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Author Topic: little LED problem  (Read 2954 times)

jpantoga

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little LED problem
« on: November 26, 2004, 06:02:08 PM »

I plan on running 5 LEDs for a project I am doing for school.  The only problem is, I am a real electronics noobie, so I have no idea what to do.  I made a little diagram on what I had planned, only I don't know the power of the battery I should use.  I plan on using normal 1.5 or 1.6 v. LED's, nothing too fancy.   Here is a little diagram I drew up, Im sure there are many problems: so please help me.

viridius

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little LED problem
« Reply #1 on: November 26, 2004, 06:09:06 PM »

You have the LEDs in parallel, which is fine.  You'll need a resistor though, and you'll need to know the voltage of the battery to find the resistance.  If you can find the voltage of the battery, use one of the resistance calculators.    In parallel, voltages stay the same and currents add, so sum up the current draw for five LEDs and plug that into the calculator with the voltage for one LED as the forward voltage.
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jpantoga

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little LED problem
« Reply #2 on: November 26, 2004, 06:14:24 PM »

Im trying the online calculator, but I don't know what the desired LED current should be.  It is a little confusing, can anyone clear that up for me?

viridius

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little LED problem
« Reply #3 on: November 26, 2004, 06:15:40 PM »

You usually find that from the packaging of the LED, the reseller's site, or the manufacturer.  There should be a number under "forward current" or "operating current", usually abbreviated as "If" or "Iop".
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Hak Foo

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little LED problem
« Reply #4 on: November 26, 2004, 07:33:34 PM »

If you can't find the current, 10 milliamperes is a good estimate.

For ease and efficiency, perhaps you should consider wiring the LEDs in series.  Only one resistor required.
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john_is_war

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little LED problem
« Reply #5 on: November 26, 2004, 09:29:20 PM »

You only need one resistor if you do them in parallel as well
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jpantoga

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little LED problem
« Reply #6 on: November 27, 2004, 01:16:24 PM »

One more question:  Since I'm using multiple LED's, would it be appropriate just to put one 250 valued resistor in the beginning?  Or will this make it impossible for the other LED's to opperate since there is not enough power?

Alric_the_mad

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little LED problem
« Reply #7 on: November 27, 2004, 09:35:08 PM »

on your diagram, you have your switch in paralell. The only think that'll do is that when it's closed (in the "on" position), it'll dim your LEDs. You need to make the switch either interrupt your ground or supply lines if you want it to turn the LEDs off/on.


edit:
I am stupid when it comes to wiring up LEDs, but I have found that if you use a 10-ohm resistor, you're pretty safe. On the last circuit I built, I used 30 ohms of resistance before an expensive blue LED, on unknown voltage, and it's still running fine.
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jpantoga

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little LED problem
« Reply #8 on: November 27, 2004, 10:45:07 PM »

Ive run into some problems.  The resistors I have been using, although said to be the perfect rating from x24's downloadable calculator, seem to be overheating.  I have already gone through 4 of them.  Is there anyway, without entirely scrapping what I have done so far, to fix this problem?

Entens

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little LED problem
« Reply #9 on: November 27, 2004, 11:33:46 PM »

spread out the area of resistance...
ie if your using 4 resistors, use 8 but inline so you get the same effect as if you used 4. They would in theory heat up half as quick, and be only half as hot. I also could be wrong, someone else confirm what i said.
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