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LCD Monitor mod Backlight

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Newbie level 4
Apr 29, 2011
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So, I have successfully converted my broken iMac G5 into a computer monitor with a DVI input, the only problem is that when the computer puts the display to sleep, the backlight stays on. Is there a circuit i could build or buy that will sense the video signal from the computer and turn off the backlight when required, monitors you can buy do this but I don't know how they achieve it.


thank you in advance.

First of all you measure the voltages of video signal when you have some display on your LCD then measure voltages when your computer is on sleep mode & noted down all measurement. Use Op-Amp as voltage comparator to compare video signal voltage & o/p of voltage comparator fed to a transistor which is actually a switch to turn off or on your LCD backlight.

I was thinking the same thing but I measured the voltages beginning with a display on the screen, and holding it until the display sleeps. Before sleep I measured 4.98 VDC and after sleep it went up to 4.99 VDC. It was the same amount of difference on all wires, just different voltages, but they all went up by only 0.01 volts. Is that enough for a comparator?

If the situation is that then this option should be discarded.
Is there a CRO is available to you? If so then try find out signal change when sleep mode is on & off.
I think this isn't voltage level this may be signal from PC which drive LCD to sleep mode.
Good Luck.

I don't have a CRO, so I don't know how i would go about it. But it must be a very minute signal from the PC that I just can't pick up with a multimeter. I may research digital video signals a little more to learn more about them. If not, I'll scrap the idea and just turn the monitor off manually when I leave the comp.

If CRO is not available to you then I think nothing you can do in this moment but to turn off monitor manually.

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