revised: am i figuring this LED power thing correctly?

[Jeff Shyu]

I swear this is one of those things that someone will link something in 2 seconds, because they know how to throw the keywords in the right order.. >_<

anyways. I'm trying to find a source to buy ~2 feet of FLEXIBLE acrylic/plastic rod, kinda like a fiber optic cable, except bigger.

the project is to make a substitute for something like this:



rather than moving the entire flash unit up to the front of the lens, I want to try out making a hood that goes over the flash surface, and 2-3 tubes that i can attach to the front of the lens, to simulate this:



figured if the stuff is cheap enough, it's worth a try.

edit: i already tried Mcmastercarr, but either i searched for the wrong keywords, or they don't have anything.

[Earl Merz]

I went through this just before I lost my job. Looking for "plastic" rod (.060 dia.). I can't see the pictures you posted, but I suggest looking for Monofiliment. Or Rod. There are quite a few places in SoCa that have this stuff in stock, but you need to know what material you are looking for and the size. When researching the polypropolene monofiliment I was looking for, I found places that that had plastic rod up to 5" dia.

I have no access to the sites or info I looked through, sorry.

[Doug Teulie]

Look for--->
LIGHT PIPE
FLEXIBLE

You can band it up to make a larger dia.


Some links--->
http://parts.digikey.com/1/parts/689302 ... r-305.html

http://www.freepatentsonline.com/5930442.html

http://www.ept.ca/docs/index.php?PageNa ... wMode=long

[Larry Andrews]

Best source for plastics that I know of is US Plastics. I helped build a bunch of 3x3x3 and 3x3x6 plating tanks with polypro sheet that we welded together - they had everything and could even get the nice euro stock for a reasonable premium. Dono if they'll have what you're after - but it's a good place and dirt cheap compared to most.

http://www.usplastic.com/" onclick="window.open(this.href);return false;

[Jeff Shyu]

follow up, though i have kinda changed the plan:

electrical savvy people, here's what i've got to play with right now, all bought from radio shack.

3.3v 7000mcd 25mA LED (i've got 2, but only using 1 to test right now)
battery box that holds (2) AAA batteries in series

when i connect the stuff up, it's not very bright. I didn't put any resisters inline, since i think it's actually a little lower than the required to power the LED.

do I stand to get much better output via 9v + 1/2w resistor? or am i pretty much getting what i'm gonna be able to squeeze out of the little LED?

[Jayson Woodruff]

What color is that? 3.3 must be white or blue. 7000mcd is 'fairly bright' for white and blue, but there are brighter out there. Usually the rated voltage is just barely enough to get the gate to open, then there's very little current left to drive the light. Two fresh alkaline will be 3.4ish V, mid life 3.0, end of life 2V. Rechargeable AA wouldn't even get there with just 2.

I'd say add another battery, or the 9V. You definitely should have the resistor in line. The resistor controls the current, without the resistor you can't be sure how much or how little current you're getting though the LED (except for a visual on the light produced).

9V - 3.3V = 5.7V, 5.7V/30mA = 190ohm, but will last on the order of 10hours. You're burning a lot of efficiency on across the resistor.

4.5V (3AA) - 3.3V = 1.2V, 1.2V/30mA= 40ohm. Will last on the order of 50hours

Don't worry about the resistors wattage rating. Even the inefficient method above is only burning .005Watts across the resistor.

Jay W

follow up, though i have kinda changed the plan:

electrical savvy people, here's what i've got to play with right now, all bought from radio shack.

3.3v 7000mcd 25mA LED (i've got 2, but only using 1 to test right now)
battery box that holds (2) AAA batteries in series

when i connect the stuff up, it's not very bright. I didn't put any resisters inline, since i think it's actually a little lower than the required to power the LED.

do I stand to get much better output via 9v + 1/2w resistor? or am i pretty much getting what i'm gonna be able to squeeze out of the little LED?

[Marshall Grice]

i'm suprised it's doing anything they way you have it hooked up.

go buy as close to a 228ohm resistor that is greater then .145 watt and hook it up in series with a 9v battery.

7cd should be decently bright.

edit:
Looks like Jayson needs to check his math.

[Jeff Shyu]

fancy resistor calculator here tells me that i need a 1/2W (RS has fairly limited spectrum of resistors) for 3.3v LED with a 9v battery.

the thing is, the LED package says : " FW supply: 3.3v (typical), 3.6v (max).

if i plug 3.6 into that same calc, i get 1/4W.

which should i go with (1/2 or 1/4)?

[Marshall Grice]

fancy resistor calculator here tells me that i need a 1/2W (RS has fairly limited spectrum of resistors) for 3.3v LED with a 9v battery.

the thing is, the LED package says : " FW supply: 3.3v (typical), 3.6v (max).

if i plug 3.6 into that same calc, i get 1/4W.

which should i go with (1/2 or 1/4)?

it doesn't matter. the .25 watt might get warm. the .5watt will stay cold. they'll both work fine.

using a 270ohm resistor isn't going to get you your full rated 7cd though.

[Jeff Shyu]

is 7cd more or less bright than your standard 6" maglight?

guess i'll stop off at RS on the way home tonight and get some 1/2 and 1/4W resistors and test them both out.

[Marshall Grice]

http://www.brightguy.com/products/Mini_MagLite_2_AA.php" onclick="window.open(this.href);return false;

the mini mag light is about 5cd. so yes it's roughly equivalent but probably a different distribution pattern.

if you're oging to go to radio shack just buy the .5watt and be done with it. you're not going to notice any difference performance wise.

[Jayson Woodruff]

edit:
Looks like Jayson needs to check his math.

Math was right, formula was wrong. (I^2 R or IV not I^2 V).


You can't 'over buy' a wattage rating on the resisor unless you're tight on space. I'd still use 3AAs over a 9V. But with the 9V and proper R choice you could run two LEDs in series without losing any run time vs one.


You get much better selection at mom and pop electronic stores over Radio Shack, and much cheaper. There's one here in Hunting Beach I'd recommend, but you'd probably pass ten good ones on the way. Maybe Marshall has a recommendation in the LB area.

Jay W

[Marshall Grice]

edit:
Looks like Jayson needs to check his math.

Math was right, formula was wrong. (I^2 R or IV not I^2 V).


You can't 'over buy' a wattage rating on the resisor unless you're tight on space. I'd still use 3AAs over a 9V. But with the 9V and proper R choice you could run two LEDs in series without losing any run time vs one.


You get much better selection at mom and pop electronic stores over Radio Shack, and much cheaper. There's one here in Hunting Beach I'd recommend, but you'd probably pass ten good ones on the way. Maybe Marshall has a recommendation in the LB area.

Jay W

i don't have anywhere special. besides jeff's project ADD is going to kick in before he kills the battery anyways so I don't think it matters how energy efficient he is. }:)

[Jeff Shyu]

speaking of project ADD, i still have a motorcycle sitting in my garage..

[Will Kalman]

Radio Shack: "You've got questions, we've got cell phones"

[Jeff Shyu]

once upon a time (this has got to be at least 14 years ago now), the RS sales people actually knew what they sold, and knew electronic basics.

I was almost going to ask the "saleswoman" what resistor i would have needed for the A23 battery, but the way her 2" fake nail curled around her fingers, and the phone glued to her face, i thought better of it.

edit: sometimes i miss working in newport, so close to costa mexico, where you can get wholesale anything, and marvac was right down the street.