Converting 5v LCDs to 3.3v and tweaking a MakeCode extension

RE: Converting 5v LCDs to 3.3v and tweaking a MakeCode extension

svdp — Fri, 06 Nov 2020 15:26:15 GMT

Hi Hugo,

I think there is a difference between the blue and the green lcd screens. For the blue LCD's and active pixel is transparent and a background pixel opaque. The back light is seen through the transparent (active) pixel. For the green LCD it is just the other way around the active pixel is opaque and shows as "black" both require a different contrast voltage. So the points I want to make are:

-hack does not work for a green display

-value of R6 is not justified, if you take 0 Ohm its also fine for a blue display

-no distinction made between display types

Yes, you can you a pot but the proper values for R6/R7 are also handy ;-)

Kind regards,

Stefan

RE: Converting 5v LCDs to 3.3v and tweaking a MakeCode extension

svdp — Fri, 06 Nov 2020 14:41:32 GMT

Hi Steve,

The patch you suggest does not work for a green display. The reason is quite obvious. The output of the charge pump is connected via voltage R6/R7 to Vo.

You just take 2.2k for R6 without any reasoning which means that the full -3.3V is on Vo. Which leads to way too much contrast.

RE: Converting 5v LCDs to 3.3v and tweaking a MakeCode extension

Jan Cumps — Sat, 15 Jun 2019 22:26:47 GMT

I’m running that type of display on 3v3 without translation. They use a popular Hitachi compatible driver that functions with 3v3 on the data lines. I’ve driven them from a TI Hercules and an Intel embedded controller. Only the background led needs a little more umph. I’ve published a C driver for both on github.

RE: Converting 5v LCDs to 3.3v and tweaking a MakeCode extension

neilk — Sat, 15 Jun 2019 15:14:28 GMT

Hi Steve

Nice mod to the display board and I like the custom block for MakeCode.

Neil

RE: Converting 5v LCDs to 3.3v and tweaking a MakeCode extension

shabaz — Sat, 15 Jun 2019 11:54:36 GMT

Hi Steve,

Great info! I've been meaning to do the exact same mod with some 16x2 screens, and purchased the bits but not got around to it yet.

Nice to see the mod will work.