Strange patterns in a LCD touch screen of a Ricoh Aficio 551 digital copier « on: August 08, 2010, 04:45:31 PM » Author: dor123
http://www.youtube.com/watch?v=PX0oBXywPFs I always wondered why the CCFL in the LCD touch screen in this copier of the storage of Carmel hospital, appears to be flickering. So i tried to capture it with my camera in this video to verify that the flickering of the CCFL (And therefore the screen) is a reality and not an illusion and surprised by these strange patterns as you see in the video. What is happening? This isn't a color CRT display, this is a B&W LCD display!
« Last Edit: May 02, 2011, 09:24:42 AM by dor123 »		Logged

I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

I only working with the international date format (dd.mm.yyyy).

I lives in Israel, which is a 220-240V, 50hz country.

	Re: Strange patterns in a LCD touch screen of a Ricoh Aficio 551 digital copier « Reply #2 on: August 09, 2010, 04:52:00 AM » Author: dor123
This copier screen brightness isn't varied by the brightness of the lamp, but by the darkness of the pixels like all B&W LCDs (The lamp remains at the maximum brightness even when the screen is at its minimum brightness [Or maximum darkness]).
« Last Edit: August 09, 2010, 06:04:23 AM by dor123 »		Logged

I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

I only working with the international date format (dd.mm.yyyy).

I lives in Israel, which is a 220-240V, 50hz country.

	Re: Strange patterns in a LCD touch screen of a Ricoh Aficio 551 digital copier « Reply #3 on: August 09, 2010, 02:47:17 PM » Author: Medved
The pixel "darkness" is not constant (mainly on passive matrix displays), but has a ripple originating from the "scanning" excitation (passive matrix) and/or refresh (active matrix displays), what might lead to stroboscopic effect (refresh rate on most LCD's is in 25..60Hz range, so perfect fit with cameras). Passive matrix displays are excited by narrow pulses with altering polarity, active by square-wave. It is, because each pixel need regular excitation voltage reversal to avoid electrolysis destroying electrodes. @Luminaire: The frequency of PWM brightness control is usually 400Hz and above, what usually does not cause the stroboscopic effect with regular cameras anymore.
		Logged

No more selfballasted c***

	Re: Strange patterns in a LCD touch screen of a Ricoh Aficio 551 digital copier « Reply #4 on: August 10, 2010, 12:13:28 PM » Author: dor123
@Medved: Thanks. I don't thought the idea that in passive matrix LCDs, the liquid crystal pixels themselves flickers. I always thought that the lamp in this copier LCD display flickers. In active matrix display usually the pixels don't flickers as my LCD screen of my computer don't shows a flickering at all despite it operates at 60hz refresh rate (Connected to DVI port so 60hz is the only availabe refresh rate).
« Last Edit: August 10, 2010, 12:15:35 PM by dor123 »		Logged

I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

I only working with the international date format (dd.mm.yyyy).

I lives in Israel, which is a 220-240V, 50hz country.

	Re: Strange patterns in a LCD touch screen of a Ricoh Aficio 551 digital copier « Reply #5 on: August 10, 2010, 04:43:55 PM » Author: Medved
On active matrix the flicker is less (as the excitation voltage is present all the time, only swap polarity 60times per second), but still it keep some residue (mainly on panels with faster response time). Sometimes the pixel leakage is high enough to discharge it between voltage refresh events, again on some panels and on higher temperature. The excitation voltage generator source is connected to the pixel only for short time (by the pixel's corresponding transistor) to charge it's capacitance, the rest of the time rely to the capacitance to maintain the excitation voltage. And on higher temperatures, or with worse process the transistor increase it's leakage, discharging the pixel's capacitance, so causing a 60Hz triangle-like waveform of the voltage absolute value, so causing contrast ripple.
« Last Edit: August 10, 2010, 04:59:14 PM by Medved »		Logged

No more selfballasted c***