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Led Inlays...


angry_jeremy
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I've been looking into putting LED dot markers in my next guitar and don't know what intensity would look right. The high-output kind (in the thousands of millicandella range) would prolley be too bright, at least I think anyway. I really have no frame of reference for what a 40mcd vs. 400mcd vs. 4000mcd looks like. What have people here used before? Any good pics besides from Sims LED? Pics of your own LED inlays?

Also, for those of you who have done this before, do you just make small wiring channels in the back of the fingerboard? I tried looking at the tutorial on LEDs but the like is dead (although I hear it was great... B) )

:D:D

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You should be able to dim the LED's with the right resistor. A larger resistor will lower the current through the LED and thus dim the amount of light coming out of it.

No clue what a mcd is. If it were me, I'd buy whatever is cheap and play around with it until it looks right. :D

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Having mucked about with LEDs while experimenting with effects pedals, I can suggest using a trimpot or the like to control the voltage to your LEDs.. That way, you can go for a bright one and then subsequently limit the brightness by using the trimpot as a sort of dimmer..

mcd is a unit of brightness?? :D Not 100% sure but I kinda recall that it is.. A candela or something like that..

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mcd is a millicandella (sp?), a unit of light intensity

can a regular-old 250K pot work for taming the current?

Jehle- the thing is that the kind of LED I get will dictate the resistor needed for the circuit. Obviously I don't need enough light to light my way in the dark like those LED flashlights but I wanna see 'em :D

Edited by angry_jeremy
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You'll have to experiment to find the right resistor for the level that you're comfortable with - once you've chosen your LEDs, calculate a resistor that will limit current to 20mA, and use that resistor (so you can't blow the LED) in series with a 1K pot or trimmer to find a suitable brightness with one LED. Then use your multimeter to measure the total resistance of pot and resistor (disconnect the LED and battery first), and round that to the nearest stock value. Use one resistor (with the calculated value) in series with each LED, and you're covered.

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So I need 2 values of resistors? One for the first LED, then 'X' others that equal the resistance of the pot plus the first resistor? Could I not just use the value of the pot "full blast" plus a resistor to act as the one master resistor for the series circuit? It would only be a matter of a little pluggin' and chuggin' with the calculator to figure out what pot+resistor combo would work.

What I would really like is to do more of an on/off control and not have to frig with pots at all. Ideally 2 circuits, one for the side dots, one for the fingerboard dots with a strat switch for side-side+top-top-off-off.

:D:D

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What I suggested was a test jig so you could choose the resistance that suited your needs in terms of brightness. Once you've found the correct resistance by adjusting the pot/trimmer in the aforementioned test jig, you can measure the resistance of both resistors in the test jig and use that value for each series resistor in the final setup. Or you can figure it out with a calculator, although I have no idea where you'll get the current vs brightness curves to do so. Good Luck!

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How many LEDs do you plan on running? Even if you run a 12 volt supply (say 8 AA batteries), the max you can run in series is 5 or 6, depending on what the forward voltage is. Besides, if you run series strings, any device failure shuts down the entire string, just like the old series Christmas lights.

It might be easier if you laid out your circuit design for us and asked specific questions about the areas that give you trouble. As is stands, we're pretty much going in circles.

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Geez, I didn't think it would take that much power to run such a small number of LED's... :D

Perfect case scenerio I would like to have 2 circuits:

1-side dots for frets 3-24, so 12 LED's all together (2 at the octaves)

2-front dots for same frets, another 12 LED's

Top it all off with a switch for Side, Side+Top, Top and maybe a master on/off for the whole shebang. I don't however want to have to have 2/3 of the rear of the guitar routed for batteries. I'd been thinking series circuits cause they seemed simpler but a parallel circuit could run more off just one battery, no? :D

Anywho, that's what I'm thinking. The only real problem with the 'guess and test' method mentioned earlier with the pot to control current is that I don't think I can get the LED's I want in town and would have to order them online. I don't wanna pay $40 for LED's that aren't going to do the right job if it's avoidable. See what I'm saying?

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:D Any LED will do the job, even that grab-bag from RatShack - I still don't understand what misgivings you have about the LEDs. You simply can't make a huge mistake, because anything will work!! It would obviously help if you had some idea of the constraints that govern the way LEDs function, but even without that, this is still pretty much a "pick yer size, pick yer color" situation. So long as you choose ones that emits visible light, you can't screw it up so badly that they can't be made to work!

And if you spend $40 on 24 LEDs (unless they're pink, or maybe lavender), you may officially consider yourself most heinously boned! :D

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might i suggest fiberoptic and a single led. or a multicolorone at least. it would seem simple enough by seem i got to see a warrior being done like that. so it was quite interesting.

