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871  Forum 2005-2010 (read only) / Interfacing / Re: Project: Stabilisation of a laserlight on: October 08, 2010, 11:37:31 am
You know, as I read this, one possible solution for his need for an ultra-fast pan/tilt mirror would be to use "galvanometers", but not hacked speakers- I would think the best solution would be pivoting the mirror with a selenoid vs. a spring in each axis.

Selenoids and springs are available for cheap money, and not too much is going to be faster without huge expense...  PWM driving the selenoids would give you very precise control...

Since the device's purpose is aiming, calibration isn't needed- even if the resilience of the springs or the pull of the selenoid (brownout?) changes, you're correcting it on the other end.  You could easily wind the selenoid coils yourself, and even use rubber bands (or even a couterweight, if you want to be downright medeival) instead of springs.  The whole idea is that the selenoids are constantly pulling against an opposing force- pick your own poison.

I would think a design like this would be a LOT faster than any servo.. and potentially more accurate if you tweaked it right...

Last but not least, I'd been wondering how hard it would be to play around with one of those DLP chips they used for rear-projection TV's for a while there... all they are is aimable mirror arrays..
872  Forum 2005-2010 (read only) / Interfacing / Re: $39.99 robotic arm? on: September 29, 2010, 03:30:21 pm
Interesting..I may read up on it a bit then.  Was just cruising for some parts on ebay when I came across it.  Surprised, expected a reply saying it is complete crap..

I've been fiddling with the idea of using a robotic arm or xy table (ala cnc) to paint (using oils or acrylics) with an actual brush.. decoding JPEG into say, 32 colors, and premixing (or even automixing!) the paints.. to function a lot like a plotter, but a lot lower resolution.  May be just a pipe dream, but pretty sure it would be possible and fun to try.

I've been known to say "Now here's where Wile E. Coyote went wrong- I bet I can make it work..." or "Hold on tight, I saw this in a cartoon once...."
873  Forum 2005-2010 (read only) / Interfacing / $39.99 robotic arm? on: September 29, 2010, 02:15:18 pm
okay... any thoughts on this?  I'm sure it's not that accurate and all that- but maybe with some encoders..
874  Forum 2005-2010 (read only) / Interfacing / Re: Wireless Magnetic Induction LED on: September 25, 2010, 11:58:09 pm
Rich- actually, I think that's a beam/sensor photo arrangement.  Seems to be the "standard" for the current generation of these things.  I was thinking of using one at the bottom of the object suspension, but the idea is the same and much easier to pull off from above.  

We really ought to move this discussion to another thread however.. I'm posting this as a bump, because he still needs some help.  I know enough to be dangerous, but there are plenty of folks here that can help him.

In summary (as far as I can see) he wants to drive a primary coil controlled by an Arduino pin, with a secondary as an air core transformer, to drive an LED.  My best shot at this would be a Triac, winding a primary, and simply finding a decent secondary winding by experimentation, as there's so many variables.

However, there's probably a better way- so jump in, guys!

(sorry for Hijacking the thread there!)
875  Forum 2005-2010 (read only) / Interfacing / Re: Wireless Magnetic Induction LED on: September 25, 2010, 08:35:22 am
Well, I couldn't find the one I was looking for.. but I had seen a version controlled by an op amp circuit with a triac and CDS sensor which was suspending a 20 oz claw hammer at about a foot.. and it was being run off the mains on a wall socket- so it couldn't be pulling more than 15-20A @ 120v or it would trip the breakers.  Judging by that alone, which is orders of magnitude larger field required - it may be a power pig and not very practical.. but possible, indeed.  Mine (and the author of the thread's) goals are a LOT less ambitious..  if his coil, led and such weighed in at an ounce, I would be suprised.  In fact, I don't see him wanting the maglev at all, only current transfer.. I'm the dope who threw maglev into the mix... hehehe

Since he only wants to power an LED inductively, a couple of volts at a few mA, he might be able to get away with PWM and a power transistor for his setup, right?  If it were me (bad ideas abound), I'd make the primary and just fudge out the secondary as needed.  Yeah, I know there's math.  You don't need math until you've blown off ALL of your fingers.  Until then, it's a matter of doing everything in base "x", where x is the number of remaining digits, pun intended.

876  Forum 2005-2010 (read only) / Interfacing / Re: Wireless Magnetic Induction LED on: September 25, 2010, 08:12:58 am
Actually, Mike.. it's been done before, in many different ways.  Here's a youtube clip of someone who has basically made a smaller-scale version... though not that much "smaller" in scale than my thoughts:

In fact, the kid is using an Arduino and PWM to control it.. looks like someone beat me to it quite nicely.  Still, won't necessarily stop me from making mine.. and maybe some improvements..

