Led

pumpkinsoftruth · 05-27-2006, 04:12 PM

Anyone know what this type of LED is called, it seems it has 3 pins instead of just the anode and cathode. Also, all 3 pins have a little bulge in the middle of them. Anyone know how I could hook this up to a power source too? Whats the third middle pin for?

**UncleMacro** · 05-27-2006, 06:49 PM

That's just a dual-color LED. It has two LEDs in it which can be turned on independently. I have some which are red/green. The middle pin is usually the shared anode or cathode. You'll have to test it to see which it is.

pumpkinsoftruth · 05-27-2006, 07:19 PM

Does the middle one have to be connected then if I am (for example) connecting it to a battery?

**Terrister** · 05-27-2006, 07:30 PM

You will have to connect the middle and one of the outside. If that does not work, reverse the wires(polarity).

pumpkinsoftruth · 05-27-2006, 07:51 PM

cant seem to get it to work...

I have two cables with one end tied to the left pin and one to the middle and each cable to the battery. I have also tried the same with one on the right pin and one on the middle. I have also tried the one cable over both the left and middle and one over the right and vice versa. I make sure to try both sides of the battery (which is almost full power) to make sure it isn't just a + and - issue. What am I doing wrong?

what battery do you think I should use?

**Terrister** · 05-27-2006, 08:09 PM

See if you can find your answer here.
http://members.misty.com/don/ledfaq.html

pumpkinsoftruth · 05-28-2006, 11:56 AM

That link didn't help too much but thanks anyways. The led is blue/orange.

I just decided it would be better to hook it up to a psu since batteries didn't provide enough power. The standby cable on the 20-pin motherboard connector carries 5 volts. Just using some cable, I put one end of the cable on the pin for the 5 volts and the other end to the positive side of the led with the other cable going from a ground pin to the negative side (the shared middle one). It works great but I am slightly afraid that long term operation might kill the LED because I have no resistor set up in this little circuit. How necessary is a resistor, especially if the LED isn't full powered?

**UncleMacro** · 05-28-2006, 02:34 PM

Running without a resistor is a no no unless you're using a power source with limited current output. A PC power supply can definitely fry LEDs without resistors. The resistor matters but it's value is only critical if you're trying to run the LED at it's maximum current. If you're running both LEDs at the same time then you need to reduce the maximum current because both LEDs are in the same package and it will heat up faster with both of them on. If you don't have resistors laying around then Fry's carries them. Otherwise you should be able to get them at Radio Shack. You can get them anywhere on the Internet but the shipping will cost way more than the resistors. This page gives you plenty of detail on how to pick a resistor.

Keep in mind that the blue side has a forward voltage of about 3.5 volts whereas the orange is about 2 volts. If you're running only one of the two LEDs at a time then 20 milliamps is a reasonable current limit. So if you hook them to 5 volts then that would give you 75 ohms for the blue LED's resistor and 150 ohms (which is two 75 ohms resistors wired in series) for the orange one. Just keep in mind that the resistance value isn't all the critical. You can increase it a little (like say to 100 and 200 ohms) and the LEDs will still be bright.

pumpkinsoftruth · 05-28-2006, 07:30 PM

Hmm I seem to become confused when resistors are involved. So I need one 75 ohm resistor right? I only run the blue, the pin for the orange is not going to be connected.

**UncleMacro** · 05-29-2006, 06:04 AM

Yea. To run one blue LED all you need to do is:

connect 5 volts to one end of the 75 ohm resistor,
connect the other end of the resistor to the positive end of the LED,
connect the negative end of the LED to ground.

Assuming average values for your blue LED it will run at 20 milliamps. It's easy to get whatever resistors you want at good electronic places but at a Radio Shack you may be limited to "standard" values like 68 ohms or 100 ohms. 68 ohms will give you about 22 milliamps which is fine. 100 ohms would give you 15 milliamps which is a little less bright but will still look okay.

pumpkinsoftruth · 05-29-2006, 08:03 AM

Alright thank you for the help. For some reason one thing I saw said I needed to connect the resistor to the negative side, but that didn't seem to make sense.

**UncleMacro** · 05-29-2006, 04:29 PM

Yea, you can hook the resistor to either side. I just wrote it down on the positive side (which is where I usually hook it) and probably half of the other people explaining how to do it hook it to the negative side. The only thing which matters is making sure the LED polarity is correct otherwise it won't turn on.

05-27-2006, 04:12 PM	#1 (permalink)
pumpkinsoftruth Registered User Join Date: Oct 2005 Posts: 19 OS: XP	Led Anyone know what this type of LED is called, it seems it has 3 pins instead of just the anode and cathode. Also, all 3 pins have a little bulge in the middle of them. Anyone know how I could hook this up to a power source too? Whats the third middle pin for?

