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Use an LED monitor as a lamp - faking a VGA signal? Answered

I have an LED monitor with a smashed screen that I'd like to repurpose as a light panel. The backlight still works (driven from the onboard controller) but cuts out after 20 seconds or so.

I assume this is because the board fails to sense a connected source (it has VGA and HDMI inputs) cable and switches to standby. Is there a simple way of "fooling" the monitor that there's a source conencetd so that it remains lit?

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Jack A Lopez
Jack A Lopez

11 months ago

I recently noticed there exist vga test signal generator boards, and there exist various video converters (e.g hdmi to vga converters) with vga output.

Both of these are sold by, what I will refer to broadly as, the Chinese eBay sellers.

I mean the way that works is, you ask eBay to show you some thing you suspect exists, like maybe a "vga signal tester"

https://www.ebay.com/sch/i.html?_nkw=vga+signal+tester&_sop=15

And this will produce a list of dozens of, almost identical, circuit board looking things.

Then you ask it to sort that list by, "Price+Shipping: lowest first"

Often if helps if you can guess at the same title words being used by the sellers, and it might take a few iterations to see which words these sellers are using.

I do not know how familiar you are with the Chinese eBay market. The best thing about these sellers are they supplying things that are novel (i.e. items that cannot be found anywhere else) and they are usually very cheap. There are some drawbacks though, including: Monte Carlo build quality, minimal or zero documentation (i.e. instructions, wiring diagrams, etc), and the little board takes several weeks to arrive in the mail.

However, I think this plan would work; i.e. (1) Buy a little board that makes vga test signal. (2) Figure out how to supply power to it. (3) Connect it to your monitor's vga port.

This is not exactly a "clean hack" in the sense that we have to do complicated things (i.e. make a complicated signal, using purchased hardware) in order to do simple things (i.e. make a light turn on).

However it might be a "cheap hack" in that the board that makes that signal should cost less than 10 USD (more than that is too much, at the time of this writing). Also it might be cheap in comparison to the labor required to do it the clean way; i.e. diving into the existing electronics on the monitor, and finding a way to force the power to the backlight to stay on.

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Yonatan24
Yonatan24

11 months ago

I'm assuming you saw this on the DIY perks Youtube channel, but if not, I think he may have come up with a solution for this in one of his videos.

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Jack A Lopez
Jack A Lopez

Reply 11 months ago

For anyone wondering at the method for this one, skip to about 7m+40s.

where Mr DIY Perks replaces the existing line of white LEDs, with the same length of white LED strip light.

Also there might have been a clue would happen, in the video's description, since it includes an affiliate link to ScAmazon, preceded by the words, "Here are the LED strips I recommend"


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Jack A Lopez
Jack A Lopez

11 months ago

I found some clues, the most important of which is an answer at quora-dot-com, to a similar question, by someone named, "Andrew Silverman"

Quote:

"In VGA devices that support the VESA DPMS (Display Power Management
Signalling) protocol, different combinations of turning off the vertical
sync clock, horizontal sync clock, or both are used to tell the monitor
what level of “sleep” it should go into. The spec was designed at a
time when CRT monitors were the dominant technology and had significant
warm-up time, so multiple levels of power management were supported.
With the advent of backlit LCD monitors, there’s little need for more
than one level of power-down any more and no common operating system
ever provided more than a single on/off control anyway."

link:
https://www.quora.com/What-15-pin-VGA-carries-wake...

Also the pinouts of a 15-pin VGA cable are widely published. Even Wikipedia has a good overview, here:

https://en.wikipedia.org/wiki/VGA_connector

Anyway, my guess is the presence of a signal resembling vertical sync clock, which is the slowest of these signals, circa 60 Hz or 75 Hz, would be enough to fool the monitor into staying on. Although this is really kind of a wild ass guess on my part.

https://javiervalcarce.eu/html/vga-signal-format-t...

Fortunately there is a way to test this hypothesis. If you have an old computer, with VGA port, to produce all the signals that are part of the VGA protocol, and if you have a sort of homemade vga breakout box, that is some way to disconnect most, but not all, of the pins. Then you can try running the monitor with just one signal connected at a time.

I think for just the vertical sync clock, that is going to be only pins 10 (ground for VSync) and 14 (VSync) connected, according to the table I am looking at, on the right side of the Wikipedia article for "VGA connector."

Edit: I just noticed the Wikipedia article for "VESA Display Power Management Signaling"
https://en.wikipedia.org/wiki/VESA_Display_Power_M...

and there is a table there that suggests both the VSync clock and HSync clock need to be present to indicate the monitor should be 100% powered on.

By the way, there might be an easier way to do this, if you can discover more about your monitor. I mean if there were a way to, like, see into its heart, or brain, or sense organs, and find this organ that is watching the VGA line, and then sending a signal to shut everything down. You know, if you could find that signal, and it was an easy signal to mess with, then that would be the easier way.

Also I noticed this link too,

https://electronics.stackexchange.com/questions/23...

which is someone else asking a similar question, but maybe with the twist that he wants to command the monitor to display a totally white screen.

If that kind of fakery is understood, perhaps totally red, blue, green screens are possible as well, and that is sort of where the answers given to his forum topic, seem to be pointing.

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Henmarsh
Henmarsh

Reply 11 months ago

Thanks for those comprehensive references Jack - I appreciate the time you took to dig them out. I'll work through the links you give. As the actual TFT layer of the screen has been removed and only the LED backlight remains, I won't need (or indeed be able to!) drive the actual display at all. I don't have an oscilloscope (or indeed the knowledge to use one properly). I'd really like to use the built-in driver for the LEDs - it amazes me how such a simple re-purposing of broken displays into light sources hasn't been more widely documented!

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Orngrimm
Orngrimm

11 months ago

"active" does not mean white. An active VGA-screen is black... unless you send analog data
to it to make it anything different than black.
White is a signal which has to be generated...
https://www.instructables.com/id/Arduino-Basic-PC-... maybe?
https://simple-circuit.com/interfacing-arduino-vga... is another option
https://forum.arduino.cc/index.php?topic=102181.0 is as well another option
or https://forum.arduino.cc/index.php?topic=320238.0
or https://hackaday.com/2014/06/10/640x480-vga-on-an-...

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Henmarsh
Henmarsh

Reply 11 months ago

Thanks for the response. The display screen itself has been removed; all I need to do is to keep the backlight on.

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Downunder35m
Downunder35m

11 months ago

Not really.
Easiest way I know would be to fool the power supply and add a PWM control for the backlight.
But if it is still working you can measure the voltage supplied to the LED's.
With that info you can use a normal LED driver to power them.

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evamajlak
evamajlak

11 months ago

This is interesting and impressive at the same time if it works.