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Attenuating video output?

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maxxx

New Member
sed in composite video signal but here is what I am trying to do.

I have a very basic aftermarket LCD screen with composite input (it's the rca-type plug, right?) and an on/off switch, that's pretty much it. My navigation unit is feeding the screen via the composite signal. There are no adjustments for brightness nor contrast, but what I would like to do is to be able to fade the screen to black (or very dim) when desired. For instance, if I am in a dark room, I would rather darken the video image to a point where it is very dim, though visible based on the dark suroundings.

So, I thought of simply putting a variable resistor in line on the composite signal, but then thought it might be more complicated. I am most willing to purchase a pre-fab "box" or circuit of some sort that will allow this continuously variable "fade-toward-black" feature. I imagine there would be some units out there that simply offer the usual contrast, brightness, colour, sharpness, etc. controls, but is there more basically something that might allow the specific feature I am looking for? So far I have searched but not found.

Please let me know what you suggest. Thanks in advance!
 

fernando_g

New Member
Definitively far more complex than a pot.
You need to maintain the proper sync tip and color burst levels, while only attenuating the active video portion above the black level.
 

maxxx

New Member
Good God the aliens have landed. It's like reading the wall of an Egyptian tomb. I've no idea what that illustration means.

Not sure if I should just sloooowly and quietly moonwalk out of this saloon, hoping the locals will turn back to their whiskey, or if I should draw more attention to myself and risk getting blazed for my ignorance... well, here goes...

I was hoping for a little box with a dial.

If there was also a button for ordering pizza, that would be a bonus. (J/K)

Should I get back on my horse and ride out of town? Or is there indeed a simple solution at the end of the fine treasure map that blueroom conjured up? (with many thanks) BTW it looks like a treehouse I tried to build, complete with the front porch and back porch on the same side, and a burst radiator thrown in for anchoring. I see two video parlors, all we need is a pool table, a keg, and a dedicated spot to do #2 and we've got bonafide dojo.

From the most conservative perspective, how many tech college courses away am I from "getting" this?
 

Torben

Well-Known Member
Woah there, cowpoke, don't ride out of town just yet. mneary may have suggested a much simpler way to do it: don't attempt to adjust the signal, but rather, just dim the backlight.

Then again, there is much we don't know about your particular display, so this may or may not be feasible. However, if possible, it would almost certainly be simpler than messing with the actual signal.

Post all the details you can on your LCD display (make, model, link to manufacturer, datasheet, whatever you have) and maybe somebody will have an idea.


Cheers,

Torben
 

gabeNC

Member
Good God the aliens have landed. It's like reading the wall of an Egyptian tomb. I've no idea what that illustration means.

Not sure if I should just sloooowly and quietly moonwalk out of this saloon, hoping the locals will turn back to their whiskey, or if I should draw more attention to myself and risk getting blazed for my ignorance... well, here goes...

Should I get back on my horse and ride out of town? Or is there indeed a simple solution at the end of the fine treasure map that blueroom conjured up? (with many thanks) BTW it looks like a treehouse I tried to build, complete with the front porch and back porch on the same side, and a burst radiator thrown in for anchoring. I see two video parlors, all we need is a pool table, a keg, and a dedicated spot to do #2 and we've got bonafide dojo.

This was hilarious Maxxx!!! Very nice!
You'll find that the locals are helpful 'round here (pssttff... hits the spittoon).
Unless you start flappin yer jaw and shootin' from the hip.
 

maxxx

New Member
Thank y'all, indeed there seem to be mighty helpful folks in these here parts. Special mention for imix500, that there appears to be just what I'm looking for. Much obliged! Now I'm off to lasso some phillies...

(...Clint Eastwood whistling-type music as tumbleweed rolls by...)
 

fernando_g

New Member
If you click open the operation manual for the F2B device that imix500 mentions, you can read the following description:

"The active portion of video is stripped away leaving sync, color burst
and black. The output is dc clamped to zero volts."

So you may see that this is indeed not just a simple potentiometer.
 

maxxx

New Member
Thanks again for your input.

Imix500, can you recommend the least expensive source for an F2B? Thanks in advance.

In the meantime, I'll let the cat out of the proverbial bag: my screen is a 3.5" LCD embedded in a rearview mirror. It is intended for rear-view cameras but it will accept any video source via rca-style video input, and thus I plan to use it for nav. I wish to diminish the screen's output so that I can faintly see the navigation instructions while still being able to see what is behind me.

Following Mneary and Torben's suggestion, I am not sure how to access and apply variable attenuation to the backlight. In any case, is it likely that the backlight should be my principle concern or should I first experiment with a plug-and-play device that fades the signal to "black"? by the way, the standard background for the nav is blue, would the fade-to-black aspect be disfunctional based on this? I doubt it, but need to ask. Thanks in advance.
 

Hero999

Banned

mneary

New Member
[edit]Dimming the backlight should be easy once you find its supply wires. It's likely a watt or two of LEDs, or a fluorescent lamp on an inverter. If you're lucky there's a red wire (I hope it's red) heading towards the backlight area. I would start by seeing what a resistor of 4.7 to 10 ohms 2 watts or so in series would accomplish.

(resistor may get hot)
 
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imix500

Member
Hi maxxx, there are a number of vendors out there for Burst. As you have seen I'm sure, unfortunately anything that says Burst Electronics is expensive. We're actually dealers for them I think. I'll PM you a price tomorrow if you like. Otherwise, I'd look at the usual outlets. Ebay, Gearsource, avforsale, etc.
 

ThermalRunaway

New Member
[edit]Dimming the backlight should be easy once you find its supply wires. It's likely a watt or two of LEDs, or a fluorescent lamp on an inverter. If you're lucky there's a red wire (I hope it's red) heading towards the backlight area. I would start by seeing what a resistor of 4.7 to 10 ohms 2 watts or so in series would accomplish.

(resistor may get hot)
MAXXX: Note that if the backlight is a fluorescent type then you could be dealing with quite high voltages indeed. Make sure you're comfortable with that before you start poking around and messing about with it all.

Brian
 
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maxxx

New Member
Thanks again guys. I now have the fade-to-black module which is very effective, but the backlight remains too prominent for my liking. I will look for someone locally that understands this stuff and encourage the experiment. If anyone can recommend someone in Southern ontario / Waterloo, i would be grateful. Also if you have any more advice I'm happy to hear it! So far been very helpful.
 
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mneary

New Member
Post a photo of the back of the display with the cover removed? Maybe we can spot a backlight control or something. Or maybe some model numbers from the bare LCD or its controller?
 
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