The most basic form operates by just finding the "sweet spot" of an electromagnet running on pulsed DC... pulse the DC at the right freq, and the magnet pulls up and drops the ferrous "load", suspending it against gravity as the coil is cycled on and off.  In his (and the design I was thinking of), the field is either modulated or switched rapidly enough that the rise and fall of the field is somewhat smoothed out- you don't SEE the rise and fall-but it's there.  In fact, I think I remember an original design (may have even been a Tesla design) where the pulses are made by a mechanical vibrator- a relay that acts as a flip-flop- and that design was OLD.. So, to answer your question, I haven't done the specific calcs for my plan yet, but they are well within reasonable limits, and have been done by amatuers and students many many times.. not to mention I suspect there's more than a few designs of magnetic bearings in use industrially that are similar.

I wonder if we could use a few hall effect transistors, a pulsed electromagnet, and some signal conditioning to build a poor-man's MRI...
877  Forum 2005-2010 (read only) / Interfacing / Re: Wireless Magnetic Induction LED on: September 25, 2010, 06:12:47 am
Interesting.  I've been thinking about much the same thing recently.  In my mind, the best approach will be a ferrous core in the primary, and having a primary that is heavily powered as well as a fair number of turns, to maximize the field strength.  My field should be powerful enough to suspend around a half pound at a distance of several inches, for my project to work.  That's a powerful magnetic field, a secondary powerful enough to light an LED SHOULD be possible.

I have been thinking about building a maglev rig (electromagnet vs gravity, arduino controlling magnet, on/off sensed with phototransistor in suspension location) and was thinking about much the same thing- could the suspension field be harnessed and rectified and used to drive an LED (or skip rectifier and let LED do it itself-- it is a light emitting DIODE).  

Since the electromagnet (which will work better than a total air-core because of the ferrous center) sets up field of pretty decent power, it should be a pretty decent primary. (this assumes design to use AC to drive magnet- I'm thinking Triac- and though original mental design was on/off, PWM could work too..hmm...).  

If I assemble the magnet and power it up, I should be able to make and test various secondary coils with a meter, and simply find the right coil by shooting in the dark and tweaking, at least that is the plan... and end up with a Maglev wirelessly powered LED..
878  Forum 2005-2010 (read only) / Interfacing / Re: Superbright LEDs and Aruduino Duemilanove on: September 24, 2010, 08:16:29 am
I'm not the right one to do it- when dealing with components and tolerances, I'm notorious for the "blue smoke diagnostic" method.. but the site could REALLY use a definitive no-brainer circuit library, the ones that are needed over and over.  LED driver via transistor (with both sink and source configuration and WHY), a good explanation of what a Pullup resistor is and why we're happy they are built in, a basic op-amp setup for microphone input, and the basic use of optoisolators and voltage dividers.  In reading the forums, these same needs arise over and over, re-inventing the wheel is a grand hobby, though not very productive.

However, you will then be inviting people like me to re-invent the wheel in a more asthetically pleasing and easy to carry rectangular shape..

I'd love to see referenced the most common components- 555's, 741's, 2n2222, etc... so that the most likely component that will be found (at the local radio shack or whatever) and the support circuitry then lines up (if we know gain, for example, we can "standardize" the resistor values).  If we assume that 2n2222 or direct equivalent will be used for all NPN switching circuits, we'll be right 90% of the time and include the formulas for other transistors to produce the proper values.

I like many others have *some* electronics background, but fall short in a lot of areas.. many times just fiddling till it works instead of planning and properly designing.  A "cheat sheet" of common circuits using the most common components would be a great thing to have.. I for example know driving the LED with a transistor is the right answer, but I would have done it as a current sourced from the pin- a much less robust design, even if it did work.  There's plenty of really good engineers here who know better than to do things the (wrong) way I do things...  

Other than that, I recommend as a GREAT reference to electronics in general...
879  Forum 2005-2010 (read only) / Interfacing / Re: Atari SIO Interface using Arduino as SIO2USB on: August 16, 2010, 12:20:08 am
I'm an old Atari guy.  Pure awesome.  Bravo.
880  Forum 2005-2010 (read only) / Interfacing / Re: Arduino analog input on: August 15, 2010, 12:53:24 pm
(rasies hand sheepishly)  NPN switching transistors are cheap and make a neat popping sound.  Why do math when it's easier to just jam another one in after you pick the silicon bits out of your corneas?

I should post the "design" (lampcord and wall switch) for the cannon driven by electrolytic cap explosion I built years ago.  

