Change viewing direction + improve contrast of most GLCDs and HD44780-compatible LCDs

nick12ab

Senior Member
LCDs (such as that sold by Rev-Ed) have poor viewing angles (this isn't Rev-Ed's fault) and manufacturers compensate for this by 'biasing' the LCD so that the viewing angle range is not centered and it looks better either from above or below. It also doesn't look that good when viewed from the unintended angle, even with the magnitude of the contrast voltage (negative relative to Vdd) increased to compensate.

Additionally contrast can be negatively impacted by... the colour of the backlight! If your LCD has a white backlight then skip to the end to read about that.

Viewing Angle

Of course, you could just use an OLED display but those aren't really suitable for use outdoor in bright sunlight and will use more power than a non-backlit LCD.

Whilst you can usually find out the 'view direction' from the datasheet before buying the LCD, you cannot always find this out (Rev-Ed don't tell you what the view direction for the LCD included with the AXE033/AXE133 is) and you might only be able to obtain the LCD in the colour and size you want in one viewing angle from a particular supplier. If you don't have the desired viewing direction then it will not look very good at all. The shadow formed by the dots in particular can look odd. Getting the view direction right is particularly important for GLCDs as they have pretty bad contrast to start off with.

But all this usually doesn't matter because this can be changed on most LCDs (including HD44780-compatible character displays and KS0108B-compatible graphc displays). Simply take the panel out and put it back in the other way round!

Before doing that, you should determine whether it can actually be done.
  1. Inspect the elastomeric connectors without removing the bezel and make sure that they are both elastomeric connectors - if one is just a plastic/rubber support then there are only connections on one edge of the panel and therefore the panel cannot be put in the other way up. It also means that all the connections will be much closer together so if you do remove the bezel it will take a lot of fiddling to line up the connectors again to get it to work again.
  2. Make sure that the elements on the display panel are symmetrical. Turn up the contrast after initializing the display and if your display looks like this then this will probably work:



    But if it looks like this then it may still work but there will be a gap between the top row of pixels and the rest of the character (yes I tried it):



    If it has symbols on it, then don't bother. Otherwise you'll end up with this:


Once you've checked that, use pliers to straighten the bezel retainers and remove the LCD panel and bezel from the PCB. Depending on the LCD module, the bezel might have a rectangular hole in only one end so the end of the LCD with the lump on it will have to go at that end, or it will have rectangular holes at both ends but only one end will allow it to fit over the backlight, or it can fit both ways.

View attachment 13774

Reassemble the LCD with the LCD panel backwards (top at bottom, not front facing back), refit the bezel and bend the tabs on the back. Be careful with the alignment of the LCD panel particularly with GLCDs where there are more small contacts. Reconnect the LCD module to the test circuit and make sure that it works. If part of the display does not work, straighten the nearest tab to the offending area on the bezel then bend it again while holding the bezel in and bending the tab towards the PCB.

Depending on the size of the original bias angle of the display, you'll notice either an insignificant or significant improvement. Either way there will be an improvement.

View attachment 13775

The bottom display in the comparison above is after the view direction has been corrected. It is a bit better, but the difference doesn't show much in the photo. The scratch on the display has moved to the other end of the display which clearly shows that this is real and that this isn't a guide to destroying your LCD. This particular LCD didn't have a big 'bias angle' anyway - the effect with other LCDs was greater.

The LCD in the comparison below had a more significant improvement and it is the same size as those used by Rev-Ed, with the pins at the bottom. The backlight didn't actually change colour. The display at the top is before and the display at the bottom is after. If you look carefully, you can see that a mark by the top left corner of the '0' in the middle of the top line is now on the bottom line in the lower display. More significantly, the text is a bit blacker and the inactive pixels are no longer visible.



LCDs that worked:
  • The AZ Displays module supplied by Rev-Ed with the AXE033
  • DEM 16215 SYH-LY (large module - pictured above - effect not that great)
  • DEM 16217 SYH-LY-CYR22 ('Rev-Ed' size module - pictured above - more significant improvement)
  • Fordata KS0108B-compatible GLCD which was once sold by Rev-Ed (significant improvement)
LCDs that didn't work:
  • WH1602L-NYG-JT (large Winstar display, did work except for gap between first and second row of pixels for each character so small 'Rev-Ed size' Winstar LCD should work)
  • Powertip backlit LCD supplied with AXE033B - didn't work because it only has a connector on one edge of the LCD so it cannot be inserted the other way round.
  • AMPY 2001-11 - for obvious reason!
So basically all the displays that didn't work didn't have to be attempted at all since in both cases this blog entry could 'diagnose' the inability to do this with no disassembly involved.

If this blog entry does not indicate that it can't be done on your LCD, then it will probably work. I'm sure that manufacturers design the panels so that all the pixels will be correctly connected when upside down deliberately so that they only have to make one LCD panel to suit both viewing directions and they can choose the viewing direction by choosing which way to put the panel in.

Backlight Colour

Poor choice of backlight colour can result in inferior contrast. The most common poor choice for monochrome displays is white (which is commonly used with 'negative' LCDs) due to most LCDs not being suitable for use with a blue backlight. Cold white LEDs emit a lot of blue light, along with the other colours required to produce white light. This particularly affects GLCDs which are already at a disadvantage due to their low duty cycle for each row scanned.

Most white backlights consist of a small number of 3mm white LEDs inserted into holes in a thick sheet of plastic. To test your LCD, remove them and fit one (or more) blue LEDs and attempt to use the LCD. Alternatively the design of the backlight might provide a point that you can hold the LED in front of and it will light the LCD, which will eliminate the need to desolder anything for testing. You should find that the result is quite terrible. This applies not only to the common white on blue variety of GLCD, but also others including black on white/green GLCDs and character LCDs.

The solution is to replace the white LEDs with LEDs of a single colour (amber works well) and this should result in a significant improvement in contrast quality. Bright LEDs are required as there is usually only opportunity to fit two LEDs and the white LEDs they are replacing are very bright. If you really need to keep a white backlight, then some improvement can be made by using warm white LEDs.
 

Buzby

Senior Member
Hi nick,

What is the difference between doing all that hacking, as opposed to just mounting the whole thing upside down ?
 

nick12ab

Senior Member
Buzby;bt319 said:
What is the difference between doing all that hacking, as opposed to just mounting the whole thing upside down ?
If you mount the whole thing upside down all the text on the HD44780-compatible LCD will be upside down or with a GLCD all the addressing would be reversed.

Changing which way up the LCD panel itself is does not change the orientation of whatever is being displayed relative to the PCB.
 

Buzby

Senior Member
Hi nick,

I must have been having a senior moment, I completely forgot they are character displays !.

A project I did in the past used a 128x64 GLCD rotated 90' to get the right row/col aspect needed, so I just thought another 90' would fix your problem.

Anyway, it was good reading you pointed to. I learnt a few new things about LCDs I didn't know before.

Cheers,

Buzby
 
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