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[AshofRebirth]

I'm not sure if that's the proper term for them... but they are those small circular batteries you usually use for watches and small toys. Those.

Okay so. My first time working with LEDs. Trying to find a way to make a circuit as compact as possible.

I thought I'd ask about this because I've seen this done with toys at least twice now... Some kid at work broke one of our flashing lights toys, which is why I saw it lol But anyway

The way its set up is that there are three watch batteries.. You know what. I'll just draw it:



Yellow thing is the LED. The thick black lines are the prongs. And the gray things are three watch batteries in a row. Just kind of held there.


Is this a efficient to wire an LED..? Does anyone know the typical voltage for each watch battery? I've also seen this same thing but with two LEDs sharing three batteries. The second LED would be on the bottom side.
But anyway.. could anyone tell me about this? Does this way have a decent life..? There are no wires what soever. Just all the metal parts connecting.

[Millions_Knives]

verdatum if there was ever a time for a long answer this would be it
i however dont have that talant
so i hope this link will do

short answer is if you ca n get it to light up just from the leads to some button cells
that seems rather small

[Bisected8]

IIRC most button cells (technically all "batteries" are cells and a battery consists of several connected cells but only D cell and button cell batteries are called them for some reason) are 1.5 volts for small ones (you can also get slightly larger lithium ones called "coin cells" which tend to be 3 volts). Here's a diagram of the different sizes.

As long as you've got the polarity correct, you'll be fine arranging them that way (you can also slide a small piece of paper or plastic in between the cells to act as a switch if you're really hard up for space) but you might have some trouble keeping them in place without some sort of clip...

Button cells last for ages (button and coin cells are designed to provide constant low voltages for long periods of time) and I doubt a single LED's going to tax them much.

[verdatum]

First off, that drawing is NSFW, disgusting, and quite childish. You should be ashamed.

Second, lol Million_Knives, I try not to talk too long about electronics. Arguably, unlike things like resins or prop-painting techniques, there's a fair amount of well written information sources on the web, so it's easier to just link to it.

Anyway, here's what I know:

A standard button battery is generally 1.5v.

When you hook up a second LED with the leads hanging off the other side, that's known as hooking them up "in parallel". You want to avoid this. Instead, you should hook the long end of one LED to the short end of another, then hook the remaining ends to the battery.

In general a proper LED circuit involves a power source, and LED, and a resistor of the appropriate value. As long as your resister is correct, you can use as many batteries as you want, the more batteries, the longer it'll live, that's all.

If you leave the resistor off, it'll often work alright with one or two button batteries, but it may drastically shorten the LED life, particularly with larger batteries.

Read this link carefully before continuing as it starts to get technical: http://www.kpsec.freeuk.com/components/led.htm

Ya gotta do some math to determine what size resistor to use, and if you are using scrounged LEDs, it can be difficult sometimes to figure this out. The best way is to measure it when it's still hooked up to its original device. First in parallel to determine the voltage drop, and then you cut a wire at the first or last LED and hook the multimeter to the two ends to determine what current the device is running it at. Then plug those numbers into the equation given in the above link.

If any part of the link confuses you, ask followup questions!

[AshofRebirth]

Originally Posted by verdatum

First off, that drawing is NSFW, disgusting, and quite childish. You should be ashamed.

I'm not sure if you're serious here, but I apologize anyway. I didn't mean for it to appear so phallic. XD;



Oh and thanks everyone! I think that answered my question.

Followup question though: Each LED has a 3V capacity right(is that even there right word..?). If I did two of the 1.5 v batteries or even the 3V, wouldn't I not need a resistor at all?

[Access]

Originally Posted by AshofRebirth

I'm not sure if you're serious here, but I apologize anyway. I didn't mean for it to appear so phallic. XD;



Oh and thanks everyone! I think that answered my question.

Followup question though: Each LED has a 3V capacity right(is that even there right word..?). If I did two of the 1.5 v batteries or even the 3V, wouldn't I not need a resistor at all?

The activation voltage of the LED varies, reds tend to be around 1.8V, blues can be as high as 3.7V. Other colors tend to be in between these two numbers. Also it changes with temperature, and as the LED ages. For this reason you should almost always use a resistor, unless you are limiting the current in some other fashion (ie. a constant-current driver).

If you do not know what value resistor to use (or you want the circuit to work with any voltage) you can construct a constant current source using the commonly available LM317 integrated circuit (should be able to find one at radio shack, etc.)
http://en.wikipedia.org/w/index.php?...t.svg&pag e=1
http://en.wikipedia.org/wiki/Constan...rent_ sources
(Replace the 100 ohm resistor with a wire. Replace the 1.25 ohm resistor with a resistor between 1K and 100 ohm (less resistance -> brighter LED). The voltage drop across the LM317 will be roughly 3-4V minimum, so use a 9V battery if you choose to use this circuit. The benefit here is the current will stay constant regardless of the voltage of the battery and the LED (or chain of LEDs in series), as long as a battery with a high enough voltage is used. So for instance you could power 6 red LEDs (around 12V) in series with 2x 9V batteries (around 18V) in series.

If you go the series resistor route, start with a value like 1K and see if that is sufficiently bright. If not follow the instructions online and calculate the proper value for the resistor. Most small low-power LEDs can handle up to 20mA without burning up.

There is honestly nothing wrong with wiring LEDs in parallel if it makes sense for the working voltage of the battery you are using (ie. a 3V battery and 1.8V LEDs). Just make sure each LED has its own current-limiting resistor if you choose to do this. The reason people generally prefer to wire in series is because only one resistor is required, and it's easier to string them together.