ANYWAY, this is not really that far off from the automatic gain control thingie I'm working on, basically driving the gain by using a PWM output and a capacitor.  I'll crosspost if I get a good solution.  I'd say the chances are roughly as follows:

50% good solution, 25% electrocution, 20% "incediary mishap", 5% creation of a naked singularity.  All in all, those are odds I can live with, and so can most others outside of a certain radius.
881  Forum 2005-2010 (read only) / Exhibition / Re: Camera strobe modification on: January 23, 2011, 05:53:55 pm
Well, been browsing over at the CREE site as well as several other makers.. CREE just released a document regarding pulse-driven power LED's at multiples of their rated values.. basically a document from their R&D department showing some basic overdriving info.  Interesting, and they take great pains in noting that overdriving will void warranty and probably shorten life of the emitter.  That being said, the document gives reference to pulse-running short durations at up to four times the rated current, giving up to three times the rated light output.  Heat is the monster, and the possible melting of the wires that go to the die.  Pulsed very quickly, like in the microsecond range, electromigration may be a bigger problem than heat.  The article also refers to overvoltages into the tens of volts, but overcurrent is probably a better option.  Maybe I'll just hook up two or three "D" alkalines with no current limiting, those pups can throw a couple of amps for short periods.  I have a 1w Luxeon that is begging for abuse..  I mean, let's say I can get 3x the rated output, but it will shorten the LED life to say, 10k pulses at that output.  Considering a new power led is only a buck or two, even a few hundred "flashes" would be plenty cost-effective to burn an LED out with, considering..

As for intensity, remember light decreases as the inverse square of the distance, or something to that effect.  I can get an LED awfully close, within inches, just out of frame... huge power isn't actually huge at all, if it's further away...

As i understand, there's potentially tens of amperes at hundreds of volts blowing through that xenon tube- can a transistor of reasonable price handle somthing like the spike that it would need to interrupt?

I'd love to have access to some of that kind of high-end studio equipment.. but I needed to save months to even get the Interfit el-cheapo setup.  $299 for two 150 w/s strobes with 100w halogen modeling lights, stands, soft box, bounce umbrella, and cables.  One of the cheapest setups on the market, but rated high for semi-pro usage.  If you are in the market for the cheapest possible (but stil usable) light rig, I recommend it heartily.  Slow to cycle, but the setup provides more than enough for decent head shots and small areas.  heads are adjustable from full to 1/8 power.  I use them with strobes for standard portrait shots, and with one additional modeling lamp (like the CREE) without the strobes for impact shots like the one above by using a good old Nifty Fifty.... f1.8 50mm, slow and noisy but try and beat the image without spending a grand on "L" glass.  At a hundred bucks new, if you don't have the "L" toys, you really MUST have a Nifty, IMO.   With that short DOF, you can really get tight on subject focus with a really nice softening.  Huge aperture = luv

The heads you are talking about start in the range of twice the price of my whole light kit- for a single head with no accessories...  modifying a $3 disposable camera flash seems a better idea than selling my soul (and still maybe needing to modify) for a pro monolight.....  As it stands, my next purchase needs to be a new body, my poor little 350D (Rebel XT) has seen a lot of milage, and Canon won't even fix them anymore under standard rates.  Dreaming of a pro body, but even one of the newer XT-series "Pro-sumer" models would be a big leap in gear for me.  The gig that shot above was taken for was defunded.. and that job was supposed to sock away most of the cash for the new body.. so I'll be milking life out of that 350D for a while yet.

882  Forum 2005-2010 (read only) / Exhibition / Re: Camera strobe modification on: January 23, 2011, 01:44:11 pm
Well, I now have a reason to rip apart something I've been using for less nefarious purposes... Home depot sells a 10w CREE LED light- warm white, 2700K, CRI in the high 80's.  I got one and have been using it as a great little portable modeling light.  Coupled with a pair of Interfit 150's and some creative reflector work, it makes for a cheap (under $350) and very usable portable portrait "studio" setup.  I recently posted some shots taken with the CREE LED light.

However, there is a significant delay between applying power and the led actually striking.. enough that it's noticable.  I'm sure that's a function of the driver circuit.

I *should* be able to place some type of control circuit in the works, and be able to use it... yet another hack to try smiley-wink

Here's a shot from that series.  No strobes were used for this shot, it was "Rembrandt" lit 45 degrees off subject on both sides with 75w of halogen at about three feet through silk softboxes for fill.. but the main direct lighting is that 10w CREE.  It's quite visible in the shadow tones and uplighting.. the halogens are at her eye level.  If anything, it's a bit too deep in rendering of the reds...  I am not displeased with the rendering, it works really well if used in concert with more standard light sources.

