sorry I took so long to respond, I haven't checked this in a while. I could have used four LEDs, but the minimum voltage to keep up output is 3V, so if I run four, it would only work as long as its above 12V. A deep cycle battery will drop the voltage a bit when a load like that is applied, and though ohms law will drop the current going to them based on the resistors, the effect would be way more significant if each gets <3V.
As for a driver circuit, I could have, but I was pressed for time initally, as I had intended to bring it to a gadget competition at a camp I was attending. Unfortunatealy, the LEDs didn't ship in time, and I didn't see much of a need to redesign. Another light I made just a few days ago using two LEDs does use a driver circuit. As for calculating the resistors, each LED has a frop of 3V, and thus for each LED, just subtract 3V from 12V, then use ohms law for 3A. I ran three, thus a drop of 9V, leaving 3V. I needed 3A, thus 1ohm. two would leave 6V, thus needing 2ohms, and one would leave 9V, needing 3ohms four would leave 0V, thus 0ohms, but leaving the problems mentioned before.
As for the safety issue mentioned, most of that was precautionary. From more than a few inches it won't burn. Becasue it has a ~120 degree spread, the power will very rapidly dissipate, so it's NOT like a laser, but is powerful enough to distract or irritate someone from afar. Basically, I just meant don't shine it at cars or in peoples eyes. It, and almost all things should just be treated as though they are more dangerous than they really are.
And finially, does anyone have any advice on easy to build 3D printer extruders, specifically, something light that doen't require fabrication access (no milling, latheing (lathing?) 3D printed parts, etc.), just hand tools and such? I'm building a cheap 3D printer/wax CNC device, and the only problem I haven't fixed so far is the extruder, mainly becasue it will likely be fairly expensive (I'm looking for <$50, though), and thus I don't want to experiment more than I have to, as that will get expensive fast.
Im am new at this, can you spell out a few things for me,
If you were to try to make the brighest lamp why would you not use 4 of the leds and not use the droping resistors
How do you calculate the size (resistance and wattage) of the resistors if you were to use 1,2,3,4 of the led elements
The dimming circut you spoke about sounds interesting,can you give me more info on how to do that,or take the same aproach as in the led desk lamp #230 It seams to be a different aproach
That's 3 leds, and 1 heatsink (referring to parts list). Also, it would be fairly simple to add a dimming circuit using a MOSFET and the LM555 as a PWM controller. Good job..
Good Job Duffy ! Keep your thinking cap on...innovate or perish!
Regarding "dangerous" LED light; Anyone who works with LEDs has inevitably received 'retina burn' from looking directly at a lit source. Being an evolved human, the typical person quickly looks away to mitigate the effect....which is annoying at worst. (seeing spots)
"it hurts when I look at the sun"
"so, don't do that, stupid."
Here's a biological safety report from Lumileds for an LED comparable to the one John used. www.philipslumileds.com/uploads/292/AB81-pdf
Result: Low risk to damage the eye from white LEDs. I've read elsewhere that exposure to Risk group 1 is comparable energy-wise to looking at the horizon line on a bright sunny day at high-noon in the desert, without sunglasses. In other words, peanut butter is probably more dangerous.
That said, good call on the sunglasses/welding mask...those 'after-image' spots are truly annoying, especially if you're trying to work a solder iron!
Note: blue or royal blue LEDs present a higher biological hazard because of the narrow bandwidth and high energy content of blue light...so if you're developing a remote phosphor system or a weaponized blue LED stun light, keep your welding goggles handy.
In response to the nasty criticism about this being so very dangerous. Most of the readers drive cars, which are far more dangerous than this flashlight. Almost everything requires a bit of wisdom and good judgement to use. The safety rules designed to protect drunks bent on self destruction are a needless burden on most of society. What I am referencing is the european safety regulations for electrical equipment, by the way.
At some point an individual must take responsibility for the results of their actions, and a big part of that responsibility is understanding what one is doing. I know that is offensive to those who abhor personal responsibility, go ahead and be offended.
Those who produce my designs are confident in my level of responsibility, and know that I will not deliver a design that will not meet the project requirements. That would be a big risk if I were not responsible enough to assure that the design was adequate. Certainly there are many other engineers in a similar position, who are responsible for doing their job correctly. Those are the good engineers, the others need to have fifty people check their work for errors, oversights, and other types of goof-ups.
I disagree with the statement that Gadget Freak articles are just for novices. I'm a retired electrical engineer and I don't miss a single one. Even an experienced engineer can sometimes learn something.
For the most part, it is eye-safe. I wear sunglasses for the final test, and welding goggles while building becasue I am right next to the lights. More than a foot or so away, and it's not very dangerous for a short glance. Only when you are RIGHT on the LEDs does it really start to cause damage (I used a light-sensitive resistor and the threshold of a 3mW laser to determine what would cause eye damage).
Basically, if you don't have something right in front of the LEDs, and no one is looking directly at it, it isn't dangerous.
First off let me give John a thumbs up for the good work.
I have been reading this article over and over and cannot understand how Design News publishes a project that falls into a category of a flash light that can cause eye damage if looked at accidentally. This is not a novice project and Design News should considered not publishing projects of this type.
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