EEVblog #898 - LCD Contrast Experiments

What is the difference between LCD viewing angle and bias angle?
How does adjusting the LCD bias voltage effect the display?
What is LCD Ghosting?
Also a demonstration of Photoelastic Birefringence in polycarbonate plastic display covers.
Dave investigates the Liquid Crystal Display viewing angle problem in the EEVblog BM235 Multimeter.

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[WamWooWam]

I like how rather than posting on your forums or just ignoring it, I'd someone complains or something breaks you make a really interesting video looking in to it. This is what I call customer service. Valve, take notes.

[rwbishop]

I always liked how HP makes the viewing angle adjustable on most (or maybe all) all of their LCD calculators. With the calculator on, you press and hold the 'on' key, then adjust using the '+' or '-' key to suit your prefs... it only takes a second and can be done on the fly to match different environmental conditions.

[robfenwitch]

DaveCAD has overlays! Is this a V2.0 preview?

[KennethLavrsen]

The strange rainbow colours when looking through a polarized filter is also a problem when looking through polarized sunglasses. It is the plastic window in front of the LCD that does it. Often these windows are made from polycarbonate and it is ultrasonic welded to the housing. It is the ultrasonic welding that creates tensions which makes the light rotate. Normally you cannot see that but with LCD in combination with polarized sunglasses you get the problem.

[Ts]

The color patterns you get on some of the multimeters when looking through the polarizer is caused by strain set up in the transparent plastic(used for the cover protecting the screen) during manufacture. I believe the phenomena is called photo-elastic anisotropy/birefringence or something like that.

[oriole]

The combination of forum feedback and the ability to respond directly through these videos puts you in a pretty unique position to develop and refine some kick-ass products with maximum customer satisfaction haha. ;) Great video and great explanation!!

[simonsventroschke]

Normally you CAN remove the original filter. Its just a glued-on foil on top of the display. Its visible in your video, too, because the filter foil is always a little bit smaller then the glass. If you remove it and put on a filter at 90° different then the old one, you have a negative (inverted) display.

[kaizen]

Who knew a video on contrast could be so interesting. Thumbs up for the diagram as well. Always very handy for numpties like me.

[Seegalgalguntijak]

Thanks for explaining this! I knew about the polarizing filter, but I never knew about the bias angle. Now I've understood something that I've been noticing since I took apart LCDs as a kid in the 80s!

[NRBW]

Cool, DaveCad now supports more than one layer

[AlainHubert]

All DMMs should have an adjustable contrast level. It's not that hard, nor costly to implement. The Fluke 115 (that I have) also suffers from a poor contrast when viewed from above eye level.

[raincloudnz]

Re: rainbow colors when viewed through polarizing filter. What you are seeing is the birefringence of the plastic cover which is above the front polarizer of the LCD. The key determinates of the birefringence are the plastic itself and the internal stresses in the plastic.

[djslaviero]

Hey Dave, can you change the warranty info to void if not modified? :)
Other than that small issue, great meter!

[DoRC]

I noticed that when you had the LCD out of the meter and had forgotten to take the filter off your camera it was behaving like the other ones in that the screen was blanking out entirely.

[leighmoom]

I bought this meter from you and havent had any issues. It is a 2nd meter so not always used. Great video to point it out. I have a fluro mounted 800mm above bench. Have used the meter when I am sitting and standing and never had an issue reading it with my old eyes. Hence reason for the light just above the bench.

[joe]

Dave, you must be in the guiness world records for having the largest multimeter collection in the world. How many do you actually have?

[contemporiser]

There are different kinds of polarizing filters, most of them are linear, newer displays tend to use circular filters more often, they allow much wider viewing angle, I suppose.

[violentsense]

Nice video. I wonder - can I adjust the bias angle of my Fluke 87V. Because the screen looks blurry, when I look straight at it.

[BobbieBees]

Which is why LCDs should be replaced with the ever popular Flip-disc displays.

[someperson]

It's a shame Brymen didn't make this adjustable, either through a software setting or at least a trimpot on the board. But I really appreciate the effort you put in to investigating the issue and making a video about it, just like you did with the broken component last time. I think I know where I'm going to buy my next multimeter :)