Increasing 20x4 LCD contrast range

Jun 29, 2021 5 Replies
B

Replaced the LCD and backlight assembly in my old Emu ESI-4000 sampler:


Which after 25 years even the LED back lighting was starting to get annoyingly dim.



Replaced it with one of these white-on-black units which works fine and looks pretty good:


Except that the software-adjustable contrast range, which was probably optimal for a black-on-yellow display, can't bring the CV up enough to avoid some "blockies" shining through. I'm wondering if there's a quick hack to get some more range. Or maybe it would be better to put a resistor in line with the backlight supply to reduce bleed-thru.



The "Turbo" board on these adds some of the nicest digital filters there were in a hardware sampler of the era:



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B

Yeah. It's a little difficult to capture this particular color scheme correctly on a cell phone camera but at the maximum range of the control it looks kinda like this:

And unfortunately the contrast is controlled in software, probably via PWM there's no direct connection to an analog adjustment pot.

I might swap it for an OLED display instead, or just go back to the boring black on greenish-yellow. Hmpf.

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B

I got pic of it by turning off the HDR on my camera, it looks about like this at the maximum excursion of the contrast control. A lil worse in the pic than it does in person.

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R

Okay, I use the blue modules with the pot turned back until the blocks are only a little darker than the background which isn't too bad.

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R

There still will be some line with a varying voltage that doesn't do anything else, and which you can try to pull up or down using a resistor.

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