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Simple High-Speed photography

A place to ask general spud cannon related questions.
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Unread postAuthor: jimmy101 » Wed Dec 31, 2008 4:20 pm

Insomniac wrote:Also, what happens when you connect a bunch of caps in series if they don't all have the same uF rating?

1/C<sub>total</sub> = 1/C<sub>1</sub> + 1/C<sub>2</sub> + 1/C<sub>3</sub> + ....

Cap's in series are just like resistors in parallel. Doesn't matter if they have the same value or not, just plug'm into the formula to calculate the effective (C<sub>total</sub>) capacitance.

The resistance of the caps will just add as you wire them in series. I believe that'll pretty effectively undo whatever speed gains you get from dropping the capacitance by wiring'm in series.

Some stuff on flash units at that you might want to peruse;
http://www.chem.helsinki.fi/~toomas/pho ... ml#working
http://www.repairfaq.org/REPAIR/F_audio ... DIOFAQ_001

Just thought of an easy way that might work to shorten your flash duration (at the expense of flash brightness). Don't charge the cap all the way up. Turn the flash board on while monitoring the cap's voltage. When it hits 250V (or 200V or 150V or ...) remove the battery. The lower voltage in the cap means it'll drop below the hold voltage for the xenon tube faster, shortening the flash duration. If you cut the caps charge voltage in half then you'll only get 1/4 the power into the flash tube, not sure exactly how much that will shorten the flash's duration.

You might not be able to continously monitor the cap's voltage as it is charging. The charge circuit supplies very low current and the load of even a DVM may be too much for it. So, charge for a few seconds, remove battery, briefly touch the meters probes to the cap to get a voltage reading, repeat as necisary.

If you drop the cap's voltage too much there might not be enough energy in the trigger cap to light it off. Might have to use the trigger from a second board that is charged all the way up to 300V.

So far it looks like you are doing pretty well. The images look great.
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Unread postAuthor: Insomniac » Wed Dec 31, 2008 10:07 pm

Image

Another pic I took, by firing it through a cd case (was hoping for more shrapnel) and the flash was triggered by the projectile hitting some foil.

I've decided that I won't worry about the flash speed at the moment, and insead find a way to trigger it based on sound. Some circuits, such as the Make homemade strobe photography circuit seem a bit complex and expensive. Further googling found me THIS.

If the comments are to be believed it will cost about $10 to make (probably a bit more but hopefully not by too much) It doesn't have delay controls, although this isn't too important to me.

What I need to know (hopefully you understand electronics well enough to figure this out) is just how many volts it can take across the flash trigger. Will it be fine directly connected to the 60+ V the disposable's trigger uses, or will I need to use an SCR to make a low voltage trigger, and the connect that to it instead?

If I make this I won't bother with the light sensing part of the circuit, some people in the comments reported having trouble with it and I want this a cheap and as simple as possible.

Once I get this trigger set up I'll work on speeding up the flash.
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Unread postAuthor: D_Hall » Thu Jan 01, 2009 12:36 pm

Insomniac wrote:Hmm... I think your sandwich might work better with alfoil-paper-alfoil... My reasoning is that paper tears rather than streaches, so I think it's more likely the foil would touch the other side. I will give it a shot later and see what happens.

You may be right. As I said, there are many different kinds of make paper (and companies that sell it, believe it or not). I mentioned the type I had personal experience with but my situation was greatly different than your's. What was ideal for me may not be ideal for you.
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Unread postAuthor: Insomniac » Thu Jan 01, 2009 5:18 pm

I tried the paper-alfoil-paper combination the other day and it worked perfectly. Although the large amount of shiny foil and no delay timer makes it a bit tricky to photograph well.
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Unread postAuthor: jimmy101 » Thu Jan 01, 2009 8:28 pm

Insomniac wrote:I've decided that I won't worry about the flash speed at the moment, and insead find a way to trigger it based on sound. Some circuits, such as the Make homemade strobe photography circuit seem a bit complex and expensive. Further googling found me THIS.

If the comments are to be believed it will cost about $10 to make (probably a bit more but hopefully not by too much) It doesn't have delay controls, although this isn't too important to me.

What I need to know (hopefully you understand electronics well enough to figure this out) is just how many volts it can take across the flash trigger. Will it be fine directly connected to the 60+ V the disposable's trigger uses, or will I need to use an SCR to make a low voltage trigger, and the connect that to it instead?


The output triac in the linked circuit is rated to 400V. I think it'll be able to handle the 300V (not 60V) that is present across the photoflash trigger contacts. The triac is part of an optocoupler, a MOC2030, the spec sheet is at http://www.ieeta.pt/~alex/docs/DataSheets/MOC3020.pdf.

The linked circuit still seems a overly complex. The TRIAC should be triggerable with just a generic photodetector gate setup. Basically, an LED shining onto a phototransitor. The LED needs a battery and resistor. The phototransistor needs the battery and perhaps another resistor. The TRIAC (or SCR), triggered by the phototransistor, controls the flash unit. The flash will fire the instant the light beam from the LED to the phototransistor is broken. Perhaps something like the completely untested circuit.
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Unread postAuthor: FishBoy » Thu Jan 01, 2009 8:38 pm

I wish i had replied to this earlier, but one of my other hobbies is photography and I will definitely be trying this in the next week. I have one question though; where on the camera circuit is the flash switch/trigger?
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Unread postAuthor: jimmy101 » Thu Jan 01, 2009 9:20 pm

FishBoy wrote:... where on the camera circuit is the flash switch/trigger?

