hi, I'm working on a time fountain and could use some help.
A time fountain is basically an optical illusion that makes water drops seem to freeze in mid air.
i could start explain the hole thing but i rather explain what relevant for the question. if your interested theres an explanation in this link.
http://cre.ations.net/creation/the-time-fountain

ok so heres the deal.
we have leds aimed at water drops, assume that if leds are off water drops are invisible. meaning when i turn them on permanently you will see them, if i dont you simply wont.

drop is falling from 0.18m and is detected with accuracy of several uS (microsecond 1/1000000).
I'm working with a microprocessors and programming it I'm assembler - meaning we are talking about accuracy of microseconds.

The effect happens IF -> after each drop is detected we wait X time, then turn leds on for Y time then turning them off.

what happens here is, after the drop is detected i wait some time, until drop falls away from the top a certain distance, then i light the leds on, capturing the location of the drop, when I'm lighting the leds it should be just long enough to see the drop in its current location only!.
if drop rate is fast enough to get close to our eye ability to capture 30 frames per second (try to get as close as possible to: drop every 33 milliseconds),
we will capture a different drop in the same location every time and it will seem as drop is frozen in mid air.

i hope I'm been clear here, I'll start with just this question and see if I'm understood since thing get more and more complcated.

my question is how to calculate X and Y to be optimal for our eyes to see.
it seems to me X can be calculated through X=0.5gt^2.

so this is just to get the topic started ask me anything u don't understand and when wer clear il get more into it.

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This is a lot less complex than it seems. Don't bother calculating anything. Just look at the drops while adjusting the LED flash and/or drip rate.

 

Math is fun, though, TheVictim...

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that things awesome!! i think if i was going to make it, i would do what thevictim said and just look at the drops, while changing the flash rate of the led's

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problem is drop tare isnt constant so constant flashing isnt good.

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Am I misinterpreting this? It seems obvious to me that the best "exposure" time is zero, but then you couldn't see the drop. The shorter the exposure time is, the less blurry the drop will be. However, with shorter exposure time, you need a brighter flash from your LED, since your eye tends to integrate the light. It's the same principle as lens aperture and shutter speed in a camera.
I think I would detect the water drop by placing an IR LED and photodetector immediately above the illumination LED. Then you don't have to time the fall over the entire 0.18m. Maybe you are already doing this?

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Apparently it is possible to get the same effect just by using a 555 timer adjusted manually.
That is how the maker of this one claims to have done it:
http://www.youtube.com/watch?v=IcMfMKK5nWo

 

You need to read the OP's last post.

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i am detecting the drops, but not with IR leds, thou it is possible.
it is also possible to do with a 555 timer as long as the drip rate it constant, and im working hard to get it as constant as possible, yet still there are changes in the drip rate which spoil the effect, thats why im trying to sync the flashing for each single drop.

im trying to better understand the consept, i found that it best to light the lights for 0.01s in order to see the drop as a single drop, my problem is when to light them.

i know exactly when each drop falls so how should i do it? should i wait X time after each drop and flash once or twice or more? or should i take every 2 drops and calculate the time between them then get the drop rate and match to it a flash rate? and exactly how to do that?

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Souper man

Those UV LEDs cant be good for you...

 

why??? they are only led's, i don't think they have enough power to do any harm???

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i just tried making one of these fountains with a strobe light, and it did somewhat work, but the strobe light wouldn't fire reliably enough to get the full effect, i could get it to slow down the drops though, that was really cool

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2. If it's mushy, It's biology.
3. If it doesn't work, It's physics.
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www.laserchat.org IRC chat for laser and electronic related stuff.

 

Souper man

Well, if you have high MCD rating UV leds and you left it on for like a hour and you sat there staring at it, then I suppose you could get some skin damage...

 

I doubt it, most aren't even real UV but deep violet (390nm to 410nm) which does cause some fluorescence and can damage your eyes (only if you stare into the beam for long enough) but won't cause tanning or skin cancer.

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Souper man

Hero, I have stared into my UV LED for like 1 min...
It is UV, because it would glow up some of my floride rock samples.

oops...