Relays and LEDs
 

I was at Radioshack yesterday buying a whole lot of stuff. I saw relays there and wondered how they work. Can I use those to power a pump? Also How would I make a simple circuit to turn on and off (with a switch) a bunch of LEDs?

Relays: it's easier to think of them as "powered switches": you apply power, and they flip a switch.

You don't need a relay to turn on LEDs. How many LEDS anyways?

All you need is a fair DC voltage source (PSU), and the right resistor.

those r two different questions BigBen.

Ok, then...

To answser your first question, I'll refer you to this article

To answer your second question, you need to know the voltage drop across the LEDs that you plan to use (Vled), the voltage that you're going to supply (V), and the current that the LED needs (Iled).

The value of the resistor can be calculated as (V-Vled) / Iled. With that number in hand, you'd pick the next higher up resistor value.

I hope that answers your questions.

Thank you my gracious sire.