066 returns info like:

Here is brief data for the Systronix 20x4 character LCD. It is a DataVision part and uses the Samsung KS0066 LCD controller. It's a clone of the Hitachi HD44780. We're not aware of any incompatibilities between the two - at least we have never seen any in all the code and custom applications we have done....

So any standard char LCD AVR driver will work.

I would address the contrast issue after you get the LCD working. You'll never get the contrast right until you've got characters displaying on the scrn...

Re: the device #-- BC2004AYPLEH$

Page 4 of the BC2004A series PDF has info to decode that part #. It looks to be what you'd expect.

Only the last code char ($) is missing-- it's the "Special Code." That may be an instance of: xxx=to be assigned on data sheet.

But sometimes they don't provide data sheets, especially if it was a custom part...