Step 1: Parts Acquisition
-1 Dual Printed Circuit Board
-4 10mm High Brightness LEDs
-4 150 Ohm resistors
-1 PC board terminal
-Either AA or AAA batteries
As you can see, I got most of these things from Radio Shack, but the LEDs I picked up during a 90% off closing sale. The screw terminals were on sale for a dollar and the circuit boards were only a few dollars at full price.
Step 2: Figure Out Your Power Supply
The easiest way to power this would be with 4 AA batteries, and a resistor to drop the supply.
I used this lovely site to help figure out what rating to look for without having to sit and do unwanted, tedious math.
According to the wizard, I need a 150 Ohm resistor on the negative lead of each LED.
Step 3: Assembly
We need to solder our pieces onto the board.
The alteration I made to the diagram was to put the PC terminal on so I could switch between my AAA battery pack and a 9v connector, instead of just committing to the 9v connector all together.
Each LED needs a 150 Ohm resistor soldered to its negative lead. Then I soldered each positive lead to the positive terminal on the screw connector.
Step 4: It Looks Like You're Done
If you don't care for a bare circuit board(I sure don't) then go ahead and prepare to mount it in your case. This is another reason I suggest you use a screw terminal as you can disconnect your power supply and make a small hole in your case as compared to an oversized hole or trying to solder around things.
Step 5: Final Considerations
AA batteries can have twice the milliamp hours of AAA, but are obviously larger.
For this it doesn't really matter since overall the entire board and batteries fit comfortably in the palm of my hand. If you're looking to add more LEDs, keep in mind that each one will add a draw of 20mA.
More lights=Greater draw
Greater draw=Shorter runtime
With the Double A pack, I should be able to get several hours out of this simple circuit.
Thanks for reading, this was my first instructable and I tried to be as detailed as possible. If you have any questions feel free to leave them in the comments section.