Well, it's true that I have a specific point of view in this debate. True, since I've been teaching electronics and tend to be accurate, I personnally think that everything must be explained & detailed, but within a certain limit.
This is the "problem" : where to put the limit between no real information and the whole thing with mathematical equations...
My background, personality and the fact that I'm self taught for many things drive me to over expose and over detail things. There's however a difference between detailing and making things too complicated. There's also a difference between complicated and complex.
When someone says that something is too complicated, it can mean that he hasn't the right "educational level" (some times mis called "intelligence") OR... that it's badly explained or taught. So called bad students sometimes have bad teachers or unadapted teachers.
Now, my personnal problem goes with the people that "don't have time to learn more" because they "just want a lightsaber"... but they don't have the money to buy it ready made /commission someone to build it AND they want to try to build it anyway.
When you read a book about a certain topic (like "how to build you own vaccum formed machine"), you generally don't have shortcuts. If you buy this book just to watch picture but still think about doing it with a hair dryer, this is a stupid approach.
I'm then going to self moderate that by adding that some of us are teenagers, like 16 years old and, yeah, for sure, they're not attending university classes about quantum physics. I'm not putting everyone in the same basket.
Building luxeon sabers is hard. It's a complex mixture of electricity / electronics / wiring / soldering / anodizing / machining / threading / cutting / have-to-hands-that-work-properly-ing / common-sense-ing and some more.
It's fine if some of the list above is missing in your personnal skills. It depends how much you are ready to invest (time, money, research, work...) to fill the blanks and be able to get something nice.
Being accurate is one of this skill (personnal opinion). Using appropriate vocabulary is another.
On my side, I'd say that I used to overcomplicate things, but I'm trying to improve myself. However, I think that it's a waste of time to put an excel spread sheet on a webpage with 20 columns and 45 lines to give a pre calculated resistor value for every luxeon combination of model / current / batt pack solution. This is not teaching and this is not sharing knowledge, it's exactly the oposite.
It's give the impression to be sharing while you answer 2% of the question.
then, the user might use well this spreadsheet, but will wonder a month after which resistor to use with a little 3mm and not a luxeon. Or the person will simply use the same resistor without thinking that it will pass 1A into a little led that accepts 100 times less and the customer is REALLY surprised of the smoke and smell he gets...
Now look in my user's manuals. Probably they need to be rewritten with better english and better pedagogy aspects but... I give the general way of calculating things, and I add an example to it. Then it's rare that I get a question, or sometimes, it's just to confirm that the result is ok.
The other point is that forums and email are just unadapted tools for what we are exchanging here. Let's be honnest and what how the thread goes, it slips on oil (or mud... or worst - same color- ...) in 2 secs... simply because it takes SO MUCH time to take precautions in this informal media so that info isn't mis interpreted. That's why I'm also now self documenting my work in articles (equivalent of a sticky on a forum) once the summary and formatting of info is correct.
NO, there isn't GENERAL RECIPE that will always works with the plurality of devices we are using. Don't try to compare things that are different.
Now about a few points that have been discussed here, and so that you can be rewarded to read all my poetry :
- terminology / simplification : I agree with eandori. Specifically on the "luxeon is like a resistor". First thing is that it's incorrect and second it's not a "pedagogical simplification" that would help. Sometimes a metaphor or comparison, although not totally correct can be helpful for explaining something, but it's not the case here.
LED are a semiconductor. Semiconductor isn't related to a person driving half of an orchestra. It's an ACTIVE electronic part, as opposed to a PASSIVE one, like a resistor. An ACTIVE part needs power to work.
The LED is a diode, specific in a sense that it emits light (visible or not). LED = Light Emitting Diode. The reaction of LED are linked to a curve relating current to voltage. It's totally non linear, and is basically almost no current until a threshold, then an exponentially rising current as soon as you just increase a bit the voltage. That's why the slightest mistake on the voltage applied to the LED will "open the gate" and let a HUGE current thru it.
That's basically where the statement "the LED eats what it wants / need" comes from.
- LEDs must be current driven. A static or dynamic system must servo the current in the electric path. When voltage is constant (provided by an DC adapter plugged on the mains for instance), it can be as simple as a current limiting resistor. The resistor will absorb the difference between the wallmount adapter voltage and "the voltage at which the LED goes for a specific current" and will transform this excess of voltage into heat.
- current regulation : most of the drivers we are using (as the topic title says : no resistor here) are doing a step-down conversion (buck converters). If the voltage of the batteries stay above the threshold voltage of the LED (what is called the forward voltage), current is lowered and averaged by a chopper (no helicopter in that thing). To limit the current, power is applied for a certain time, then shut off, and so on, periodically. The smoothing is made by a coil, or self-inductance, generally this winded copper wire part (wire is winded around a ferite pot/core) that is just next to the luxeon output.
The time during which the power is applied changes over time, and increases while the batteries are going down.
- step up converters (or boost converters) : another system that fights the fact the batteries provide a voltage lower than the forward voltage of the luxeon. Thanks to the ohm low ( U = R x I), you can increase the provided voltage but it will suck more current. For achieving that goal, energy must be accumulated before being released, still using a coil, since it's a current accumulator.
As an example : think about the gear system of your bike or a middle age crossbow. The latter was impossible to arm by hand, you needed to spin a mechanism. With a lot of turns (current), the rope was getting more and more tight, energy is accumulated, then released (the arrow is released and moves, it's equivalent to a difference of potentials, or voltage)
Advantage : current is provided almost until the battery is TOTALLY empty.
Those converters / drivers are not so popular in saber technology because they use more current, autonomy will be reduced, but it's a nice way to light up a lux V with a low voltage battery setup.
On the other side, it's VERY popular in the flashlight world, where the idea is to suck all the juice of the battery instead of getting it dimmer and dimmer as soon as the threshold is reached.
- SEPIC converters : it's one possible topology for making a buck-boost. No easy to make / design, but some flashlight have that. It can start by doing a step down operation, then when the voltage isn't enough "turn into" a step up converter. For instance, my ultrafire C3 flashlight accepts 1.2 to 4.2 volts to drive a white luxeon (forward voltage generally around 3.7v). It therefore works with a AA rechargeable ni-mh, or alkaline, or 14500 li-ion (3.6v / 900 mAh, same form factor as a AA).
- why not HOT SWAPPING luxeon on crystal focus.
Crystal Focus is doing step down current regulation. To my knowledge, it's the only board that dynamically synchronizes the sound duration to the power up / power down ramp effect of the blade with the accuracy of one sound sample.
Current regulation with instant start are very simple cause they don't have to ramp the current and monitor it at the same time. The servoing is much more simple.
In my case, I have to remember, when the saber is off what the state of the batteries are. Just like diodes, batteries are not linear for current available versus measured voltage. When I power up crystal focus IT CAN'T KNOW how much juice the pack can provide, and therefore CANNOT calculate a ramp duration to match the sound duration. That's why the first ramp is generally not accurate in duration.
Once the battery juice has been measured once, I have a "target" for the current servoing for the connected luxeon. The second power up will be smooth and accurate in duration with the sound. Change the luxeon while the blade is off (but power still applied to the board), and you **** UP the whole thing. I naturally payed attention to that when playing around myself, but eandori is the one who tried... and fried (I owe him a beer for that).
that's why it's now written in B&W in CF user's manual.
I know, that was long but... you now know me as an academic b@stard
Erv'
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Originally Posted by xwingband
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