To Resist or Not to Resist

[Jhadious Aran]

So.. i know im not the only one or maybe i am but i was thinking if anyone else wanted to help out and make a quick chart on here for myself if not for anyone else on the "limits" of each LED or like an easier way to do a setup. instead of the common refer to the resistor chart or wiring diagram bf28 etc an idiots guide if you will. you could just refer to this thread or a thread that quickly shows you, such as

Red P4 + 4AA's +1000ma buck no resister = Works
Lux3 Blue +4AA's no resistor = no work
RGB Rebel + whatever = whatever

so on and so on? i dunno when im doing a saber and i want it overdriven looking at the resistor chart just doesnt help me. or lets say i tell my friend <insert random name> about making a saber and they just want to snapsnapsnap one together just to have one, Tim's made it very easy with the MWS now and im so happy for that. but then they say to themselves do i really need to resist it? sure there is trial and error i spose, and yes there are tons of ways to search or even ask, but if someone cant find the answer they're looking for on here and then they ask, there's usually some elitest that jumps in and just makes the person feel pretty crappy about the question they asked or makes them angry lol i've seen both here, and maybe its just me but are we not all here to help and for help? i dont know maybe i'm crazy for suggesting this who knows but surely im not the only one that feels this way? or would like to see something like that? heck i'd even take a chart i could print and keep by my lil desk that says hey man, if you forget to add that resistor in like you're supposed to you're going to pop that LED you just ordered, or hey did you know instead of using 4AA's you could use 1 (insert battery here) and get the same result? so on and so on.

Thanks for reading my crazyness.
Jhad

[TuxedoCartman]

The problem with what you're suggesting is that there are dozens upon dozens of battery configurations, each with their own voltages, out there; and in this store alone probably over 30 commonly used LED's, each with their own forward voltage requirement. That would be several hundred combinations to have to list. To make things even more annoying, technology can change in a hurry in this hobby; that's why there's still Luxeon III's listed in the resistor chart in the store. So even if somebody here feels like spoon-feeding the, well... lazy, then there's a good chance that the chart will be obsolete in a year or two's time. THEN you'll have people confusing the old red LED with the new red LED, and all you'll get for your efforts is blame for popping their bulbs.

OR... here's a better idea. How about people bookmark this free online resistor calculator (http://led.linear1.org/1led.wiz), learn to find the forward voltage of the LED they need to resistor, and figure it out on their own? It takes literally 10 seconds to do, from start to finish, and there's no chance of getting outdated info. In fact, I'd wager it's quicker to do it yourself, than to find it in a spreadsheet.

Also, and I really don't want to sound mean by saying this... but if a person can't remember to ALWAYS include a resistor on an LED when building a saber, then perhaps they should look at having one made for them. No offense, but that's kinda basic electronics 101 there. :(

[Jhadious Aran]

a lot of what you're saying makes complete sense, and i honestly didnt really think out every possible combination there could be with battery combo's, i was just writing what was on that crazy brain. however i have to disagree on the resistor part, by saying that if they cant remember a simple step to have someone make them a saber is kind of absurd. people in day to day living forget simple steps all the time. oh crud i left those dvd's in my car and i drove by the stupid drop box! etc. things happen, distractions happen, things can get overlooked. to say that if someone forgets one step that they are incompetant basically to put a saber together because they forgot/missed that 1 thing seems silly. to each their own i spose.

[TuxedoCartman]

Sorry... I've been in a foul mood all day myself. My bad.

Let me differentiate and clarify: forgetting to put a resistor on is understandable. You start putting these things together, and it becomes a tangled birds nest of wires and chassis parts and connectors; and depending on your build you may have to solder this to that, that to this, then run the whole mess through a tiny, tiny hole and hope that you can differentiate what comes out the other side, because now you're staring at two identical blacks and one red, then you get the whole thing messed up anyway because you are still stuck in economics mode, and thinking red is negative.... AAAAH!!!!

Yes, in that situation, forgetting to put a resistor on is totally understandable.

But forgetting that you need a resistor? I mean, it really is the part of the simplest circuit you can make. It's like forgetting a battery source, or the switch. Battery, switch, resistor, LED... that's as basic as it comes for a saber, and everything is built from there. Even when you start building Crystal Focus sabers with power-level indicators and multiple speakers, the concept's still the same: something needs to regulate voltage to an LED (it's just that the soundboard then takes the place of the resistor, though it does the same job).

So I will amend my prior statement to this: if you find yourself forgetting that you need a resistor for an LED, you're going to have an abnormally difficult time in this hobby.

[FenderBender]

One thing new builders can do is make a check list before each build. This way it's harder to 'forget' what you need. Also, having a chart like you propose would quickly become useless, like TC said. I also find it easier to memorize the formula for calculating resistance myself. It's pretty simple, and I am NOT a math expert.....at all.

