Wiring an LED bar graph array?

[Matt Thorn]

Its a circuit, it makes no difference what side the resistors are on. The total resistance stays the same.

Thanks. Learn something new everyday.

[Matt Thorn]

You calculate the resistance based on the total [required] current of all 10 LEDs. 10 LEDs x 25mA per segment = 250mA. With just a single 150ohm resistor, you were still only feeding 20mA to 10 LEDs (IOW 2mA per LED ). If you're going to power all at once, try a 10ohm 2W resistor.

Thanks. Ohm's Law, right? Perhaps if I had been fiddling with that in the morning, instead of late Christmas night after a couple of beers, I'd have figured that out for myself. Yes, soldering under the influence. Darth Tyranus would slap me upside the head.

[Matt Thorn]

that is COOL, and the saber looks like one of do-clo's, but I could be wrong, and idt does look mhs doable.

DoClo made a pair of sabers in this style for a customer. But the non-functioning replica pictured here was made by someone else, and is much closer to the actual prop (also pictured on the Saberwiki page linked above).

[Matt Thorn]

Well, what I would do is to run it in parallel with the LED. If you are using an ultrasound or other driver the resistor calculation is made a bit simpler.

(Main LED Voltage - LED bargraph voltage)/Amps = resistor value

I'd recommend 100mA (or .1A for the calculation) to the whole bargraph.

If you don't have a PSU to test the main LED just meter it once setup or take the average value from the specs.

Just when I think I'm getting close to Intermediate level, one of you veterans reminds me just how much of a Beginner I am. I'm afraid that whole post went over my head. I am in fact planning to run it parallel to the Luxeon III. Does that mean the crude solution I worked out here won't work when put in the same circuit as the Lux? And what's a PSU? I'm guessing it's not a reference to my alma mater.

[xwingband]

Oops... PSU is a power supply unit.

The way you have it wired is fine really. If you didn't measure the LED value though it will likely be dim. See... a driver like the Ultrasound gives out whatever voltage the LED needs. That's called "stepping down".

So I'm not sure what voltage you lit it with in that photo but it's not likely to be what the board gives to the LED. So if you have a multimeter I would check that. Or the simplest thing is to use an average spec. For III's the average is 3.9V for whites, green, and blues, and 2.95V for Reds and amber.

(Bonus! If your LED only needs 2.95V and the bargraph say needs 3.3V... don't worry about the resistor! It will regulate itself.)

Also I'll explain the parallel setup. For the bargraph it will be the positive from the board (same as Lux III), and the negative from the battery directly. This will make the bargraph mirror your main LED for all the lighting effects.

[Matt Thorn]

Oops... PSU is a power supply unit.

The way you have it wired is fine really. If you didn't measure the LED value though it will likely be dim. See... a driver like the Ultrasound gives out whatever voltage the LED needs. That's called "stepping down".

So I'm not sure what voltage you lit it with in that photo but it's not likely to be what the board gives to the LED. So if you have a multimeter I would check that. Or the simplest thing is to use an average spec. For III's the average is 3.9V for whites, green, and blues, and 2.95V for Reds and amber.

(Bonus! If your LED only needs 2.95V and the bargraph say needs 3.3V... don't worry about the resistor! It will regulate itself.)

Also I'll explain the parallel setup. For the bargraph it will be the positive from the board (same as Lux III), and the negative from the battery directly. This will make the bargraph mirror your main LED for all the lighting effects.

Thanks. I'm pretty sure I got all that. I'm thinking of using this with a blue Luxeon III, so I suppose I'll need a resistor. The Ultrasound 2.0 allows you to set the LED you're using. I wonder if the "Luxeon III Overdrive" setting would compensate for any dimming effect? BTW, in the photo I have the LED bar alone attached to a 4aaa battery pack, without a driver or Lux, which is probably why it's so bright.

[Matt Thorn]

Oops... PSU is a power supply unit.

The way you have it wired is fine really. If you didn't measure the LED value though it will likely be dim. See... a driver like the Ultrasound gives out whatever voltage the LED needs. That's called "stepping down".

So I'm not sure what voltage you lit it with in that photo but it's not likely to be what the board gives to the LED. So if you have a multimeter I would check that. Or the simplest thing is to use an average spec. For III's the average is 3.9V for whites, green, and blues, and 2.95V for Reds and amber.

(Bonus! If your LED only needs 2.95V and the bargraph say needs 3.3V... don't worry about the resistor! It will regulate itself.)

Also I'll explain the parallel setup. For the bargraph it will be the positive from the board (same as Lux III), and the negative from the battery directly. This will make the bargraph mirror your main LED for all the lighting effects.

Wait, I said I think I got all that, but I didn't. The specs on newark.com say the array has "Forward Current:25mA", "Forward Voltage:2.6V". But I don't know if that's for each LED or the whole array. This is where the fuse in my tiny brain gets close to blowing. Is the number of LEDs irrelevant?

Forward voltage of the blue Luxeon III: 3.9v
minus
Forward voltage of array: 2.6v
equals 1.3v
...
divided by 0.1 amps...?
...
equals 13...ohms...? And the resistor wattage would be...

Fuse blown. Time to go watch the Teletubbies and eat dry Cheerios.

[Sairon]

This saber could be done also with a 1.25 sinktube, 1.25 blade holder, and hardware stuff over top

[eastern57]

Matt, the specs provided apply to each segment - each LED requires 2-2.5V @25mA. So if you run all the LEDs in the bargraph in parallel, that means the current requirements get added up - 250mA total. The voltage requirements stay the same.

What Xwing is refering to with the US, is the voltage is adjusted automatically, and feed what the LED requires - so you don't need to worry about that - just pay attention to the current requirements.

I've wired up accent LEDs with an ultrasound (just like he described), and you'll see that with that much required current, you won't need a resistor anyway.


... and last thing, Matt - multi-quote & edit buttons are your friend

[Matt Thorn]

This saber could be done also with a 1.25 sinktube, 1.25 blade holder, and hardware stuff over top

I'm debating whether to do it that way, or fudge it with MHS parts. Carving out the decorative "gullies" on MHS pieces could be beyond the capacity of the equipment I have, but dremelling a sinktube and laying it over a basic MHS hilt with a black matte finish would fairly easy.

To top it off, I'd like to use that LED array as the switch, probably improvising a momentary pushbutton switch with a couple of springs and a tactile switch. Sounds like I'm biting off more than I can chew, doesn't it? The alternative is finding some way to improvise a momentary switch (pushbutton or rotating) from one of the two big silver thumbscrews. (BTW, I found thumbscrews of just the right size and shape online. I think. DoClo says he custom machined the ones on his Adi Gallia sabers.)

Then there's the whole problem of the blade holder. I'm thinking of just asking Tim to custom machine one for me. And since I've ordered a Craftsman Powder Coating System, I might try powder coating the blade holder (Xtreme Chrome and Sun Gold) myself. As for the pommel, I think the MPS pommel style 4 will do, though it's actually rather shorter than the real thing.

I've derailed the thread. Sorry 'bout that.