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Author Topic: Help with LED flashlight circuit design  (Read 7091 times)
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John Welden
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« on: April 20, 2013, 03:24 PM »

I'm sort of toying with the idea of fitting a tiny LED into a ring that you'd wear on your finger. I've found miniature hearing aid type batteries and an LED small enough to fit inside a ring.

From what I know, all you need is battery, resistor and LED to make light.

The batteries I found are in the 50 to 100 mA-hrs range. I don't really understand what milliamp hours means for what I want to do other than bigger is better.

I don't understand what the resistor is for or how big it needs to be. Do they make miniature resistors? How do you figure out which one you need?

I found small enough LEDs to fit in a ring.
Examples:
http://tinyurl.com/cwu4d8c
http://tinyurl.com/bqlbqyf

I don't understand the luminous intensity rating.  Is 90 enough to do anything useful? I don't expect this thing to put out a lot of light, but hopefully enough to like read text on a page or something. Hopefully the battery(s) could last more than a joke amount of time?

I have no idea what I'm doing, just trying to learn. I know a lot of you guys are engineers and tinker types that probably know this stuff.

Thanks for your time. Sorry if I'm on crack for thinking this could work.  All I know is that some people would sh*t themselves if they could have cool flashlight ring that provided enough light to be useful.  As far as making the ring and cramming all the crap inside, no prob, I can do that.  I want the light to shine  parallel to your finger if you were pointing and not straight up.
« Last Edit: April 20, 2013, 03:30 PM by John Welden » Logged
Ca Ike
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« Reply #1 on: April 20, 2013, 04:20 PM »

The MaH rating is usually the capacity of the battery and nothing more.  YOu can use it ti calculate the run life based on what you are using it in.  What you need to be concerned with more than the MaH is the volts.  Led's are rated for specific volts so if you have a .5v LED and a 1.2v battery you will need to add resistance in the circuit to get the final voltage at the LED to .5v so you don't burn out the LED the second you flip the switch.  They do make micro resistors but I don't know of anyplace that carries them.  Might be easier to get the smallest resistor size someplace like radio shack sells and design the ring so you can place the resistors in the band.
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chilese
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« Reply #2 on: April 20, 2013, 04:29 PM »

The problem with resistors is that you are wasting

battery life to heat the resistor, which would heat the ring.

There are circuits that can "chop" the power so that the

LED feels the correct voltage and you won't waste any

power. On the negative side, you now have more

components to put in the ring.

Good luck, Green Lantern.  Smiley
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John Chilese: Las Vegas, NV
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Ca Ike
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« Reply #3 on: April 20, 2013, 04:47 PM »

There are already some flashlight rings out there. Before you start just try to find LED's with a volt rating that matches the battery you plan to use.  There are micro hearing aid batts in small voltages that will negate the need for a fancy circuit. Capacitors can also chop voltages and can help with batt life too.  Batt charges the cap but the cap only released a specific voltage.


« Last Edit: April 20, 2013, 04:50 PM by Ca Ike » Logged
John Welden
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« Reply #4 on: April 20, 2013, 06:41 PM »

Thanks for the help guys.

On the LED website I posted, why wouldn't they list the voltage?

I'm going to try to make this ring so it pretty much looks like a normal band and not a Green Lantern nerd alert deal.  Cheesy
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Ca Ike
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« Reply #5 on: April 20, 2013, 08:37 PM »

Those particular type of LED's they rarely list voltage for.  They are more than likely .3v or less and can handle up to 12v.  THose are what you usually see in TVs or on comp boards as indicator lights so they can handle a good voltage range.
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fidelio
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« Reply #6 on: April 20, 2013, 09:59 PM »

You might begin with disassembling one of these and using the parts as they're bright for their size and are petite for starters.
http://www.amazon.com/gp/product/B0011UIPIW/ref=oh_details_o09_s00_i00?ie=UTF8&psc=1

Otherwise you may find parts of interest here.
Http://dx.com/c/flashlights-lasers-999/flashlight-parts-and-tools-917?pageSize=200



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Fdeli
mikenchico
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« Reply #7 on: April 21, 2013, 05:58 AM »

You should have no problems running an LED off a micro battery without a resistor , all the ones I've checked specs on have a voltage rating of 1 - 3.5 v and you definitely won't be throwing too much current (amperage) at it. Surface mount resistors are tiny if needed.

