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How to make simple LED color thingo.. (beginner)

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tim_l_012

New Member
Hi All,

This is my first post to the forum, and I was wondering if any of you could help me.

I am making a small device that will sit in the front of my computer case. I currently have a red LED to show that hard drive is thinking, but I would to show green when it is not.

I have been looking at multi-color LED's, and there are 3 legs on the LED. I suspect one for ground, one for red, and one for green.

The motherboard on my computer only has 2 wires, one for power and one for ground. I need to make something that will detect if there is power going into the LED, so that if there isn't, I can enable the green leg, and otherwise the red leg.

If anyone could help me out on this, it would be greatly appreciated.

Thanks in advance, :)

P.S: If you need any more info on what i'm doing, please reply or email me at [email protected].

Thanks again!
 

tim_l_012

New Member
So there is no way I can get some some sort of switch that will enable one circuit if no current is passed into it, and if current is passed into it, it will enable a different circuit?
 

droid

New Member
here's my idea but it would require 2 separate leds..

connect the 2 leds in reverse, the anode of the red to the cathode of the green and the cathode of the red to the anode of the green.. add a limiting resistor..

connect the power line to an inverter (transistor inverter would do)..

now, connect one terminal of the leds/resistor to the power line, the other to the output of the inverter..

how's that?
 

tim_l_012

New Member
OK, is there a electrical component I can use, that will switch off if there if no current, and on if there is a current? EG, the switch will always be off, unless there is a current?

and how can I make the circuit that wont run when the current is applied not run?

is there a device like this?

Thanks in advance, :)
 

daviddoria

New Member
get an PNP transistor.

it is off when there is no current applied to the base and on when there is current.

look up transistors and if you still need help i'll draw a diagram
 

tim_l_012

New Member
If you could provide a diagram of how I would wire it up (or solder it to the PCB), that would be very helpful.

Thanks in advance, :)
 

bogdanfirst

New Member
you can make a circuit but you require another wire, the +5V wire. think this is a problem? if not i can make the schematic.
also, for the 3 leg led you have, the middle is the anode or the cathode?
do you connect it to -- and the other 2 to + to make the led light or you connect the center one to + and the other 2 to -?
please check that with 2 batteries. it is importan to know.
 

tim_l_012

New Member
OK, thanks for your help guys!

The diagram posted in the projects section worked perfectly.

In answer to a few questions:

I did use another circuit, using the power of a 9V battery.
The middle leg of the LED is the common cathode.

Thanks for all of your help on this small project of mine, :D
 

bogdanfirst

New Member
glad your circuit works. hope you enjoy it. does it look nicer now?
but, couldn you use instead of the 9V battery wich might not last as much as if you would have put 2 1.5V bateries, due to its smaller capacity, couldnt you use power from the computer power suply? use the 5V or the 12V?
 

tim_l_012

New Member
Yeah the circuit looks pretty cool now that its all complete.
I blew up the LED a few times, but I worked out I was pumping 12v straight into it, without any resistance.

I eventually ended up using the power from a floppy drive power connector, which seems to be doing the job quite nicely.

Thanks for all of your help in this matter, and I hope my next project goes as smoothly as this one did.

Thanks Again, :)
 
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