Help with LED flashlight circuit design

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John Welden:
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.

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.

Ca Ike:
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.

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.  :)

Ca Ike:
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.

John Welden:
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.  :D


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