In the shematics it is generaly shown as a pushbutton switch. Usually between the trigger cap and the HV trigger transformer.

On an actual flash board you need to figure it out as you take the camera apart. Look for wires, or thin pieces of copper sheet, that go from the flash board to the either the shutter release button or the shutter itself.
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Unread postAuthor: FishBoy » Thu Jan 01, 2009 10:03 pm

jimmy101 wrote:
FishBoy wrote:... where on the camera circuit is the flash switch/trigger?

In the shematics it is generaly shown as a pushbutton switch. Usually between the trigger cap and the HV trigger transformer.

On an actual flash board you need to figure it out as you take the camera apart. Look for wires, or thin pieces of copper sheet, that go from the flash board to the either the shutter release button or the shutter itself.


thanks a lot, I'll look for that. In the somewhat likely event I can't find it, would someone be kind enough to post a pic of a circuit with an arrow MS painted in pointing to the trigger? (btw, sorry for semi-hijacking this topic)
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Unread postAuthor: Insomniac » Fri Jan 02, 2009 1:34 am

FishBoy wrote:
jimmy101 wrote:
FishBoy wrote:... where on the camera circuit is the flash switch/trigger?

In the shematics it is generaly shown as a pushbutton switch. Usually between the trigger cap and the HV trigger transformer.

On an actual flash board you need to figure it out as you take the camera apart. Look for wires, or thin pieces of copper sheet, that go from the flash board to the either the shutter release button or the shutter itself.


thanks a lot, I'll look for that. In the somewhat likely event I can't find it, would someone be kind enough to post a pic of a circuit with an arrow MS painted in pointing to the trigger? (btw, sorry for semi-hijacking this topic)


Hah, don't worry about it. On pretty much every disposable camera I've dismantled, the trigger is two very thin, narrow bits of copper that stick out at the side.
Image

In this example it is the two bits of metal right next to the capacitor. Touch them together and POW, the flash fires.



On a completely unrelated note, I got bored today so I bought some transistors and resistors (only needed one of each, but I bought more in case I screwed up), bought an old second-hand completely busted computer for $3, ripped the ferrite toroid out of the PSU, and made a Joule Thief. Pretty basic, but there is somthing satisfying about seeing an LED light off a single AA battery using a transformer that you hand wound. (It's actually the most complicated circuit I've ever constructed, I've never worked with transistors before :lol: )

I'm going on holiday for a week tomorrow, so I won't be able to respond for a while. Be sure to post the images you come out with though, I'd love to see them.
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Unread postAuthor: CpTn_lAw » Fri Jan 02, 2009 6:01 am

For the "touching the capacitor leads" thing...well, don't do it ;) It doesn't "tingle" it really hurts; Well, touching it with two fingers from the same hand must burn a little and tingle, but touching it like i did with one finger from each hand...isn't funny at all, and i wouldn't do it again even for a large amount of money (or fully prepared women ^^)
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Unread postAuthor: Insomniac » Fri Jan 02, 2009 6:37 am

Yeah, I never want to touch a fully charged photoflash cap. I've touched the trigger leads before (which shocks but it isn't too bad) and I've shocked my foot with the trigger cap itself (depending on where I touched it, I either felt nothing or a tingle down into my toes) and I've also shocked myself with the bare circuit, minus the capacitor (is pretty unpleasent, makes a constant, painful sting where the electrodes touch your skin)

Isn't electricity fun?
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Unread postAuthor: jimmy101 » Fri Jan 02, 2009 2:20 pm

Insomniac wrote:Isn't electricity fun?

Isn't 300+V and 5J from a free circuit that even came with it's own battery fun! :P
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Unread postAuthor: FishBoy » Fri Jan 02, 2009 3:33 pm

Ok, I just set up my own system and I got a few pictures, but when I try to upload them it says "tried to upload empty file." What does this mean??
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Unread postAuthor: frankrede » Fri Jan 02, 2009 4:01 pm

Insomniac wrote:Yeah, I never want to touch a fully charged photoflash cap. I've touched the trigger leads before (which shocks but it isn't too bad) and I've shocked my foot with the trigger cap itself (depending on where I touched it, I either felt nothing or a tingle down into my toes) and I've also shocked myself with the bare circuit, minus the capacitor (is pretty unpleasent, makes a constant, painful sting where the electrodes touch your skin)

Isn't electricity fun?
You should purposely touch it, its quite the experience;)
Now really, you should, its not like a stungun, its like being punched in the chest.
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Unread postAuthor: rp181 » Fri Jan 02, 2009 4:12 pm

more like cutting your finger off. I had a photoflash capacitor charged only to 180v, and i got shocked. It made me throw the circuit across the room, where it still had enough energy to make the flash go off =p
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