883  Forum 2005-2010 (read only) / Exhibition / Re: Camera strobe modification on: January 23, 2011, 01:27:53 pm
Well, I've been looking at Sam Wasserman's strobe pages and links frome there, one of which details the modification of a kodak max disposable camera flash, by replacement of the storage cap- from 160uf to a 5uf (chosen because the author had it in junk box), resulting in a power reduction (duration reduction) to 1/36th the original.  He goes on to make a repeating strobe, but for the purposes I need, simply the reduction in flash duration is all that is needed.  For most photography, you'd like a longer flash duration.  For this, the power isn't as important as the speed.

Excellent discussion of abuse of strobes in general:

Assuming we are talking typical cheapo, that's a 1ms strobe.. which already is faster (lower power) than the studio flash.  If the result is real- 36 times faster - that's a VERY usable interval.

For stop-motion, you don't need a ton of light- but you need that light to come on and off VERY fast.

What you've suggested is called a quenching circuit, and it's what is used in high-end strobes costing thousands... the damping circuit to interrupt the arc takes HUGE energy dissapation, methinks..
884  Forum 2005-2010 (read only) / Exhibition / Camera strobe modification on: January 23, 2011, 11:29:31 am
Recently, I've been using the Arduino to do some high-speed camera strobe triggering to accomplish stop-motion photography.  Standard project done a thousand times- electret microphone, sound triggered.  Typically, when using an Airsoft gun to shoot Christmas Tree bulbs, I use a 75ms delay from sense of the sound to firing of the strobe.  The shutter is otherwise open.

The problem I'm running into is that the flash duration from my Interfit 150 studio head is way too long, even dialed back to minimum power.  I'm getting flash durations of around 1/2000sec, where I'd like to be dealing with flash durations more in the range of 1/10,000 or less, to freeze as much motion as possible.  As the flash duration IS the exposure time, 1/2000 sec is pretty slow when dealing with exploding glass.

So, I've done research and have thought of several solutions (short of glacialwanderer's spark-gap flash).

One is modification of a cheapo flash (like from a cheapo disposable camera).  Inherently the overall power is lower of course, but it's typically a shorter duration flash to get that.  As the trigger on these is high voltage, I'll probably use a 5v relay (they have 20msec switch time, which I can take off the strobe delay).  I don't think I've got a transistor or SCR handy in that HV range, but a PCB-mount mini-relay should suffice.

In reading, one method is to replace the flash storage capacitor with a smaller one, resulting in lower energy, which is shorter flash.  I may try this if i have a cap that's in the right range.  If I don't, I was thinking about being a real idiot:

In the flash, an oscillator is fed through a transformer to charge a HV cap.  Instead of reducing the cap, couldn't I instead place a bleeder resistor across the cap, and feed the transformer PWM?  In this way I could control the charge level of the storage capacitor by PWM.  Sounds good on paper until I start working the WATTAGE of that bleeder, I'd need a very high wattage (high voltage at high current storage) resistor, wouldn't I?


Last but not least, also looking at trying to use a couple of power led's I've got around.. led's react in the nanosecond range...  I know the actual power is low compared to xenon- orders of magnitude, in fact- but proximity to the subject (inches) may compensate for that- nothing to lose in trying....
885  Forum 2005-2010 (read only) / Exhibition / Re: Power LED's for Photography on: December 07, 2010, 08:44:24 pm
These are quite warm, if I remember right, 2700K.  Yep, CRI of 92... not too shabby.  575 Lumens and they are dimmable by standard dimmers (interested in how they manage that.. pwm maybe?).  The lack of a filament or glass to break, the long life, and the lack of heat are all big wins.  With minor modifications they should be able to converted to run from DC, and with that low current draw, battery power is within reason.  Here in one of the color shots, you can see just how warm the lighting is.. it's a bit exaggerated in terms of reds as I had the camera set for flash spectrum:

Here in Massachusetts the price is subsidized by Nstar, so instead of $49 each they are $19.99.  

Wouldn't you know it, too- just got a call from the client, the project has been canceled due to budget constraints.  All that work is great for the portfolio, but there went what was supposed to be xmas shopping cash.  Paying gigs are few and far between for me, this truly sucks.  When all's said and done, I walk away from the gig with less than a hundred bucks profit for three days work.  Suffice to say I'm pissed.  Not a chance they are getting anything past the low-res proofs they've gotten.. not to mention I will still have to drive out there and tear down and transport back my gear, which was left onsite for the next shoot.  Hauling heavy lighting gear is almost a sure-fire way to kick me into an attack.. not pretty.  That, and I need to call Heather and tell her we're out of a job..

Spewing some creative expletives and mixing a drink.
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