Cheap LED array

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Cheap LED array

Postby Andrew Davie » Fri Dec 08, 2017 11:02 am

I thought this would be of interest to the group. I purchased some 12V LED flat panels from AliExpress, with a view to using them to backlight lithophanes. They arrived today - all of $0.77 each with free shipping. AliExpress is extremely reliable; I have bought several hundred things through the site. The video shows they're plenty bright enough, even for use with thick lithophanes. To my eye it's more diffused than the video shows, so not such a glaring bright spot. But still very bright, so that's fantastic. Very pleased with these, so here's the link...

AliExpress 12V LED panel

OK, so yes that's me in the lithophane. I also thought these panels might be useful to those making a televisor, as they're really cheap, about the right size, and although not extremely bright, I'd classify them as very bright, too bright to look at directly. Worth considering.

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Re: Cheap LED array

Postby Andrew Davie » Mon Dec 11, 2017 2:39 pm

led.jpg
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Thermal imager after 1 hour of operation at 12 V shows maximum temperature just under 70 C.
The array was pulling 170 mA.
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Re: Cheap LED array

Postby smeezekitty » Tue Dec 26, 2017 3:48 pm

Andrew Davie wrote:OK, so yes that's me in the lithophane. I also thought these panels might be useful to those making a televisor, as they're really cheap, about the right size, and although not extremely bright, I'd classify them as very bright, too bright to look at directly. Worth considering.


I question if they are both fast enough and controllable enough for that. LED modules with built in current regulators might be quite slow to respond and won't might not dim linearly.
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Re: Cheap LED array

Postby Klaas Robers » Fri Dec 29, 2017 9:54 pm

LEDs on their own are fast enough. If there is a built in current regulator, remove it. It is the video output transistor that should regulate the current, nothing else. Another problem might be that the LEDs are circuited in series, to run them on 230V AC or 120 V AC. It might be difficult to split that up into shorter series that will run on a more practical DC voltage, with the video output transistor in series of course.

But if they are cheap, buy one, open it and see what you find inside......
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Re: Cheap LED array

Postby Harry Dalek » Sat Dec 30, 2017 7:54 am

If they are in series and you have now removed the regulator or bypassed it and found the diodes are wired in series you could still modulate them in a way similar to the singing arc circuit .....a 555 oscillator run at 30 or 40 khz ...audio modulate to pin 5 pin 3 to a power transistor it to a step up transformer to the voltage needed...need a small one a few ohms primary and a few k's secondary ..finding the right transformer is harder ...same circuit has worked on a rotary transformer ,singing arc flyback transformer ,induction coil modulation all the same idea just feeding to a different coil or transformer of some sort....
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Re: Cheap LED array

Postby smeezekitty » Sat Dec 30, 2017 8:22 am

It's not a mains voltage lamp. It's 12VDC so modulation shouldn't be a problem at all. Without a current regulator, the forward voltage is probably in the 10-11V range.
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Re: Cheap LED array

Postby Andrew Davie » Sat Dec 30, 2017 11:37 am

I just need to find some time to put it in my televisor. It's a direct drop-in voltage and wiring-wise. If it works, good and well. If not, then I won't bother with it.
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Re: Cheap LED array

Postby Andrew Davie » Sat Dec 30, 2017 3:49 pm

Here are the results. It works. I think it might be switching slower, as I detect a slight banding/pattern in the picture. Hard to tell. This taken in daylight, and the brightness is a tad down on my bespoke light so it's a bit harder to see. But in short it does work and would be an OK starting point for someone building a televisor like mine.

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Re: Cheap LED array

Postby Harry Dalek » Sat Dec 30, 2017 4:45 pm

Doing well Andrew if you are still using a regulator .can't say i ever got any laser diode or diode array to work with a regulator connected do you see any caps on the circuit as that would not be good ? interesting but !
Last edited by Harry Dalek on Sat Dec 30, 2017 6:04 pm, edited 1 time in total.
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Re: Cheap LED array

Postby Andrew Davie » Sat Dec 30, 2017 5:52 pm

I tried dissecting one of the units, but didn't really get far. The foam backing tape came off, leaving a bare metal plate. The front yellow "stuff" appeared to be a sort of foam covering that easily picked off with my thumbnail. I exposed a couple of rows of what was underneath. When I tried applying power, those rows no longer worked, but the rest still did. Very odd. Couldn't see any components at all other than what is shown in the pictures.

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Re: Cheap LED array

Postby Harry Dalek » Sat Dec 30, 2017 6:10 pm

I can't see any regulator for it ..to me looking it looks clean circuit diode array ..did you check if the foam stuff has resistance it might be part of the circuit ? if not i am not sure why some of the diodes have stopped ..perhaps that backing is a big resistor if you have a multimeter i would be interested either way .
Fascinating dissection ~!
Last edited by Harry Dalek on Sat Dec 30, 2017 6:14 pm, edited 1 time in total.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Cheap LED array

Postby Andrew Davie » Sat Dec 30, 2017 6:14 pm

Harry Dalek wrote:I can't see any regulator for it ..to me looking it looks clean circuit diode array ..did you check if the foam stuff has resistance it might be part of the circuit ? if not i am not sure why some of the diodes have stopped ..perhaps that backing is a big resistor if you have a multimeter i would be interested either way .


I'll send you a couple to play with. Shoot me an address via PM.
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Re: Cheap LED array

Postby McGee2021 » Sat Dec 30, 2017 6:17 pm

I suspect that the yellow covering is a functioning part of the LED's, and thats why the uncovered ones stopped working. Maybe its like the plastic sheath on two pin LED's? Break the glass on an incandescent bulb, and the filament can work. Take the covering off and LED, and the chemicals coating the anode and cathode oxidize, making it useless. its very strange thats its so weak you are able to pick it off with your fingernails.
John Logie Baird was obviously the man who sowed the seeds but did not reap the harvest.
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Re: Cheap LED array

Postby smeezekitty » Sun Dec 31, 2017 5:53 am

The "yellow stuff" contains phosphor. The underlying diode is monochromic blue/violet which excites the phosphor reemitting white. That's how most full spectrum LEDs work.

It's also clear that when you took the phosphor coating off, you broke the bond wires. It's a thin piece of wire that goes from the terminal to the left of each diode die up and over connecting to the top of it.
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Re: Cheap LED array

Postby Harry Dalek » Thu Jan 18, 2018 9:58 pm

Sorry for the delay Andrew but so far what i have found is the yellow jell its self has no resistance i agree with the last post its a form of phosphor that is charged by the led array .
Doing a UV light test on the jell it emits white light so i would say the array is a bunch of UV leads charging the phosphor in the jell.
I can see the jell has a white barrier around it ,must be stopping a transparent film of something they don't want to dry out that is connecting leds
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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