[chbot] Blue HD44780 LCDs

[Helmut Walle]

Good point - and you can turn a negative pixel display (active pixels 
bright on dark background) into a positive one (active pixels dark on 
bright background) by rotating one of the polarising filters (if there 
are more than one anyway) by 90 degrees. Now as most displays are not 
square, how do you that...? Well, if the polarisation plane of the 
filter is at 45 degrees to the edges of the filter then flipping it 
either horizontally or vertically is optically equivalent to rotating by 
90 degrees. If the plane is parallel to the edge you're out of luck...

DISCLAIMER: I just made this up as I was going and don't have time to 
check and confirm that it is correct in detail, but the key point is 
that these displays all work on the physical basis that the LC affects 
the polarisation of light passing through it. So they all have 
polarising filters to make the differences in polarisation of the light 
visible to the human eye (which is not polarisation-sensitive). The 
filter is a thin sheet of plastic that just looks grey to the eye. 
Disassemble a module, take the front filter out, and experiment with 
turning and flipping it with the display on...

Kind regards,

Helmut.

On 11/08/15 00:33, m.beckett at amuri.net wrote:
>
> Robin
>
> My observation of the Blue background LCD's is that they are inverse 
> of the Yellow ones. ie the pixel is clear or see through rather than 
> blocking.
>
> They tend to ghost more, and hence you need to scroll them slower.
>
> Mark
>
>
[...]