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Jeremy, check here:

LSDiodes Optoelectronics

$.45US ea for 3mm or 5mm high intensity blues, and a flat $2.00 shipping "anywhere in the world". Same price for just about any color you can think of. They ship promptly, package well and even have freebie offers! Never pay more than a dollar for a single std. LED!

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I am curious as to how to power all these LEDs. Typical current through each one might be say, 10-20mA. Lets say you have them as 12 groups of 2 in series across 9V with suitable resistors, that will require 120 to 240mA. Thats a lot of current. Small 9V batteries give about 600 mAhours, but that is for depletion to half their voltage, by which time the leds will be too dim.

Im worried that the batteries wont last very long, maybe a couple of hours effective, unless you have more heavier batteries. - or rechargeables?

John

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i guess im doing a 6 one way half dozen the other way here, but to me it seems easier to run 27 volts with the LEDs in series and a single resistor.

That way you would only need 5-20mA total. Then all you would need is a single 1.5ishk ohm (1350 ohm at least) or more resistor, and the channel in the fingerboard would be easier to route.

you would need 3 9v in series to do that, but they would die VERY slowly.

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...it seems easier to run 27 volts with the LEDs in series and a single resistor...

Don't forget about each diode's fixed forward voltage drop. You can only run 8 blue LEDs in series from a 27 volt supply - with no resistor, you'll be running them at about 3.5mA each. If you add one more in series, the current drops to about 500uA each, because the diode string's total forward voltage exceeds the supply voltage, and none of them will light. If you use red LEDs, you can probably light 12 or 13 with fresh batteries, because they have a lower forward voltage. With 12, the current should be about 5.7mA ea, and with 13, it drops to about 1.5mA each, but keep in mind that as the batteries age, their voltage drops, so it's not going to be long before those current levels drop even lower. As soon as the supply voltage falls below the string's total forward voltage, they'll all go out. Also, if any device fails open, the whole string is dead.

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Lovecraft makes some good points about forward voltage drop and the number of batteries.

How about basing the idea on some AA size NiHm rechargeable batteries?. These have 1.2V percell, but unlike alkalines, then hold a much more stable voltage as they discharge, so you can set them up with a suitabel series/parallel arrangemet and then get a consistent performance, and be able to top them up when you want. They are easy to buy these days.

I think with 4 of them (4.8V), you could probably get 2 leds in series with a resistor, and have 12 groups in parallel. Lets say you go for 5mA of current in each, total current drain is 60mA. These AA batteries can hold 2000mAhours, so you could get 30 hours theoretically between charges.

You can get by with one resistor, put:

(12 in parallel) in series with (another 12 in parallel) in series with one resistor.

Does that sound like a design?

John

Edited by JohnH
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:D I guess it's fallen to me to play devil's advocate for this thread. The problem with using parallel strings of several LEDs with a single resistor is that in order to do it safely, you'll have to limit the total current to the safe level for a single LED. This is because, unlike a series circuit, where the current is constant throughout, in a parallel circuit, current takes the path of least resistance. This means that if you have several LEDs in parallel, the majority of the current is going to pass through the device with the lowest forward voltage, causing it to fail, which will transfer the current to the next lowest voltage, and so on, in what engineers call a cascading failure mode. It's always possible that all your LEDs might match close enough to avoid these problems, but the odds are up there with winning the lottery or being adopted by Angelina Jolie - the only sensible way to wire LEDs in parallel is to use a current-limiting resistor for each device. Sorry if I'm screwing up anybody's plans, but a reality check is preferable to having to do the job twice, at least where I come from. John's plan for running a resistor in series with two LEDs is the best idea I've seen so far.
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running a resistor in series with two LEDs is the best idea I've seen so far.

OK - so how about this:

establish a + and a - 'bus' as a pair of wires along the length of the fretboard. Between each of these bus wires, connect 12 sets of LED, LED, resistor. One each for the edge and centre of the fretboard at each fret marker.

It would allow another issue to be addressed. I have had LEDs of the same spec, but with very different brightneses at a given supply voltage. The pairs and their resistors could be tested and matched before installation. Individual resistor values can be adjusted if required. In fact make sure the whole setup works before installing it.

EDIT

another thought. make the resistors a bit low, so you get a somewhat brighter glow that you really want. Then put a switched wire wound pot in series with the whole lot, as an overall brightness control for different lighting conditions and to allow adjustment for battery strength, or to click the leds fully off!

John

Edited by JohnH
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