You'll need the resistance formula (adapted for saber peeps): Source voltage - LED voltage X desired current = resistance needed.

[Johannes Huber]

As a feeely admitted new explorer in this artform I can say that TuxedoCartman is absolutely right about trying an LED resistor calcuator. It gives an amazing amount of info and allows for a great deal of exploring possible combinations of power source voltage, LED forward voltage and current without having to fry an LED or having one not work because there isn't enough voltage in the battery pack. The trick of it seems to be that when you look up an LED, there will be an area in the documentation with all the tech specs, you find its "Typical Forward Voltage", and check how much current you want to power the LED with (this will be measured in "mA"s in the documentation I've run across), and then decide what your power source will be, which will give you your "voltage" and then plug these three pieces of info into the calculator (at least the one I was shown by other TCSS members) and it will crunch out the numbers and give you the resistor you need and its color code bands (at least on the calculator I mentioned) and then you can go resistor hunting. That's what I've been doing so far and the only times it hasn't worked is when I solder something incorrectly or the like. You can also go the old fashioned route of figuring out everything through the Ohm's law but there is probably less likelihood for error with the calculator...
As always, if I missed something in the description of the process, hopefully someone with much more experience will correct me (in which case, I learn from it as well).

[Silver Serpent]

The rule is: "Always use a resistor." I'd like to make a small amendment to that. Always use *something* to regulate power. A resistor, a buckpuck, Petit Crouton, LED driver, etc all serve the purpose of regulating power to the LED. If you're using one, you won't need another. So there's no need for a resistor AND a buckpuck.

While you *can* build a simple stunt saber without a resistor by carefully matching your power supply to the LED, it is not a good idea to try this with more expensive components.

[Jhadious Aran]

LOL TC i hear ya, and i agree whole heartedly with what you guys are saying, think i was just trying to figure out a way to make some steps easier for some newbies when it cant be really made any easier, as it's already pretty darn simplified. one of those writing before thinking it all out type posts i guess heh, i'm just going to blame it on lack of sleep cause of the new kiddo! yeeeeeeah thats the ticket :P

Also i've never done a "sound" saber per se other than the cheapo board and i used a resistor with it, do you really not have to use a resistor/puck with the PC?

Thanks again everyone

** Also Johannes, which calc are you using?

[Silver Serpent]

You don't need a resistor or a puck with the Petit Crouton for the main LED. There's a fully featured LED driver built into the board.

You will still need resistors for any accent LEDs, illuminated switches, FoC, etc.

[Ashiva]

I think the point that is trying to be made is if the led is not connected to a resistor of some kind, whether it be a resistor, buck puck, or a driver board ( like a petit crouton or crystal focus) then its always safe to assume youre gonna pop it.

[FenderBender]

With anything that has a driver, i.e. The PC, buckpuck, TCSS driver etc, NO, you do not have to use a resistor for the *main* LED. Where you would use a resistor is for any accent LEDs like lighted AV switches etc. And yes, for stunts, you 'can' get away without a resistor, but there is risks and rules that you have to follow in order to get away with it. Resistor calculators are good tools, but trust me, it's quicker and easier in the long run just to memorize the formula. This is coming from a guy who HATES math.

[Jhadious Aran]

cool good to know for when i do my first PC saber.

Thank you

[Johannes Huber]

Hi!

I just PM'd you the link to the LED calculator that I was shown. I can't remember if it was here or on FX-Sabers where I found the original link in a post. My brain isn't working very well at the moment (I'm grading college final projects and dealing with a migraine at the moment. Hmmm, maybe I should wait to grade papers until I'm not having a headache, I'd rather like the students to pass the class...;) ) so I can't remember if I can post a non-sales related link and honestly, looking at the computer right now is... not fun so I'm not up to double checking. Hope it helps

Johannes

[TuxedoCartman]

Sorry, Jhadious... it looks like too many of us were resistant to the idea. Ha!!! Bad joke? Sorry... I couldn't resist. :D

[Ashiva]

I shoulda been more specific. What I meant was that a driver board usually acts as a resistor or normally already has one built in for the main LED ( I didn't wanna confuse him with main and accent talk but good point on the still needing a resistor for accent LEDs even when using a driver board) I'm just in a rule of thumb that the LEDs be connected to something other then just power (I e batteries). I'd rather do the extra step of throwing in a resistor ( if not using a board) just to be on te safe side of things. Like it was said, there are ways to get around using one, but personally I wouldn't risk it.

Haha!! I actually liked that joke cartman!:grin:

[Jhadious Aran]

@Johannes
Lol i hear ya, thank you very much for the link :)

@Cartman
ROFL nice

[Jedijigger]

I am NOT a math expert.....at all.

You'll need the resistance formula (adapted for saber peeps): Source voltage - LED voltage X desired current = resistance needed.

Your formula should read : (Source voltage - LED voltage) / desired current = resistance needed.

Ohm's law states R = V/I