Which LED driver?

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Which LED driver?

Postby ylagandre » Thu Jul 17, 2014 5:11 am

Hello,

I am a novice when it comes to electronics but would very much like to build a mechanical television for an art project. I signed up for the NBTV newsletter and am looking at the boards for sale. On the website it states there is an LED driver that will support up to 40 LEDs. Which of the two designs will power the most LEDs? The Klaas Robers or Peter Smith?
I plan to drive and sync the motor with an arduino and only require a board to drive the LEDs. Any guidance would be appreciated.

Thanks,
Yann
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Re: Which LED driver?

Postby Harry Dalek » Thu Jul 17, 2014 9:08 pm

ylagandre wrote:Hello,

I am a novice when it comes to electronics but would very much like to build a mechanical television for an art project. I signed up for the NBTV newsletter and am looking at the boards for sale. On the website it states there is an LED driver that will support up to 40 LEDs. Which of the two designs will power the most LEDs? The Klaas Robers or Peter Smith?
I plan to drive and sync the motor with an arduino and only require a board to drive the LEDs. Any guidance would be appreciated.

Thanks,
Yann



You can go pulse width modulation too ,theres a bit on past posts on driving leds .
Also you'd do better with Luxeon or star leds they give more light and you don't need as many .
I would review past posts but i don't recall any one needing to drive 40 leds is it a Nipkow or a simple matrix type thing ?
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: Which LED driver?

Postby ylagandre » Fri Jul 18, 2014 2:09 pm

I don't remember where I read 40 LEDs. That must be a mistake on my part. I should mention that after I make a small prototype I would like to scale the disc up to a four foot diameter disc. I'm not sure how many LEDs I'll need for that but I'm sure it'll be a lot.
Do the boards in the NBTV newsletter come with a BOM? Or do I need the issue of the newsletter in which it was published?
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Re: Which LED driver?

Postby ylagandre » Fri Jul 18, 2014 2:10 pm

Oh and I believe I will be making a Nipkow disc.
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Re: Which LED driver?

Postby Panrock » Mon Jul 21, 2014 4:57 am

Steve Anderson designed a very good wide-band LED driver that would support around 65 LEDs. I used three of these with my colour mirror screw.

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Re: Which LED driver?

Postby Steve Anderson » Mon Jul 21, 2014 6:47 pm

Ylagandre - I admire your vision but I suggest you take it one bite at a time. There are few except the likes of Baird who have got anywhere near a 4' (1.2m) disc. And then (correct me if I'm wrong) he had to run it in a vacuum otherwise air resistance was a major obstacle. But maybe that was due to the drag presented by the lens-disc array...though this I believe was a camera rather than a display device. Others, please input here...

The electronics today is easy, the mechanics is not going to be. Even using the standard 12.5fps rate with a 4' disc - work out the outer edge speed. It's the same sort of limitation on placed propeller aircraft, but a bit less so. Around 172km/hr...as my reckoning is. Others please check my maths...that's a lot of drag. You're going to need an industrial motor of a few HP for that - then how to control it.

Start small, then work up, just as the pioneers did.

Steve A.

Those of an inquisitive nature...work out the propeller tip-speed of a Piper Cherokee aircraft (a four-seater puddle-jumper) with a propeller of 72" (6 feet diameter) at an PRM of 2500 cuising at 110 knots... how close is the tip speed to the speed of sound? You'll be surprised. No wonder the Spitfire, Hurricane and US P-51 had real problems in this area...as do all prop aircraft, even today. Don't forget the forward motion makes the trace through the air a helix.
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Re: Which LED driver?

Postby ylagandre » Tue Jul 22, 2014 5:50 am

Steve O. and Mr. Anderson, thank you for your input and advice. I was planning on getting a rather large motor and then controlling it via pulse width modulation from an arduino with the aid of this product: http://www.powerswitchtail.com/Pages/ZeroCrossTail.aspx. It allows an arduino to control an AC current. Just plug it between the wall and the motor and the arduino would synchronize the televisor with the same program written to synch the smaller televisor. You say I will run into problems of drag though... Is there a way around this? Other than sealing the televisor in a vacuum of course!

