A Lux V question I haven't seen directly answered

[Kamurah]

Outstanding....

Thanks for the help and info.

Cheers

[Steeljack]

I would say you should use a resistor for the voltage drop to the mr board because a buckpuck is a luxeon driver not an adjustable voltage regulator. So calculate 5v for the mr board and just find out what resistor will drop 7.2 to 5 or 4.5 for the board then splice the batt pack wires over to the buckpuck for the led or however you do that part.

How exactly do you propose to make a resistor act as a voltage regulator?

If you attach one leg of a one-megaohm resistor to the positive lead of a 7.2-Volt power supply, you will still measure a voltage of 7.2 Volts on the other leg. (You'll be able to pull a vanishingly small current through it, but it'll still be at 7.2 Volts.)

You could try to create a voltage divider, but voltage dividers are really only good for sensing currents. The moment you put them under load, as the article notes their voltage tries to wriggle out from under you.

[Eandori]

One problem I see is this...

The Buckpuck going to the MR board is not so much a soft limiter of 700mA but it will TRY to drive 700mA as hard as it can. If the MR board is for some reason taking less current then that, the buckpuck would respond by pushing the voltage input higher to attempt to maintain that 700mA.

So if your battery supply going into a buckpuck was 9.6v, and your MR board really only needed 100mA to drive the speaker, then a worst case scenario would be the BuckPuck pushing slightly less then 9.6v to the MR board in an attempt to reach the rated 700mA.

So I would not hook up a buckpuck like this unless the MR board was ok with BOTH restrictions....
MR board can handle up to 700mA
MR board can handle input voltage of 7.2v if it was using less then 700mA

My kneejerk reaction (without any data) would be to guess that just an MR board with a speaker would not use 700mA. I figured those speakers were closer to 1 watt with the board itself only dissipating like .1 watts. a 5v input on the MR board and 700mA is closer to 3.5watts of power being "shoved" into a device. Seems like too much.

One easy test would be this... Hook up a DMM in series with your MR board to a known safe battery voltage. Measure the min and max or at least average curren that board uses. Try not to exceed that.

[pipster79]

my sugestion is to go to radio shack and get a 5v voltage reguator there very small, bout 7mm square or smethig like that i think, easy to wire up, 3 pins, 1 is ouput 5v, one is groun, and one is input max 32v i think it is, that will protect ur mr board, and there only around 5 bucks, mayb when i get back from dinner ill find a link so u can c it for uself.

only one thng about it, when the voltage drops below 4.5v input, it will stop putting out voltage. ie u will stop getting sound till u recharge the battery pack

[Kamurah]

ok...so....

BOTH the 700mah and the 1000mah BuckPucks have a control voltage REF pin of 5v....

So....theoretically.....could I use just ONE 700mah Buckpuck - wiring the LUX V to the LED output pins and the REF pin to the MR Board with a 7.2v power supply?

I suppose I would still need to measure the current draw from the MR board to make sure the current flow wouldn't be too high right?

[Steeljack]

ok...so....

BOTH the 700mah and the 1000mah BuckPucks have a control voltage REF pin of 5v....

So....theoretically.....could I use just ONE 700mah Buckpuck - wiring the LUX V to the LED output pins and the REF pin to the MR Board with a 7.2v power supply?

I suppose I would still need to measure the current draw from the MR board to make sure the current flow wouldn't be too high right?

Ergh. Probably not. I just did what I should have done before shooting my fool mouth off, and checked the datasheet for the BuckPuck.

While the REF pin does indeed provide 5V, it's only guaranteed for up to 20 milliamps. While that's adequate to drive a microcontroller or other small component, it's not going to be anywhere near enough to provide you with sound.

That means that pipster79's got the right idea: you'll want a separate voltage regulator.

The good folks at Spark Fun have a couple of different regulator ICs you could use to this end. The LM7805 seems like a good choice: 5 Volts, and more than enough amperage for your purposes.

The spec sheet suggests placing capacitors between the pins, but in any case it ought to be fairly simple to build into a circuit. (Feel free to PM me if you want to delve into the grotty details.)

[pipster79]

use a regulator, u dont need to worry bout current going to the mr board only the voltage, so just go to radio shack and get a voltage regulator for 5 bucks, much easier then trying to figure out how to wire a buck puck to do the same thing

[pipster79]

oh and if u must know the output of the 5v voltage regulator is 1a, but its totaly safe for the mr board, i have one in my anakin saber and it works fine

edit, steeljack thats the one i was talking about but rather then wait to order it from some place online u can just walk into your local radio shack (or "the source" as its called in canada) and pick one up

there nice and small but very easy to work with, and no need to worry about figuring anything out like amperage or what not, and u dont need capacitors between the pins, those diagrams were for different models and for different configuations, if using it just as the positive regulator that is its primary pourpose u only need wire the output + to the mr board and the input voltage and ground from your battery pack, u can run the groud from the battery pack straight to the mr board. or what migh b easier is wire the positive and negative from the mr board to the regulator and then the positve and negative from the battey to the regulator, either way works fine

[neophyl]

You definately do NOT want to use a puck to drive the MR board. You do want a 5v regulator like Pip mentioned. They come in a variety of sizes and ratings, from 100ma, 200ma, 500ma (which will drive a MR fine) and the 1A and even 2A versions.
It shouldnt cost more than a couple of $ and for this application you wont need the smoothing caps really although if you want to add them then fine.

About the 5v from the puck, besides it being only 20ma of current output you couldnt use it to drive the mr board properly anyway even if there was enough current. See when you switch the puck off power will be lost to the MR board immediately which means no power down sounds.

[Novastar]

Excellent comments everyone...

One last thing I can add is... you MIGHT want to add a small heatsink to the voltage regulator if it ends up shunting off quite a number of volts. It will get REALLY hot.

Corbin did this for one of the BOP I sabers, and as near as I could physically test and tell... it was certainly needed. I might be wrong but... 2.2+ volts seems like an awful lot of heat, and MAN did the voltage regulator get hot!

This may have been because he had to place the regulator RIGHT next to the FX board... and we didn't want to kill it with so much heat.