Need Intro to LEDs...

[nrgy]

I am going to first start off and say I have very limited knowledge with electronics. I simply want to power a led, which will later be applied to a subwoofer project.

My first question is, if I want to simply test a bunch of leds just to see the color output, what's the easiest way to do this? (keeping in mind I need 1st grade education on this).

Secondly, I would like to add an led to the front my subwoofer project for when the subwoofer receives a signal from the receiver, and is essentially on/running. This seems like a simple task, but from searching the boards this seems more difficult than I aniticpated. Any instructions?

Lastly, I remember seeing some very small rectangular/square leds, perhaps 1mm x 2mm. Anyone know a source for these?

Thanks in advance.

[dangus]

Well, it's hard to avoid Ohm's Law when figuring out the resistor to use with an LED. R=V/I where V is the voltage to drop across the resistor, and I is the current.

10 mA is a good rule of thumb to run most LEDs at, although they'll generally survice double that. 10mA = 0.010 amps

The voltage across the LED depends on what colour it is. Red LEDs run at around 1.6V; other colours need more. Unless you're trying to run from a very low voltage supply like 3.3 volts this won't affect things much.

So, if you have a 12 volt power supply, subtract 2 volts to allow for the LED operating voltage, and you have 10 volts to drop in the resistor. R=V/I= 10V/0.01 amps= 1000 ohms.

At higher voltages you'll need to worry about the power dissipated in the resistor. With a 25 volt drop at 10 mA, the resistor would dissipate 1/4 of a watt, so you'd want to use a 1/2 watt resistor. (Power=Volts x Amps)

Flat side of the LED is the negative lead.

To easily test LEDs, get a 9V battery and put a 1k resistor in series to limit the current.

The Wikipedia should have good explanations of concepts like Ohm's Law and Series connections. Series, parallel, and Ohm's Law will take you a long way in understanding electrical circuits.