can a LED be as good as zenon for a strobe ? I need it bright enough to see well enough to balance a shaft at 5krpm or so.
LED is so much simpler, I have one hooked up to the motor controller pic with just a 2n7002, it works enough to see the motor phase change, but it was just the white led from a cigar sized laser pointer/led torch. but cant realy see much if have the lights on.
maybe a laser is the way to go ?
how much power will a 5mw laser from such a device cope with in 50us bursts ? Im not too woried if it fails after a day or two of continuos use. Ive got some blown ones anyway maybe I should try one of those.
I think I read somewhere that white LED's are being used as camera flashes.. Maybe find that LED type..
Assuming there's no laser specs available.... I say get that 5mW laser nice and toasty. Sometimes destructive testing can yield faster results.. On average isn't the destructive junction temp of most semiconductors somewhere around 100C? With that in mind, monitor the laser temperature to get an estimate of the junction temp. I have a laser level that uses a lens to project a line. Some sort of beam splitter I guess.. There is no rotating mirror. Trivia: What's that lens called? D from BC
do you mean a fresnel lense? only one I can think of with a fancy name.
the problem here is that diode lasers have an incredibly high power density at the optical surface and this can burn a hole in itself. with most lasers ive used theres a fine line between lasing and destruction, many have crossed this line ! for pulse mode I gues its the thermal mass of the surface. but I dont know what this is, the specs on pointer type lasers is ... wel it isnt.
Unfortunately, it is not possible to achieve the photon flux of a flashlamp with regular solid state sources. And you will notice the fact with the LED flashes replaced by xenon flashlamps in high end cell phones.
Well, typically (as an example), a xenon flashlamp in a stroboscope would utilize about 200mJ of electrical energy to generate photons for
10s of microseconds. That is equal to 10s of kilowatts for a rectangular current pulse. That means, in order to have similar qualities (illumination, time window/ precision) you have to get kilowatt range of optical power from an LED for 10s of microseconds. To my knowledge, it is not possible to achieve corresponding luminosity for brief flashes using LEDs yet. With semiconductor lasers, it is the same problem. Even with very high power QCW laser arrays from Thales for example, you can get max 100W peak (140A maximum with a diode drop of
Thanks for the input, I hadnt given it too much thought other than id need on average maybe a few watts of power at typical efficiencies, ie equal to a small torch, and at 166hz a 50us pulse is short enough to freeze motion quite well, wich is about 1%, so the peak power is about 100 times the average. certainly the leds I used were not particularly bright at all I just hit them with 5v via 1ohm rdson of the mosfet wich is probably quite serious abuse.
The 1W devices are presumably a lot brighter, but theyr not cheap enought to use a whole bunch of them, especialy if theyr being abused like this.
I gues you cant beat a xenon tube, I wonder if you could focus all that energy down to a point, that would be interesting.
- Nope. Could be a cylinder lens (cheap) or a special laser line lens, which has a better light distribution (which might not matter in your application) but is relatively expensive.
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There are also holograms which achieve much the same effect. Think of the "pattern generators" available with super-cheap lasers.
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Many's the time I've wished for a simple square grid, or ring-and-dot pattern, but that would be too useful, too easy.
As to the strobe business, I've seen a lot of LED strobe circuits, so it could work. Again, it depends on your conditions.
Yes ive seen a few led circuits, mine is desperatly simple as the PIC motor controler just drives a mosfet at a certain phase angle, I didnt even bother with a current limiting resistor just let the mosfet and diode battle it out with the full 5v, as it was only on for 50us at 166hz, there is about .6v vds drop accross the 2n7002 driven with 3.6vgs. makes it a bit uncertain as to exactly what the current is, but in the region of an amp, with 2 leds in parallel, the third one doesnt seem to work, but i had it in backwards to start with, probably the reverse 5v killed it.
I was realy hoping someone who had use an led one could say if you can easily see the shaft stopped in motion with say a bunch of cheap leds even in good light or wether even with expensive ones its stil to dim unless u turn all the lights out.
So I cant make my mind up wether to order some leds or a xenon tube, and make a hv inverter and trigger xfmr etc.
I gues I should at least get a bunch of brighter leds and try it. any recomendations for bright leds with realy good performance/cost ? prefereably white ofc.
If you want to know about laser filters you could ask on alt.lasers they know all sorts of stuff like that there, in fact one or two people visit here from time to time, I hang out there for a while while I was trying to strangle a diode laser with 2ghz for my heterodyne distance measurer, also had an interesting discusion about
well a strobe is pulsed by nature, 1% duty cycle seems to be ok to see the motion stopped without to much blur, so a 20ma avg would relate to 2amp pulsed, but I would imagine the efficieny falls off long before 2amps with a
It doesn't work that way. The eye averages light intensity and LEDs efficiency falls off at high power (note that the voltage goes up) so pulsing them at higher rate than the critical fusion frequency is a net loss.
The eye retains the peak intensity. It doesn't average. HP has a good ap note on this, though it's quite old. I couldn't find it on line. Though the effect is well known, Maurice Kanbar (Skyy Vodka inventor) managed to get a patent (5850126) on it.
I am afraid you are mistaken. The eye does not "retain the peak intensity" and is a very effective integrator above the flicker fusion frequency theshold. The integrating ability of the eye has been known and understood for now closing on 100 years although the myth of its responding to the peaks still holds firm with those who have no knowledge of the subject. Search as you may you will find no HP, Agilent or Avago app note that is contrary. Believe me even old B/W televisions work!
At frequencies very very close to the neural response update rate, in the order of 7 to 12 Hz - below the flicker fusion threshold - there is a increase in the perception of the effective intensity. However this is very specific to the individual for any significant effect, your optimum frequency may be 8Hz - mine may be 10Hz, and we will not agree between us on any perceived amplitude increase at a given frequency. The effect itself is also amplitude dependant and varies with visual content and, complexly, the audio environment amongst other possible human sensory stimulations.
Again, the peak retention is well known. Here is some info from a Maxim appnote:
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---------------- An advantage of pulse drive is that the human eye behaves as a partially integrating and partially peak-reading photometer. As a result, the eye perceives rapidly pulsed light somewhere between the peak and the average brightness. This means that a low-duty-cycle, high-intensity pulse of light looks brighter than a DC signal equal to the average of the pulsed signal. An advantage of multiplexed operation, therefore, is an improvement in display intensity for a given average power consumption.
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More examples? Here is a design idea from EDN with the same information:
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----------------- Pulsed LEDs can be brighter than direct-drive LEDs for two reasons. First, the human eye functions as both a peak detector and an integrator. Therefore, the eye perceives a pulsed LED's brightness somewhere between the peak and the average brightness.
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Still more:
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Hey, if this is religion for you, believe whatever you want. Just don't expect me to join your church.
Yes it is, as I stated before, a widely held myth amongst those with no knowledge of the subject. Just because you can offer some references where unsubstantiated statements are made does not deny 75years of science and understanding. It appears that many, as yourself, are more persuaded by the fact that if an unsubstantiated statement is repeated it must be true. It then becomes repeated to further reinforce its voracity.
Why not have a quick web search for temporal vision effects and check on the 'laws' of Broca Sulzer, Bruke-Bartley, and Talbot et al. This is well substatiated science not the silly mumbo jumbo invented by Maxim and home hobbyist groups.
But then why bother when you already know that the CIE is wrong, the earth is flat, little green men.....
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