[Swlug] Further interesting calculations

[Colin Law]

The ESP devices have multiple built in hardware timers. You should be able
to use those to do what you want you want.

Colin

On Thu, 1 Jun 2023, 01:15 Rhys Sage via Swlug, <swlug at mailman.lug.org.uk>
wrote:

> The concept is to make a microflash. Those are designed after a trigger
> signal to wait a user-specified period then to give a brief burst of light
> and to do that only once before reset.
>
> The aim with the flash is to take pictures similar to those in my book:
> "High Speed Photography - it's not Rocket Science". Those were taken with a
> Canon 540EX flash that I sold about a decade ago. High speed photography is
> a case of opening the camera shutter and locking it open then using the
> flash to do the exposure. The photos are taken in absolute darkness bar the
> flash. The shorter the flash, the faster the action that can be frozen. A
> Canon 540EX has an absolute minimum exposure time of 1/38,000th of a
> second. The very fastest Xenon flash has a minimum exposure time of
> 1/100,000th of a second. Xenon cannot go any faster because although it is
> inert, it has an afterglow that takes a while to fade.
>
> An LED flash can give exposures down to the millionths of a second as
> there's zero afterglow. With my 540EX, the best photo I could take of a
> .177 air rifle pellet travelling at 1200fps was quite blurry. The delay
> timer I have worked well and got the exposure time spot on. I want to build
> an all-in one unit.
>
> I have an LED array I built 15 years ago with 227 white LEDs on it. I'm
> trying different resistors to get optimum brightness since the online
> resistor calculators are wrong. I should have put resistors when I built it
> but they're all in parallel so now I need super-duper 15W resistors. I have
> to order those.
>
> The variation in the delays on the Arduino and Pi are a little worrisome
> but I should not be gauging equipment using its own timers so I have
> ordered a timer kit that I'll have to solder together. Looking at the
> pictures, that shouldn't take more than an hour to solder and assemble.
>
> So - the timing events needed.... From audio trigger to flash. This can be
> variable and could be anything from 1/10th of a second down to 1/50,000th.
> Nothing particularly fine needed there. I can always move the audio sensor
> back a bit to give myself more time delay while remembering the speed of
> electricity is 270,000km/s. The flash duration needs to be as small as
> possible variable up to 1/30,000th of a second and I'm hoping to go orders
> of magnitude faster than 1/100,000th.
>
> For my own use, the fastest thing I might be photographing would be 9mm
> NATO which travels at up to 1,400 fps unless I can borrow something that'll
> shoot .220 swift at 4,665fps.
>
> For the flash duration, reading Edgerton's book (and a few others) it
> seems that if I power (in their case an air-gap flash) the flash from a
> capacitor discharge then electrolytic capacitors are too slow and the type
> needs to be air-gap or mylar. I don't want to use an air-gap flash even
> though I have some of the kit to build one (don't ask) as they're a bit
> spicy in use, carrying around 50KV. The other downsides to air gap are
> copious quantities of ozone, intense UV light and radio interference.
>
> Sorry if I sound a bit boring here. I wrote a couple of books about it.
> Both could do with a massive re-write as they were written during one of
> the worst, most traumatic periods of my lfie.
>
> So, having blustered profusely and bored everybody to death, I'll answer
> Colin's question...
> I really need both bits of timing - they delay and the exposure to be
> predictable.
>
> Rhys Sage
>
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