NBTV without any moving parts. THE NIPTRIX

Forum for discussion of narrow-bandwidth mechanical television

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Postby Klaas Robers » Tue Oct 09, 2012 4:37 am

I know at least that the LEDs in a TV remote control run at about 1A when they are on. However they run at a mean duty cycle of 1/80, so the mean current is still no more than 12 mA. So if you leave the LEDs time to cool down, they can be overdriven considerably if you do that for a short time.

So if you plan to have one NBTV-line on for 1/32 of a frame, that is 1/400 sec, then you may run it at a peak white current of 500 mA per LED. For 48 LEDs in one line that is 24A from your power supply (as there is always a line in operation) for a white frame.

But then you will see the flicker very well. It would be better if you had a memory (capacitor) per pixel that will see that the LED keeps the required brightness the full 1/12.5 sec. Then you would have a flickerfree picture. However that implies 1540 capacitors and 1540 transistors and 1540 resistors besides the 1540 LEDs.

Then the current for each LED can be say 10 mA peak white again, but for a white frame still 16A is needed from the PSU.
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Postby johnrpm » Tue Oct 09, 2012 8:10 am

Not sure if it would be fast enough, but an Arduino with 74HC595's and a shiftout library are often used for led cubes, although speed may be an issue.
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Postby gary » Tue Oct 09, 2012 9:34 am

Albert, using ISO_13406-2 (http://en.wikipedia.org/wiki/) as a guide, how many dead pixels will you tolerate before you consider the panel defective? ;-)
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Postby Steve Anderson » Tue Oct 09, 2012 12:46 pm

Klaas Robers wrote:Then the current for each LED can be say 10 mA peak white again, but for a white frame still 16A is needed from the PSU.


Car battery? The sane solution is buying a ready-made switched-mode PSU, but that's additional cost for what is a hobby.

As I mentioned before, my idea is purely conceptual, I have no intention of actually building it. It would be quite complex but not impossible.* It would require a modest amount of number-crunching so while you're about it you may as well blend in Graham Lewis's frame-rate multiplier to reduce/eliminate the flicker.

Because that would be done in software it us unlikely to increase the chip-count.

Steve A.

*I think wiring up 1500+ LEDs each with two pins actually is going to be 90% of the effort...let alone anything else in a similar quantity. But Grant did it!
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Postby gary » Tue Oct 09, 2012 1:34 pm

Steve Anderson wrote:Car battery? The sane solution is buying a ready-made switched-mode PSU, but that's additional cost for what is a hobby.


Oh a salvaged computer PSU should be perfect for that application - the last couple I bought from the recycle shop cost $2 each.
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Postby Steve Anderson » Tue Oct 09, 2012 2:25 pm

gary wrote:Oh a salvaged computer PSU...


True, if you run this thing off 5V which should be possible, but if 12V a PC supply isn't quite up to it. But good suggestion.

It depends on what losses there are in the drivers at these sort of currents and the LEDs will require increased drive volts. The only answer is to try a small-scale version first.

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Postby Viewmaster » Tue Oct 09, 2012 6:23 pm

Klaas Robers wrote:But then you will see the flicker very well. It would be better if you had a memory (capacitor) per pixel that will see that the LED keeps the required brightness the full 1/12.5 sec. Then you would have a flickerfree picture. However that implies 1540 capacitors and 1540 transistors and 1540 resistors besides the 1540 LEDs.
.


Yes Klaas, An analogue storage memory is required to keep the LED's on until the next frame scan. The capacitor is the easiest way, but as you say that is 1540 C's to say nothing of the extra 3000 soldered joints required.
Still after soldering up over 3000 on the LED's and hundreds more on the circuitry what's an extra 3000? :wink: Oh and the cost too.
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Postby Viewmaster » Tue Oct 09, 2012 6:37 pm

Steve Anderson wrote:*I think wiring up 1500+ LEDs each with two pins actually is going to be 90% of the effort...let alone anything else in a similar quantity. But Grant did it!


I've been looking into this and it's not quite as bad as it might be.
5mm LED's fit well onto veroboard. But the flange at the bottom is bigger than 5mm ( 2 vero hole spacing) so each alternate LED is slightly
up/down on its neighbour..........