We were in Lowes yesterday and they had one of those "impulse, while you wait in line" buys called a Frog legs light. A tiny LED Light small enough to stick on a key, or the bezel of a smart phone - I mean tiny, this thing could be painted gold and glued to a band for a ring. Of course I wouldn't expect a Weldon Ring to be that cheesy. But the parts are there including a micro switch for under $3.00

The specs for those LEDs you linked are in the .pdf files, you're safe without a resistor, your problem may be achieving enough voltage and current with a single cell, you'll likely need two to reach the ~ 3v and ~20 mA optimal power range. Unless you were cutting the casing down on those LEDs you linked I would look at the Reverse Mount SMD packaging from the same company. Size is 1.6 x 3.2 MM vrs that 4 x 4 MM you linked and much thinner. Heck you can get down to 1.6 x 0.8 MM in the 0603 package. There are also Low Current bulbs available there which will run off ~ 1.5 v and 10 mA, they might run off a single cell, but they are in the typical 'through the hole mounting with bottom leads so you might have to modify the lens to keep them low enough for a ring.


« Last Edit: April 21, 2013, 07:38 AM by mikenchico » Logged

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John Welden
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« Reply #8 on: April 21, 2013, 10:53 AM »

Thanks you guys for the information, I understand a lot more than I did before. I knew I could come here for help.  Smiley

We are having a lovely spring here in Washington state. Pouring down rain... I guess that leaves time for LED rings..  Roll Eyes
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sluggo
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« Reply #9 on: April 21, 2013, 01:21 PM »

You can calculate the required resistor via: Resistance in ohms = (Battery volts - diode forward voltage) / (diode forward current) or just use an online calculator.

Surface mount resistors might be useful.
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madhabitz
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« Reply #10 on: April 21, 2013, 01:40 PM »

I'll leave the LED stuff to you geeky guys.What I'm interested in is what kind of metal you're going to use. How about some silver? If you use silver (prices are way down right now), I can help you etch it with textures or lineart. This is a really cool project- can't wait to see the end result.
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"I haven't failed. I've just found ten-thousand ways that won't work."   -Thomas Edison
John Welden
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« Reply #11 on: April 21, 2013, 04:45 PM »

I'll leave the LED stuff to you geeky guys.What I'm interested in is what kind of metal you're going to use. How about some silver? If you use silver (prices are way down right now), I can help you etch it with textures or lineart. This is a really cool project- can't wait to see the end result.

They'll most likely be titanium or stainless because I'd machine them from solid material rather than investment cast as you'd do with precious metals.  Silver isn't really hard enough to machine well. 

Thanks for the offer on etching. I might hit you up on a different project.

This project is on the back burner. I just wanted to learn more about LEDs for now.  I'm currently remaking my wife's ring. The first one was a little too fragile and cracked around the hinge.
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WinterDaze
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« Reply #12 on: April 22, 2013, 04:24 AM »

John, not sure if you know of Candlepowerforums but heres a link to their 'homemade' discussions.

If its to do with flashlights that place will know it....
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John Welden
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« Reply #13 on: April 22, 2013, 07:58 AM »

John, not sure if you know of Candlepowerforums but heres a link to their 'homemade' discussions.

If its to do with flashlights that place will know it....


Good idea, ill check them out. 

I didn't even know until about five years ago about the whole flashlight fanatic thing.  The hardest core kite fanatic is nothing compared to the average flashlight collector freak.  So funny... Whatever, to each his own.
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mikenchico
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« Reply #14 on: April 23, 2013, 07:19 AM »

Titanium can be acid etched also if that's what Nancy was referring to, it comes out in nice rainbows & unicorn colors. Almost any metal can be treated with the right acids to achieve differing colors. One of our favorite jewelry makers use of the processes to make some very unique industrial/steampunk type stuff.

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"Living is easy with eyes closed, misunderstanding all you see" John W Lennon

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