# Power Supply

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Does anyone know what is typically used for guitars with LED inlays? I am plannig on putting in some LED's for the side dot markers. After doing some calculations, the power consumption looks pretty nasty. Unless I did them wrong, the battery will drain quite quickly.

So I was wondering if anyone has ever seen one / owned one and could tell me what type of battery (or batteries) is normally used.

The SIMS site doesn't seem to provide much info on what is actually put into your guitar and I'm not aware of any other companies that do this.

Thanks,

Dave

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I've got no experience of the real thing, but I'd say 2 9v batteries in parallel should do the trick.

I did some calculations on this stuff to see what you could have come up with, and I found LEDs which required 20mA of current. Assuming you've got 12 LEDs (one for each "dotted" fret, two on 12 and 24), that means a total of 240mA current. A normal 9v battery gives 580mAh (according to the EMG website), which should then last about 2.5h. It is however very much possible that I've overlooked something.

What would you use this for? If you're going to use it when practicing, I can see it would be a bitch to change batteries that often, but if you're only going to use it when gigging and such, I can't really see the problem.

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There are a bunch of ways to approach it -if you use superbrights, you can dim them (especially whites and blues), or use a constant-current source set well below the max. Using a parallel array with a constant- current supply will let you get reasonable battery life from a 9 volt - 6 D cells would last a lot longer. Check this site out( OddOne's White LED Information) for basic concepts and homebrew info - he's even got a setup that'll drive a single white LED at 20mA with a single AA cell. Or type "LED circuit" into Google and wade in - there's more info out there than you can ever absorb. Here's a simple circuit for a 24 LED lamp that you could easily adapt to 12 for your marker system.

The brite blues I experimented with were extremely bright down to below 9 mA, so you've got some wiggle room - when they start to dim, replace the battery. Id' also recommend an off switch, so they're only on when you want them to be.

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Thanks for those great replies.

G_urr_A - My calculations predicted a similar result. I was also looking into those "medical" 9V lithium batteries that have a rating of 1000mAH but I'm still looking at a number of hours before the batteries need to be changed - not days.

lovekraft - Thank you very much for all of that information. I am planning on using blue LED's. I bought some and can't remember the specs on them. Are all blue LED's considered super bright? I think mine are because they are very bright. I have a 22 fret neck so I'd only be using 10 LED's. I will see if I can make sense out of that circuit you have shown. Do you remember where it came from? Is it from the OddOne site also? I have been doing google searches and have seen many sample circuits but not much in terms of calculating battery life.

Thanks again. I'll look into the dimmer circuits and alternative batteries.

Dave

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OK, I have found some more info on battery life. I didn't realize there was such a big difference in mAH between a 9V and something like a AA battery. It looks like I should consider going with something other than a 9V and I can get big increases in battery life. The main reason that I wanted to go with a 9V was due to the fact that I can get battery boxes easily. With something like AA's, I will have to make something up myself or put them in the control cavity.

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my friend was gonna put led's on her neck, but on the front dots! how would this be done? (i mean drilled in without hitting to truss rod!)

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Whisky, the consensus was that you'll have to remove the fretboard and work from the back. Check these threads:

Dave, I can't for the life of me find the page I found that circuit on, but here's the text I attached to it on my computer, hope it helps:

The MOSFET current source can be any N-channel enhancement mode unit designed to be driven by "logic level" signals. It must fully turn on at 400mA with Vgs<3V. Beware of static electricity on the gate of this unit! I destroyed the IRLZ34N used in the breadboard when I soldered it into the actual unit. A small 1" square of sheet aluminum serves as a heat sink. Dissipation is about 0.9 watts at maximum current with a true 6V worst case source.

R4 samples the LED current. Voltage drop is 0.2V at 400mA. If a much larger or smaller array is used, R4 should be adjusted to give ~0.2V drop at maximum array current (~20mA/LED).

Q1, D2, R3, and R6 form a simple "single supply" op-amp that can sense the voltage across R4 nearly down to zero volts. The forward voltage drop across D2 is nearly identical to the base-emitter drop of Q1, thus the voltage between the arm of R2 and ground is the same as the voltage across R2. D2 provides nearly perfect temperature compensation for the dimmer control, which becomes very critical at the dimmest settings.

R5, and D1 provide a regulated voltage for the dimmer control R2. This voltage, about 0.5V, is not temperature compensated, but is not critical in this design.

If R2 is set to max current, 0.2V will appear on the base of Q1. The collector current of Q1 will be momentarily be cut off, which will turn on the MOSFET. The voltage across R4 will rise until it reaches 0.2V, giving an array current of 400mA. Q1 will then turn on, regulating the array current.

R1 is the only critical part. R1 must be chosen to provide the desired maximum array current at the maximum setting of R2.

The drop across the LED array is ~3.5V at maximum current. As the batteries die, the drain-source voltage of the MOSFET gradually drops to zero, and regulation is lost. The lamp will gradually dim, but the MOSFET will stay locked ON, with the only wasted power being the drop across R4. Dimming the lamp will bring it back into regulated mode for a while. This circuit extracts nearly all of the energy in the battery pack, down to 0.75V/cell for a 4-cell pack.

The ~25mA minimum array current results from slight differences in the forward voltage drops of D2 and Q1. If desired, replacing D2 with the base-emitter junction of a second 2N2222 should reduce the minimum current to ~zero.

Wish I could credit the original author, but I was just grabbing stuff at random, and I didn't document the source, so apologies to whomever did the original work.

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• 4 months later...

personally i have used rechargable lithium batteries.. somethign like 3600ma hours at 3.6v from ratshack. killer little bats

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