Pulse Width Modulation (PWM)

Started Aug 18, 2013 | Discussions
Thomas Niemann Veteran Member • Posts: 4,451
Pulse Width Modulation (PWM)

An interesting article on PWM was published at TFT Central. Click on Testing and Interpretation and you'll find a simple technique to determine the frequency of backlight modulation.

I performed this test on my Dell u2412 monitor with brightness cranked down to zero.

Taken at 1/125th I can see 4 vertical bars on the right and barely see 4 bars on the left. That's a total of 8 bars * 125 = 1kHZ for backlight frequency. At this frequency screen flicker should not be a problem. Indeed this is the case for my setup.

If you have a monitor that employs PWM, what is the backlight frequency for your monitor?

Greg.
Greg. Senior Member • Posts: 1,236
Square waves rule...

Hi Thomas.

PWM controllers are wonderful devices, and as I am sure you already know, their use today in the world of electronics is many and varied.

I will conduct the monitor test during the coming week.

Regards, Greg.

OP Thomas Niemann Veteran Member • Posts: 4,451
Different versions of Dell u2412

Well, it appears there is more than one version of the Dell u2412 monitor. Mine behaves like this , while a post at youtube from 2 years back behaves like this. Mine is stamped version A00 made in China.

NewsyL
NewsyL Veteran Member • Posts: 5,751
Re: Different versions of Dell u2412

Thomas Niemann wrote:

Well, it appears there is more than one version of the Dell u2412 monitor. Mine behaves like this , while a post at youtube from 2 years back behaves like this. Mine is stamped version A00 made in China.

Mine is a Rev A02.

Using my Samsung phone for the video, it looks like yours.  No flicker, clear screen.

Using my DSLR for the video, horizontal bars form on the screen and change thickness and darkness as the brightness is changed.  But they don't move, they are static in position.

It would seem to me that the hardware used to video the screen has an influence on what is captured in video.

.

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OP Thomas Niemann Veteran Member • Posts: 4,451
Re: Different versions of Dell u2412

NewsyL wrote:

Using my DSLR for the video, horizontal bars form on the screen and change thickness and darkness as the brightness is changed. But they don't move, they are static in position.

Since they remain in the same position, are the horizontal bars visible with the naked eye? If not, I'm thinking it might be some type of interference pattern (moiré) between the pixels on your monitor and your screen.

Pictus
Pictus Veteran Member • Posts: 6,572
Re: Pulse Width Modulation (PWM)
OP Thomas Niemann Veteran Member • Posts: 4,451
Re: Pulse Width Modulation (PWM)

Pictus wrote:

http://youtu.be/ru474L8N15w

Another 2-year old video. Mine, which I purchased last week, shows no scrolling horizontal bars or stroboscopic effect. I'm wondering if they have tweaked the monitor a bit since then.

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