'Overclocking' LCDs. Any ill effects?

[Al Borowski]

Hi all,

I'm working on a device with a low resolution, monochrome LCD (it
appears to be "4-bit dual scan display mode (STN)"). I'm trying to get
greyscale working properly at the moment. The LCD controller has
hardware greyscale built in, but enabling it shows a fair amount of
flicker in some shades, even with hardware dithering.

If I increase the clock to the LCD controller by about 40%, this flicker
basically disappears. Will problems will this cause in the long term?
Could it damage the LCD?

thanks,

Al

 

[Al Borowski]

I should mention: This is for a device which I have very little
technical data. While the SoC is standard, the LCD isn't, and I know
nothing about it.

So, just as an educated guess, am I asking for trouble by increasing the
clock rate over what the manufacturer is currently using?

cheers,

Al

 

[Bill Sloman]

I should mention: This is for a device which I have very little
technical data. While the SoC is standard, the LCD isn't, and I know
nothing about it.

So, just as an educated guess, am I asking for trouble by increasing the
clock rate over what the manufacturer is currently using?

Probably not, in the sense of permanently damaging anything. The clock
rate of an LCD is (or used to be - it is a few years since I knew much
about them) limited by the speed at which the molecules in the liquid
crystal line themselves up with the changed electric field.

The only risk you might be running is that the display will stop
following the controlling field at low temperatures, when the
viscosity of the liquid crystal material is higher.

Higher clock rates do imply more capacitative current flowing through
the tin oxide connections on the glass enclosing the liquid, but this
ought not to be significant.

Just my educated guess ...

 

[Tim Shoppa]

Hi all,

I'm working on a device with a low resolution, monochrome LCD (it
appears to be "4-bit dual scan display mode (STN)"). I'm trying to get
greyscale working properly at the moment. The LCD controller has
hardware greyscale built in, but enabling it shows a fair amount of
flicker in some shades, even with hardware dithering.

IMHO if you see it flickering in grayscale pixels, it's because the
dithering frequency is beating with the multiplexing frequency. This is a
design flaw IMHO, the two clocks should be chosen to never fall close
to each other (or the important divided-down freqs).

If I increase the clock to the LCD controller by about 40%, this flicker
basically disappears. Will problems will this cause in the long term?
Could it damage the LCD?

If you see it flickering because of beating between the two clock rates,
then the flickering pixels may have some short-term (well, over the time
between flickers) DC bias on them, which
is a not-so-good thing for LCD's. If you get rid of the flickering by tweaking
clocks, then you're probably getting rid of the DC bias, and that's a good
thing.

Tim.

 

[Al Borowski]

thanks for the replies.

cheers,

Al