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Tri-Color LED Computer Header Problem

M

MotherMGA

Jan 1, 1970
0
Ok. I've built a PC and crammed it into a Nintendo case. What I want
to do is hook up a single Tri-Color LED to my motherboard and mount in
the place where the nintendo has its power LED. The reason I want to
do this is so I can 1) have my power light on when the PC is on and 2)
the LED will flash a different color when the Hard Drive accesses.

The LED is a 4 pin, 3 color LED, of the common annode variety. You can
check it out here:
http://www.superbrightleds.com/TriColor LED.htm
I also have a common cathode LED like that one but I can't think of a
way to make it work with the circuit.

The transistor I'm using is a BC178, which is a PNP. I don't know much
about transistors, so any help would be hot. You can read about it
here:
http://www.farnell.com/datasheets/43469001.pdf

Please refer to this circuit that I have drafted:
http://beta.listingbook.com/~sbbowers/LED Circuit.gif

Looking at the circuit, the two +5V cells and the
two grounds are simply 4 pins on my motherboard header. I labeled the
grounds by the names that are on the header. The switches drawn next
to the grounds are part of the header, which I can't control.
everything else is my circuit. I drew the 4pin LED as 3 separate
LEDs, but the +5V that connects to each in the diagram is really the
single annode on the LED.

I originally hooked it up without the transitor, but I found out that
for some reason the HDLED circuit only measures 2V instead of 5V like
the header is labeled. I tried testing against different 5V pins, but
it always measures 2V. The PWRLED circuit measures 5V the way it
should. The 2V is a problem because the Green and Blue LEDS need
3.5V, and it barely lights when hooked up.

So, my goal is to use the 5V circuit which lights the red, blue and
green leds perfectly, but have a transistor control the circuit that
lights the green & blue LEDs for the HD access. With the transistor
in place, Red lights, but dimly and the blue & green LEDs don't light
at all. I thought I may have confused teh Emmitter/Collector on the
transistor and I swapped them, but it still didn't work.

Am I going about this the wrong way? What can I do to make this work?

Thanks for the help.
Scott.
 
J

John Fields

Jan 1, 1970
0
Ok. I've built a PC and crammed it into a Nintendo case. What I want
to do is hook up a single Tri-Color LED to my motherboard and mount in
the place where the nintendo has its power LED. The reason I want to
do this is so I can 1) have my power light on when the PC is on and 2)
the LED will flash a different color when the Hard Drive accesses.

The LED is a 4 pin, 3 color LED, of the common annode variety. You can
check it out here:
http://www.superbrightleds.com/TriColor LED.htm
I also have a common cathode LED like that one but I can't think of a
way to make it work with the circuit.

The transistor I'm using is a BC178, which is a PNP. I don't know much
about transistors, so any help would be hot. You can read about it
here:
http://www.farnell.com/datasheets/43469001.pdf

Please refer to this circuit that I have drafted:
http://beta.listingbook.com/~sbbowers/LED Circuit.gif

Looking at the circuit, the two +5V cells and the
two grounds are simply 4 pins on my motherboard header. I labeled the
grounds by the names that are on the header. The switches drawn next
to the grounds are part of the header, which I can't control.
everything else is my circuit. I drew the 4pin LED as 3 separate
LEDs, but the +5V that connects to each in the diagram is really the
single annode on the LED.

I originally hooked it up without the transitor, but I found out that
for some reason the HDLED circuit only measures 2V instead of 5V like
the header is labeled. I tried testing against different 5V pins, but
it always measures 2V. The PWRLED circuit measures 5V the way it
should. The 2V is a problem because the Green and Blue LEDS need
3.5V, and it barely lights when hooked up.

So, my goal is to use the 5V circuit which lights the red, blue and
green leds perfectly, but have a transistor control the circuit that
lights the green & blue LEDs for the HD access. With the transistor
in place, Red lights, but dimly and the blue & green LEDs don't light
at all. I thought I may have confused teh Emmitter/Collector on the
transistor and I swapped them, but it still didn't work.