Cheers,
Yann
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Re: Which LED driver?

Postby Steve Anderson » Tue Jul 22, 2014 4:06 pm

I think I have a duty, nay obligation, to dissuade you from pursuing your goal of a 4' (1.2m) disc. It is simply too dangerous when constructed in the usual fashion in a home & hobby environment. This thing, should it lose its main attachment to the drive-shaft or the bearings fail will potentially slice you in two. This thing would need to be finely balanced otherwise it will simply tear itself and other components apart.

DON'T DO IT.

You have been warned!

I reguarly mess around with lethal voltages that many would not even wish to be present in the same room. But (I like to think) I know what I'm doing. After almost 59 years I'm still here. Much to the chagrin of others at times.

Ask Steve O (aka Panrock) about balance on his mirror-screw monitor which has dimensions far less than 4'.

Can you explain how this would fit into "an art project."

Steve A.
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Re: Which LED driver?

Postby ylagandre » Tue Jul 22, 2014 5:42 pm

I understand your concern and thank you for your sage advice. I am a novice after all; however, I would not be altogether alone in this venture. I would construct this project at a local maker space where I would consult with people far more experienced than myself in making mechanical things. Dave Dalton, the owner of this maker space, has designed and constructed factory robotics among many other things. I would consult him before attempting anything. I have another friend who is a mechanical engineer with whom I would also consult.
OK, how this fits into an art project:
I'm doing a project on the murders that have occurred in my city—especially those committed against people under the age of 18. I live in the United States, where gun violence is a pervasive problem. I want to interview people who have known, in some way or another, children who have suffered violent and intentional deaths.
The reason I want to use a baird televisor is the way it so transparently reveals the phenomenon of persistence of vision. It is an aesthetic choice with conceptual underpinnings. These children who are the subject of my project are like invisible citizens of our world—I insist that their presence is still relevant to our world. The image quality of a baird televisor strikes me as ghostly and I believe it is the most appropriate means to display the interviews.
The viewer who sees the testimony of people who have known children who have died by murder on a baird televisor will be witnesses to moving images that reveal something invisible about the world. Is this not what a mechanical television does? Does it not render something you would not see otherwise? This is what moving images mean to me.
So why do I want it so big? Well, it's a formal decision. I suppose I could build a smaller one if I must; although, I far prefer a large image. The televisor will be on view in a gallery. I fear that a small image will be lost in a large space. Also, I just want to do something different.
Please forgive me if my message is at all long winded or convoluted by art speak. I have a bachelors in fine arts and not a degree in electrical or mechanical engineering.
I understand that this project is beyond my personal skill set, but I am determined to do my subject matter justice. I intend to make models before going large scale and I will consult with the most knowledgeable and experienced people I know to see it through.

All the best,
Yann
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Re: Which LED driver?

Postby Steve Anderson » Tue Jul 22, 2014 9:08 pm

ylagandre wrote:I understand your concern.. I would consult him (others, Edit SA) before attempting anything. I have another friend who is a mechanical engineer with whom I would also consult.


Well, my previous post still stands, but please consult these individuals, all I can hope is they'll agree. But then again...

If it's the persistance of vision you're thinking of there's always a device like Alberts 'Niptrix' which for all intents and purposes recreates the flickering image you seek with no moving parts - and at NBTV resolution. It is not an insigificant undertaking however. It also generates a frame larger than a 4' disc could ever do. Don't forget a 4' disc rotating at 750 RPM is NOT going to be quiet. A museum/gallery/exhibition will most unlikely tolerate that...and add to that the motor noise.

If it were the UK the Health and Safety Executive would have it shut down in no time. Mostly I don't agree with them, but here...

I suggest you really think this through thouroughly, as an impoverished artist it's gonna cost a lot.

Please, I do not intend to seem negative about this, just is it practical?

Steve A.

How's your theory on Phase-Locked-Loops by the way?

And I have to ask what is your source material? And how do you propose to convert it to a NBTV format? And while we're on the subject matter, how are you proposing to replay it?

I admit, when it comes to art I'm a Luddite.
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Re: Which LED driver?