05-27-2006, 07:30 PM	#4 (permalink)
Terrister Moderator Hardware Forum Join Date: Apr 2005 Location: West Georgia, USA Posts: 7,098 OS: Xp	You will have to connect the middle and one of the outside. If that does not work, reverse the wires(polarity). __________________

05-27-2006, 07:51 PM	#5 (permalink)
pumpkinsoftruth Registered User Join Date: Oct 2005 Posts: 19 OS: XP	cant seem to get it to work... I have two cables with one end tied to the left pin and one to the middle and each cable to the battery. I have also tried the same with one on the right pin and one on the middle. I have also tried the one cable over both the left and middle and one over the right and vice versa. I make sure to try both sides of the battery (which is almost full power) to make sure it isn't just a + and - issue. What am I doing wrong? what battery do you think I should use? Last edited by pumpkinsoftruth; 05-27-2006 at 08:05 PM.

05-27-2006, 08:09 PM	#6 (permalink)
Terrister Moderator Hardware Forum Join Date: Apr 2005 Location: West Georgia, USA Posts: 7,098 OS: Xp	See if you can find your answer here. http://members.misty.com/don/ledfaq.html __________________

05-28-2006, 11:56 AM	#7 (permalink)
pumpkinsoftruth Registered User Join Date: Oct 2005 Posts: 19 OS: XP	That link didn't help too much but thanks anyways. The led is blue/orange. I just decided it would be better to hook it up to a psu since batteries didn't provide enough power. The standby cable on the 20-pin motherboard connector carries 5 volts. Just using some cable, I put one end of the cable on the pin for the 5 volts and the other end to the positive side of the led with the other cable going from a ground pin to the negative side (the shared middle one). It works great but I am slightly afraid that long term operation might kill the LED because I have no resistor set up in this little circuit. How necessary is a resistor, especially if the LED isn't full powered? Last edited by pumpkinsoftruth; 05-28-2006 at 11:58 AM.

05-27-2006, 06:49 PM	#2 (permalink)
UncleMacro TSF Enthusiast Join Date: Jan 2005 Location: San Diego Posts: 2,133 OS: Vista SP1 My System	That's just a dual-color LED. It has two LEDs in it which can be turned on independently. I have some which are red/green. The middle pin is usually the shared anode or cathode. You'll have to test it to see which it is.

05-27-2006, 07:19 PM	#3 (permalink)
pumpkinsoftruth Registered User Join Date: Oct 2005 Posts: 19 OS: XP	Does the middle one have to be connected then if I am (for example) connecting it to a battery?

05-28-2006, 02:34 PM	#8 (permalink)
UncleMacro TSF Enthusiast Join Date: Jan 2005 Location: San Diego Posts: 2,133 OS: Vista SP1 My System	Running without a resistor is a no no unless you're using a power source with limited current output. A PC power supply can definitely fry LEDs without resistors. The resistor matters but it's value is only critical if you're trying to run the LED at it's maximum current. If you're running both LEDs at the same time then you need to reduce the maximum current because both LEDs are in the same package and it will heat up faster with both of them on. If you don't have resistors laying around then Fry's carries them. Otherwise you should be able to get them at Radio Shack. You can get them anywhere on the Internet but the shipping will cost way more than the resistors. This page gives you plenty of detail on how to pick a resistor. Keep in mind that the blue side has a forward voltage of about 3.5 volts whereas the orange is about 2 volts. If you're running only one of the two LEDs at a time then 20 milliamps is a reasonable current limit. So if you hook them to 5 volts then that would give you 75 ohms for the blue LED's resistor and 150 ohms (which is two 75 ohms resistors wired in series) for the orange one. Just keep in mind that the resistance value isn't all the critical. You can increase it a little (like say to 100 and 200 ohms) and the LEDs will still be bright. Last edited by UncleMacro; 05-28-2006 at 02:48 PM.

05-28-2006, 07:30 PM	#9 (permalink)
pumpkinsoftruth Registered User Join Date: Oct 2005 Posts: 19 OS: XP	Hmm I seem to become confused when resistors are involved. So I need one 75 ohm resistor right? I only run the blue, the pin for the orange is not going to be connected.

05-29-2006, 06:04 AM	#10 (permalink)
UncleMacro TSF Enthusiast Join Date: Jan 2005 Location: San Diego Posts: 2,133 OS: Vista SP1 My System	Yea. To run one blue LED all you need to do is: connect 5 volts to one end of the 75 ohm resistor, connect the other end of the resistor to the positive end of the LED, connect the negative end of the LED to ground. Assuming average values for your blue LED it will run at 20 milliamps. It's easy to get whatever resistors you want at good electronic places but at a Radio Shack you may be limited to "standard" values like 68 ohms or 100 ohms. 68 ohms will give you about 22 milliamps which is fine. 100 ohms would give you 15 milliamps which is a little less bright but will still look okay.

05-29-2006, 08:03 AM	#11 (permalink)
pumpkinsoftruth Registered User Join Date: Oct 2005 Posts: 19 OS: XP	Alright thank you for the help. For some reason one thing I saw said I needed to connect the resistor to the negative side, but that didn't seem to make sense.

05-29-2006, 04:29 PM	#12 (permalink)
UncleMacro TSF Enthusiast Join Date: Jan 2005 Location: San Diego Posts: 2,133 OS: Vista SP1 My System	Yea, you can hook the resistor to either side. I just wrote it down on the positive side (which is where I usually hook it) and probably half of the other people explaining how to do it hook it to the negative side. The only thing which matters is making sure the LED polarity is correct otherwise it won't turn on.