Am I going about this the wrong way? What can I do to make this work?

---
I'm confused by your description but if, as you say, those switch
symbols are on the motherboard and are connected to the ground
symbols, that would indicate to me that when the hard drive's LED
was supposed to turn on the HDLED switch would connect to ground,
and when the POWER LED was supposed to turn on the PWRLED switch
would do the same.

If that's true, then your circuit should look like this:

+5>-----+------+------+
| | |
[75R] [75R] [150R]
| | |
|A |A |A
[BLU] [GRN] [RED]
| | |
HDLED>--+------+ |
|
PWRLED>---------------+

It doesn't make any difference which side of the LED the resistor is
connected to, but note that you need a separate 75 ohm resistor for
each of the red and blue LEDs
 
M

MotherMGA

Jan 1, 1970
0
Thanks John. I was making it more complicated than it needed to be.
your solution worked perfectly. Thanks for your help!

Scott.
 
E

ehsjr

Jan 1, 1970
0
MotherMGA said:
Ok. I've built a PC and crammed it into a Nintendo case. What I want
to do is hook up a single Tri-Color LED to my motherboard and mount in
the place where the nintendo has its power LED. The reason I want to
do this is so I can 1) have my power light on when the PC is on and 2)
the LED will flash a different color when the Hard Drive accesses.

The LED is a 4 pin, 3 color LED, of the common annode variety. You can
check it out here:
http://www.superbrightleds.com/TriColor LED.htm
I also have a common cathode LED like that one but I can't think of a
way to make it work with the circuit.

The transistor I'm using is a BC178, which is a PNP. I don't know much
about transistors, so any help would be hot. You can read about it
here:
http://www.farnell.com/datasheets/43469001.pdf

Please refer to this circuit that I have drafted:
http://beta.listingbook.com/~sbbowers/LED Circuit.gif

Looking at the circuit, the two +5V cells and the
two grounds are simply 4 pins on my motherboard header. I labeled the
grounds by the names that are on the header. The switches drawn next
to the grounds are part of the header, which I can't control.
everything else is my circuit. I drew the 4pin LED as 3 separate
LEDs, but the +5V that connects to each in the diagram is really the
single annode on the LED.

I originally hooked it up without the transitor, but I found out that
for some reason the HDLED circuit only measures 2V instead of 5V like
the header is labeled. I tried testing against different 5V pins, but
it always measures 2V. The PWRLED circuit measures 5V the way it
should. The 2V is a problem because the Green and Blue LEDS need
3.5V, and it barely lights when hooked up.

So, my goal is to use the 5V circuit which lights the red, blue and
green leds perfectly, but have a transistor control the circuit that
lights the green & blue LEDs for the HD access. With the transistor
in place, Red lights, but dimly and the blue & green LEDs don't light
at all. I thought I may have confused teh Emmitter/Collector on the
transistor and I swapped them, but it still didn't work.

Am I going about this the wrong way? What can I do to make this work?

Thanks for the help.
Scott.

John Fields gave you the answer to get your LEDs to light
the way you want - no transistor is needed.

I'll comment on your transistor circuit. It shows a PNP,
as you stated in your post. However, you need an NPN in
that circuit, instead of a PNP. Again, that circuit is
not needed with common anode.

Here's a common cathode circuit, using 2 PNP transistors:

+5 --------------------+-----------+
| |
e/ |
PowerLed ---[2k2R]---| Q1 PNP |
(Gnd) c\ |
| e/
HDLED ---[1kR]---- | ---------| Q2 PNP
(Gnd) | c\
| |
[150R] +--------+
| | |
| [75R] [75R]
| | |
Red\ / Blu\ / Grn\ /
----- ----- -----
| | |
Gnd ------------------+-----------+--------+
 
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