LED question

cyber mouse45 · May 6, 2002

Hey, I’m getting ready to start planning where all the wires are going to go in my case, and I have a question. How do I hook a switch, LED and fan up? I want the led to come on when the fan is on, and go off when the fan is off. I’ve never done this before, so I don’t know what to do. Here’s a pic of the parts that I have. Do I need any more parts? I don’t have the switches yet, but I’ll be getting them soon.

Is it possible to have a green LED come on when the fan is on, and a red one when it’s off?
Thanks so much for your help!

Iron Hawk · May 6, 2002

With a SPDT (on-on) switch it is very easy to setup a red-green led. You can buy Bi colored Leds (leds that light up 2 colors) that have 3 leads, one for ground and the others for lighting the different colors. You will need some resistors to lower the voltage for the leds the resistor depends on the voltage and current rating of the led.

Iron Hawk · May 6, 2002

The squiggly things are the resistors

cyber mouse45 · May 6, 2002

Iron Hawk said:
With a SPDT (on-on) switch it is very easy to setup a red-green led. You can buy Bi colored Leds (leds that light up 2 colors) that have 3 leads, one for ground and the others for lighting the different colors. You will need some resistors to lower the voltage for the leds the resistor depends on the voltage and current rating of the led.

Wow, I didn't know I could do that. I’ve never used one before in my life, so could you tell me what sort of resistor I would need for this LED? Thanks!!!!

Iron Hawk · May 6, 2002

ok, here are the stats for that LED

30mA max (lets say 25mA (.025A) so we are not burning this sucker at max)

2 VDC typical

v=i*r therefore r=v/i

r=(12-2)/.025

r=400

so somewhere around 400ohms

I would recomend 390ohms, but not less than 320
Resistors can be added together in series if you cannot find the exact rating.

cyber mouse45 · May 6, 2002

1/2W or 1/4W like these? How do I add two together? Do I just put one right in front of the other?

cyber mouse45 · May 6, 2002

Oh now this stinks. Radioshack doesn’t have any of the right switches in stock.

Iron Hawk · May 7, 2002

cyber mouse45 said:
1/2W or 1/4W like these? How do I add two together? Do I just put one right in front of the other?

1/4 watt is fine, the 1/4 watt value is just a small resistor, it doesn't matter whether you use 1/4 watt, 1/2 watt, etc. The LED doesn't care.

Yes you put them in line (series) and you add the resistance of the two to find the total resistance.

RadioShack never has all of the parts you need

cyber mouse45 · May 8, 2002

Thanks a lot Iron Hawk! You've been a big help.

Iron Hawk · May 8, 2002

No problem, did you get it all to work as you wanted?

cyber mouse45 · May 8, 2002

I just ordered the resistors from RadioShack yesterday, and I need to find someone that sells the right kind of switch too. I'll let ya know how it all works out.

Crazy Jayhawk · May 8, 2002

cyber mouse45 said:
I just ordered the resistors from RadioShack yesterday, and I need to find someone that sells the right kind of switch too. I'll let ya know how it all works out.

You might try a hardware store too. Look in the electrical section.

Iron Hawk · May 8, 2002

DPDT switches will work also, aslong as they are on-on (not on-off-on)

cyber mouse45 · May 8, 2002

Hey Iron Hawk, I have a quick question for ya. What’s that little line there? Is it a wire? Thanks.

Iron Hawk · May 8, 2002

the box with the dotted line is a SPDT switch, that little thing is just part of the drawing.

The black dot is where electricity flows in, and depending on the switch setting, flows out thru one of the white dots.

cyber mouse45 · May 8, 2002

Oh yeah, I see it now. Thanks.

cyber mouse45 · May 14, 2002

Hey Iron Hawk, I have one more question for ya. I have a few led’s that I found but I have no idea where they came from. I think I’d like to use them, but I don’t know what resistor to use. What do I do?

Iron Hawk · May 14, 2002

Most leds are 20mA and depending on colour and voltage their voltage ranges from 2-4 volts (assuem it is 2)

so 20mA, 2volts is what I assume most leds are, try to look up the item on radioshack.com if you want to try to find the exact info.

If you want to attach leds in series, visit this site for an excelent calculator that tells what resistor to use: http://ourworld.compuserve.com/homepages/Bill_Bowden/led.htm

craigiz1 · May 14, 2002

Try www.grainger.com for your switch.

cyber mouse45 · May 14, 2002

Thanks a lot man. That site has some really good stuff on it.

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