DUDUDUDUDUDUD
UDUDUDUDUDUDU
DUDUDUDUDUDUD

Each NBTV row has 48 common negative LED connections so these would solder straight along a continual vero copper strip . The other positive LED connection brought out, extended, and the NBTV columns commoned up at 90 degrees to the common strip..........if you see what I mean :wink:
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Postby Harry Dalek » Tue Oct 09, 2012 7:17 pm

As Gary pointed out Baird did a matrix television also bell labs same sort of idea ...
I was thinking today as you do .. :shock:
I see how everyone is thinking the way to do it is horizontal and vertical scanning circuits ,but looking back at how they did it it wasn't done like this ?.
The commutator just switched all those lights in one row one long line so they just snaked zig zag the lights into a raster form how they wired it to the lights i think.
In any case would it be easier to just take a look at the past and do a modern version what worked from them ?

I don't mean make a rotating commutator but scan only in one direction and just zig zag the wiring to the leds so it would form a raster ?
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Postby gary » Tue Oct 09, 2012 7:30 pm

Steve Anderson wrote:True, if you run this thing off 5V which should be possible, but if 12V a PC supply isn't quite up to it. But good suggestion.

Steve A.


Oh no Steve it depends on the PSU I have in front of me a mere 250W PSU and it's 12V is 14 amps - they get much bigger than that.

I think we had a "back of an envelope" calculation of 16A - well if limited to 14A I doubt you would see much difference.

I'm a bit of a buff on PC PSUs because I use one for my CNC machine. I actually bought a 20V 4A SWPSU for the job but found the PC PSU a better choice. I would like a few more volts though.

I read somewhere that with a bit of modification you can cascade PCPSUs for higher volts (or amps) but haven't tried them.
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Postby gary » Tue Oct 09, 2012 8:00 pm

harry dalek wrote:bell labs same sort of idea ...


Good point Harry, I sometimes forget the yanks had anything to do with the development of television ;-)

harry dalek wrote:The commutator just switched all those lights in one row one long line so they just snaked zig zag the lights into a raster form how they wired it to the lights.
I don't mean make a rotating commutator but scan only in one direction and just zig zag the wiring to the leds so it would form a raster ?


But they had a commutator segment for each lamp (so in Baird's case 2100 segments).

The equivalent of this with (assuming 8 tap shift registers) would require at least 263 shift register chips if my calcs are correct...
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Postby Viewmaster » Tue Oct 09, 2012 8:53 pm

gary wrote:The equivalent of this with (assuming 8 tap shift registers) would require at least 263 shift register chips if my calcs are correct...


Now you are really frightening me with 263 shift regs and all that pcb track work!

BTW, Grant Dixon must have been in his late 70's, early 80's when he built his matrix.
I shall be 80 next year, so I may still have time to follow in his master's footsteps.
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Postby Harry Dalek » Tue Oct 09, 2012 11:19 pm

Hi Gary

Good point Harry, I sometimes forget the yanks had anything to do with the development of television ;-)


I wonder which one was neater ......looking at the Bell lab one makes me think baird had a nicer design .



But they had a commutator segment for each lamp (so in Baird's case 2100 segments).


Now thats determination its matrix television but still mechanical television not only that it has to be the most complicated mechanical television ?

The equivalent of this with (assuming 8 tap shift registers) would require at least 263 shift register chips if my calcs are correct...
[/quote]

I think Mr Baird would be calling us names and the guys at Bell labs would be ebaying them from china if they could ...for me yes a little to much soldering these days . :wink:

Oh Albert i hope i make to 80 and still doing the hobby i think my eye sight will give out but good luck on the project if anyone can do this one you can .
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Postby gary » Tue Oct 09, 2012 11:28 pm

Viewmaster wrote:....

DUDUDUDUDUDUD
UDUDUDUDUDUDU
DUDUDUDUDUDUD



Albert, I have the greatest confidence in you and I am absolutely SURE you you won't have that many duds... ;-)
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Postby Steve Anderson » Wed Oct 10, 2012 5:15 pm

gary wrote:Oh no Steve it depends on the PSU I have in front of me a mere 250W PSU and it's 12V is 14 amps - they get much bigger than that.


OK, things are different to what I can recall. I would have said +5v @ 20-30A, +12v @ (say) 5A, -12V at a couple of amps and -5V at bugger all. Somewhere I've got a couple I ripped out of dead PCs, but the supplies were OK. (...might come in useful one day syndrome) though I have never used one outside of a PC).

As I remember 286's had 120W or 150W supplies (though you could get more watts if you needed them), these days they're at least 250W, I think the HP's here are 350W.

One thing to remember only the +5V (and the 3.3V one these days) supply is regulated, the others 'follow' to a degree depending on the load. They tend not to have any current limiting. So if your load on the +5V rail is quite light (<10A) you could probably pull quite a bit more out of the +12V rail.

The back-of-a-fag-packet calculation is of course for an all-white field, with real video that 16A would average out around 10A as a very rough guess, maybe less.

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