Led Soldering

[diluzio91]

n__n__n__n_
|   ________|
|  |
|  |
a  b
|  |
|  |
-  +

So I soldered the 4 leds like those above, flat sides are the flat side of the n. my questions are. do i have the +/- correct? And should i put a switch at A or B to turn the leds on and off. Thanks guys.

[blaze15301]

it looks right to me. the switch should be on the positive side.

[slaveofconvention]

Actually it doesn't really matter where the switch goes - it'll work in either location

[crenn]

I hope you're going to be using a current limiting resistor when you use those LEDS on the 12v rail.

[xr4man]

I hope you're going to be using a current limiting resistor when you use those LEDS on the 12v rail.

that depends on the leds he used. you have to know the forward voltage specs to determine the resistor needed.


usually the normal colors (red, yellow, green) are about 1.87 to 2.1 volts. the odd colors (blue, white) are usually 3 to 3.2 volts. add them all up to see how much voltage you are dropping first. then calculate the resistor if needed.

[diluzio91]

i have 4 at 3.2v-3.8v running on a 12v rail, that shouldn't require a resistor right?

[xr4man]

yeah, that should be fine. i think i have a 56 ohm resistor with 3 2v leds on a 12 volt line. either that or maybe it's a 120 ohm resistor, i can't remember now. but you should be fine.

[SXRguyinMA]

You can safely run 4 LEDs off a 12v rail, it'll be fine (as long as they're not red, then you'll need a small resistor). As far as the switch goes typically you put switches on the ground side of things. This is because if you do it on the positive, every time you click that switch on there's a tiny spark, and over time it can corrode the internal contact or carbon it up. I know with the small mA draw of the LEDs this isn't an issue, but for automotive stuff like lights it's the way to go. I'm wired to put switched on the GND sides, so I just do it that way.

[diluzio91]

Thanks guys. I will post pix this weekend of my various projects