Thread: LED Help

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As a newbie, I'm trying my hand at some LEDs that a friend gave me. He won a lot off Ebay and they came with resistors. They are not individual LEDs but attached in a string as shown in the picture.




I'm planning on wiring 5 at a time since they are different colors. How can I tell which lead is the positive and which side is the negative? I plan on using a 9V battery.

Any suggestions on how to do this? Is there a better way than using a 9V battery?

Thanks!

All LED's have a flat part on one side of the actual light part. What ever side that flat part is on, that lead is the negative side.

Your LEDs are individuals, they're just taped together. Assuming each LED needs 3 - 3.5 volts at 20mA, wiring 5 of them in series won't work, the 9 volt battery doesn't have enough voltage to light all of them. Wiring in parallel is the way to go if you want to use that many LEDs. Here's a calculator that will help you choose the resistors and shows the wiring layout. Just plug in your values and click.

LED series parallel array wizard

Thanks NTX JX and Otaku! So if I wire 5 in parallel with a 9v battery, could I use the 470 ohm resistor that comes with them? Here are the specs. Thanks!

Emitted Color White Red Blue Green Orange ---
Lens Color Water Clear ---
Size 5.0 mm
Peak Wave Length --- nm
Forward Voltage 2.0~3.4 V
View Angle About 25° °
Luminous Intensity 4000~15000 mcd
Max Continues Current 25 mA
Max Peak Current 75 mA
Operating Temperature -40~+85 °C