Postby Lawnboy » Tue Jul 22, 2014 10:26 pm

Yann, I would second Steve A.'s recommendation about starting with a smaller disc first. The larger discs can be very finicky given their inertia (not to mention dangerous if you accidentally bump into one at speed.) A few years ago the club sold a 19" aluminum disc and it took me months to get the thing to sync reliably, although I was using a DC motor.
You are correct that Klaas' driver can in fact drive 40 LEDs in series if fed with 100 vdc, but you will need a separate power supply to do it. I would go with Peter Smith's design personally as it can be easily modified to provide up to 1400ma of current without the use of high voltage. One final point worth mentioning is that brighter does not necessarily mean better. With the low frame rate of NBTV flicker is very apparent and the brighter the picture the worse it becomes. A tiny, dim image in a darkened room is much easier on the eyes (and stomach) than a large, bright image in a well-lit room.


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Re: Which LED driver?

Postby Harry Dalek » Tue Jul 22, 2014 10:38 pm

There is also other ways to get a lager picture size such as Steve has mentioned one ,the one very interesting thing about mechanical television is theres lots of ways to end up with the same result ...some easier than others .
The Nipkow is of cause the easiest and the most elegant .
Theres lots of different designs apart from a Nipkow ,but never making one it is more than likely your best option .
I would listen to Steve about the size of the project you are trying ,if any thing try it small it may be all thats needed ? if you have enough light you can do lots .
get as large a lens as you can track down increase image size with that
You could go PWM laser..... projection..... small disk cd size a defocused laser circle to the size of your disk raster ,size of the first and last hole and a lens and project to a screen.
Still lots of problems to make it work but if you have the will...
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: Which LED driver?

Postby ylagandre » Wed Jul 23, 2014 5:46 am

Hmmm… I had not considered the noise issue. That and all the other points mentioned are dissuading me from making this so big. This reality check was well worth my effort! Thank you everyone for chiming in.
What if I just used a fresnel lens on a regular sized Nipkow? Fresnel lens come in large sizes. Does anyone foresee any problems of using a fresnel lens as large as 6"x6". What about 1' x 1'?

Cheers,
Yann
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Re: Which LED driver?

Postby Harry Dalek » Wed Jul 23, 2014 4:12 pm

ylagandre wrote:Hmmm… I had not considered the noise issue. That and all the other points mentioned are dissuading me from making this so big. This reality check was well worth my effort! Thank you everyone for chiming in.
What if I just used a fresnel lens on a regular sized Nipkow? Fresnel lens come in large sizes. Does anyone foresee any problems of using a fresnel lens as large as 6"x6". What about 1' x 1'?

Cheers,
Yann


I have only ever used optically clear lens perhaps you might not need a diffuser if you use one others may know ,try a laser pointer behind it ,may show your the size of a raster dot would be at different distances and what a sweep line would be like .
My first monitor i used a large magnifying glass ,i don't know if you can find one but the old Photographic 35mm enlarger can have a very large lens or 2 .
You might like to work out a plan to make your device like now working out the image size .
Your idea of a large image is good but going in a easier direction you can have the same result .
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: Which LED driver?

Postby holtzman » Sat Jul 26, 2014 7:58 am

It's an interesting project and I do think the larger is the disc, the better, in terms of the artistic impact it would have on a viewer. Actually it was my dream to make some art project with NBTV, with a huge nipkow disc... But instead I built smaller devices with double speed feature - twice large image. They can be seen here on this forum and on my youtube channel.
http://youtu.be/ToJuNt7eM6c?list=UUqPjAdWW8LqpVSUMfUyXdEg
http://youtu.be/EXpA9HNiyHg?list=UUqPjAdWW8LqpVSUMfUyXdEg
http://youtu.be/v8l8Tfoto94?list=UUqPjAdWW8LqpVSUMfUyXdEg
Don't expect too much from magnifying glass. I experimented a lot and found it disappointing. Frensel is even worse than regular. The main reason is that viewing angle through the lens is very narrow, you need to be just in front of it. Those special magnifiers for early CRT tv were with a very short focal lens. And magnifying glasses are usually with long, or very long in Frensel, focal lens. Wish you best luck!
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