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active| newest | oldestI HIGHLY advise against 9v batteries, they are terrible in nearly every way. Cost, total storage, the damn connectors, everything about them.

Pick up a 3 or 4 AAA, AA, C, or D battery holder which outputs either 4.5 or 6v.

"I'm wanting to use 8 3mm blue leds that are 3.4v a piece, 8 3mm yellow that are 2.1v a piece, and 4 red that are 2.1v a piece."

I'll set this up as if you are using a 3series holder, 4.5v:

Source voltage: 4.5v

8x blue 3.4v @ 16mA

8 yellow 2.1 @ 16mA

4 red 2.1 @ 16mA

use this website to do the calculations: http://led.linear1.org/led.wiz

Blue:

Solution 0: 1 x 8 array uses 8 LEDs exactly

+----|>|---/\/\/---- R = 82 ohms

+----|>|---/\/\/---- R = 82 ohms

+----|>|---/\/\/---- R = 82 ohms

+----|>|---/\/\/---- R = 82 ohms

+----|>|---/\/\/---- R = 82 ohms

+----|>|---/\/\/---- R = 82 ohms

+----|>|---/\/\/---- R = 82 ohms

+----|>|---/\/\/---- R = 82 ohms

The wizard says: In solution 0:

each 82 ohm resistor dissipates 20.992 mW

the wizard thinks ¼W resistors are fine for your application

Yellow:

Solution 0: 2 x 4 array uses 8 LEDs exactly

+----|>|----|>|---/\/\/---- R = 22 ohms

+----|>|----|>|---/\/\/---- R = 22 ohms

+----|>|----|>|---/\/\/---- R = 22 ohms

+----|>|----|>|---/\/\/---- R = 22 ohms

The wizard says: In solution 0:

each 22 ohm resistor dissipates 5.632 mW

the wizard thinks ¼W resistors are fine for your application

Red:

Solution 0: 2 x 2 array uses 4 LEDs exactly

+----|>|----|>|---/\/\/---- R = 22 ohms

+----|>|----|>|---/\/\/---- R = 22 ohms

The wizard says: In solution 0:

each 22 ohm resistor dissipates 5.632 mW

the wizard thinks ¼W resistors are fine for your application

the leds are -|>|-

the resistors are -/\/\/- in the pictures

the blues have one resistor per led

the yellows are like the reds, 2 leds, one resistor.

don't worry about cost, they're worth a few cents each. Many ebay led retailers will include free resistors when you buy the leds, just tell them the ohmage you want.

So, imagine every line of my answer above, with 1 or 2 leds with a resistor on each, and ALL the + connections are connected to battery +, ALL the - connections are battery -.

LEDS are polarized, they only go one way, that's what the arrow means.

Resistors can go either way.

Or do you want us guess yelow LED RUNNING uh an 7VDC battery ?

A