# Help with LEDs and simple circuits?

Okay, I'm making a little LED project and I'd like help on these following questions:
1. On most switches there are three little prongs, which ones do I connect to which wires?
2. Do I need a resistor for a simple, battery powered, LED circuit, with 16 LEDs? If so, what kind of battery do I need and what kind of resistor?
3. Can LEDs shine through a thin layer (3-5 mm) of balsa wood?
Thanks!
-popewill

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5 years ago
1. Depends on the switch:
The 3 prongs may be 'normally open' 'normally closed' and 'common'
or they may be 'common' 'light' 'normally something', where light lights up the switch.
Generally on a 3 prong, the switch will flop between connecting "common" and NC to connecting "common" to NO"
If you want it to default be on except when pushed, use NC
if you want it to default be off, use NO.

http://en.wikipedia.org/wiki/Switch -- look at 'single pole double throw' to see how the connection works as a diagram

2. Yes, you need a resistor for most conceivable simple circuits, with the exception of button cell (watch battery) circuits because they limit their own current.
If you don't want to learn ohm's law and do a pile of math someone made a wizard just for you:
http://led.linear1.org/led.wiz
You need to know the following information from your LEDS:
Forward voltage, a number between 1.8(infrared), 2 (red), 3(green) and 4.2(blue/white) -- check your spec sheet to be sure!!! It will be called Vf.
Forward current, for MOST cheap 5mm leds it's 20mA as a safe number.
Supply voltage -- the total from your batteries. Don't use 9v batteries, they suck. I recommend 2-4AA batteries in a holder for balance between cost/power.
Number of leds you want.

3. LEDs should shine through balsa, but not extremely bright. Drill the hole as CLOSE to the surface as possible (~1-2mm) without going through. Easy to do with a drill press and an end stop. If you don't have an end-stop then wrap tape around the drill bit to mark the exact depth. Test on a spare piece to get it right before starting :D
popewill (author)  frollard5 years ago
Okay, I have a problem. when I add up the total voltage number it makes 46.2. Is that a little high? Also is it alright if I connect the LEDs directly to each other? because the diagram said to have a resistor with each one. Thanks!
5 years ago
do exactly what the diagram says. don't add up the numbers to enter into the wizard, it will do that part.

example numbers
16 leds
6v source
20ma
3v each

**per your statement, if you put all the leds in series, 16 in a row, you'd need 46 volts, yes. by making smaller strings, each with resistors, you lower the voltage requirements and each string draws more current rather than voltage.
popewill (author)  frollard5 years ago
Ohhhhhhh! I see. Thanks!
popewill (author)  frollard5 years ago
Thanks!