I bought this novelty spinning LED light thing. It runs on 3 AA Batteries (1.5v x 3 = 4.5 volts total). I want to hook it up to an illuminated 12v switch, so that when it's on, the switch lights up. This works great for my 12v stuff. but since it's 5v, I can't use my lighted switch.

What I would like to do, is hook the switch to 12v, so the light in the switch works, and hook up my 4.5v (5v) light to it. I think what I need is to put some resistor(s) on the + side of the spinning light to get it down to 5v. Can someone help me out here and tell me what resistor I need, and some tips on using them?

Thanks, I hope to have some pictures posted this weekend of my project. It's taken me about 4 months to complete. I'm looking forward to showing it off.

you need to know amperage draw of the device to calculate the resistor you need. a regulator would work too but that is alot of part (reg plus 2 caps) for just a spinning led thing

I think you would have to use a 7805 voltage regulator.

You're exactly right -- some resistors on the + side of the lights should do just fine. You'll have to calculate what values (both Ohms and Watts) to use for the resistors.

Jonny English had a good writeup for Math for LED Arrays about a year ago. Also, one of the most widely-used online calculators is at Methku Mods.

If you have a multi-meter, you'll want to measure the current being used by the LED's (while the LED's are lit, touch one lead to the + of the battery and the other to the -). This'll give the number of milliamps you'll need in your resistor calculations.

If we can give any more help at any step along the way, feel free to ask!

EDIT: I was thinking it was straight-up LED's, but after rereading your post, j-dogg may be right... Depending on the circuitry used (Is there a motor that makes it spin?), you may need a voltage regulator. To find out, measure the current that it's using. If it stays the same the whole time it's running, you can probably get away with resistors. If the current goes up and down during its "light show", you may need a regulator.

Looks like I'm gonna be losing my pretty illuminated toggle switch

I don't know enough about voltage regulators to make that work.

Someone correct me if I'm wrong, but if the current draw is constant, resistors should work fine.

Do you (or anyone you know) have a multimeter? It's a good thing to have around anyway for modding. I got mine for $20 at Radio Shack, but I've seen budget ones under $15.

Quote: Originally Posted by FunkyFresh Someone correct me if I'm wrong, but if the current draw is constant, resistors should work fine. Do you (or anyone you know) have a multimeter? It's a good thing to have around anyway for modding. I got mine for $20 at Radio Shack, but I've seen budget ones under $15.

I have a Fluke. I'm no expert in using it though, I mostly use it for measuring AC and DC voltages and checking continunity. This thing normally runs on batteries. how do I go about measuring current draw?

Thanks everyone for helping.

It should have a setting for current, or milliamps (mA), or something similar. If it has a setting for 10 or 100 milliamps (or if it just has a single setting for DC Amps, like an A with a solid line), that should work.

If it's just some LED's in series, then the reading will probably be 20-30 mA. If it has a motor and other components, my wild guess is that it'd probably be more like 100mA.

I'll attempt to measure it tonite and post my results. I am assuming that I just hook it up to the + and - wires coming from the batteries. I'm also going to try to run my 12v illuminated rocker off of the 5v wires and see if it still lights up. This project is actually for a child, so I'm ok if it isn't super bright. you likely won't be able to see it anyway with all the other "bling" going on.

I also had the bright idea to just try to find a 5v illuminated rocker switch.

you can use the 5Vdc output of your powersupply.
It has 5 outputs -12v,+12v,-5v,+5v,-3.5v (check table on side of powersupply case)
I believe its the yellow and black wire, that should give you +5VDC output

Maybe some soldering involved.
If you've got a multimeter just measure between the different wires(molex).
Black is always ground, red is +12v lead, yellow is +5v lead

Quote: Originally Posted by Lite_User you can use the 5Vdc output of your powersupply. It has 5 outputs -12v,+12v,-5v,+5v,-3.5v (check table on side of powersupply case) I believe its the yellow and black wire, that should give you +5VDC output Maybe some soldering involved. If you've got a multimeter just measure between the different wires(molex). Black is always ground, red is +12v lead, yellow is +5v lead

I thought the red wire was 5v. unless I'm not thinking of the same thing you are. and I thought all the black wires went to the same ground. I even checked this with a continunity tester. I'm no electronics expert though, so these things may only be correct in my head.

You're right, Nexto, the red is +5V, yellow is +12V.

Lite_User, the problem with running it at 5V is that his illuminated 12V switch probably wouldn't light up. But yes, it would be fine for powering the actual spinning LED thing though.

Quote: Originally Posted by FunkyFresh You're right, Nexto, the red is +5V, yellow is +12V.

Woohoo I'd learneded something!

Sucks being at work when you want to be home xpera'mentin.

Sounds like a job for a relay - a bog standard 4 pin auto one would do the trick.

Hook up a black wire from the psu to one side of the relay coil, and a yellow one (via your switch) to the other; connect a red wire to one side of the switch side of the relay & a wire from the other relay switch pin to the +ve side of your spinny device, and a black wire from the psu to the ground side.

ok i know resistors are pritty simple, but if you dont want to find out the amps, you could just wire up a relay, that is triggerd bu the 12v swich, and activates the 5v led spinner

i know it is not the best thing, but every thing else i could hve said, has been, but my recomendation, is to use a vreg, just because it can keep a constant current

Quote: Originally Posted by Cpl Rampage ok i know resistors are pritty simple, but if you dont want to find out the amps, you could just wire up a relay, that is triggerd bu the 12v swich, and activates the 5v led spinner I know it is not the best thing, but every thing else i could hve said, has been, but my recomendation, is to use a vreg, just because it can keep a constant current

I'm not against using a voltage regulator. I'm just not fimiliar with them. It sounds like the right tool for the job. The relay is an interesting idea too.

I think I'm gonna try to hook it up normally using the 5v and see if the light comes on (I doubt it will). If that doesn't work, I'll get the measurments and post here and see if someone can tell me what resistor to try.

If someone can explain the voltage regulator to me, and how to hook it up. I'ld love to try that too.

how do I know what voltage regulator to use, will it say it converts 12v to 5v or something?

Thanks again for all the great advise.

Quote: Originally Posted by FunkyFresh You're right, Nexto, the red is +5V, yellow is +12V. Lite_User, the problem with running it at 5V is that his illuminated 12V switch probably wouldn't light up. But yes, it would be fine for powering the actual spinning LED thing though.

hey guys

but maybe he can use the conntactor from the switch itself
and if he switches it what does it supply?

it is possible to relay the 5volts through the switch itself and so light the LED's
but offcourse the question was was does it connect or supply.

Grtz Lite_User

OK, Here's what I ended up with. I was able to get the illuminated switch to light on the 5v circuit (Dim, but lit) and was able to power the 4.5v device with 5v no problem. The thing really looks cool. If anyone is interested, it's called a whirligig LED spin light and they are only sold at Spencer's Gifts (usually found in a mall). I can't even find one of these on the internet, or Spencer's gifts website. They cost $7.99

I'll hope to post some pictures this weekend if anyone is interested.

Thanks again for all the help.

why don't you try using a 2k pot, start at max resistance, and slowly reduce it until your spinning wheel lights up?

if you don't want to mess with resistors or a pot, use a 7805 regulator as already suggested

It has 3 pins, Vin, ground, Vout. Connect Vin(1) to your 12v, ground (3) to ground, and vout(2) provides 5V

+5V Fixed-Voltage Regulator 7805

$1.59 Catalog #: 276-1770 for radioshack

You could also use an LM317, but it's a little more complicated.