This is to show you how to setup RGB leds to generate any color you want.Parts Needed3 - 1000 Ohm Potentiometers (ten turn type)
3 - 180 to 220 Ohm resistors 1/4 watt or 1/2 watt
1 - RGB Led
Small piece of breadboard for soldering you parts to
Tools NeededSoldering Iron
Multi-Meter
Terminology
The back end of the diode is the Anode (think of it as the backside or ass).
The front of the diode is the Cathode.
Power flows from the back to the front.
So the back of the diode (anode) is always hooked to power.
RGB diodes are sold as either common anode or common cathode
What that means is all the anodes or all the cathodes are tied together
inside the surface mount device. This is the kind of device you want
because there are only four pins on them.
There is another kind of RGB diode that brings out all the pins so you have
a six pin device. This makes it bigger and harder to mod with.
Most of the RGB leds want to run at about 3 volts and 20 ma of current.
You can push them to the limit of 3.8 volts but that shortens the life of them
and really does not give you that much more light.
So we will design to it, using the 3.3 volt supply works just fine for us
so we do not have to reduce the voltage to our leds.
We are only interested in the 20 milli amperes our leds want.
Using Ohms law we can calculate that the 20 ma is achieved by using this formula
Resistance = Voltage / Current
Therefor
Resistance = 3.3 volts / 20 ma (.020 amps)
So the minimum resistance is 150 ohms.
The potentiometers are adjustable but one of the problems with them is you
can adjust the resistance to zero ohms.
If we did that even by accident we would burn up our leds.
So the test circuit puts 180 to 220 ohm resistors in series so
our adjustments can never reach zero.
The cathode side of our leds we are going to hook to ground.
With all this said here is the schematic for the circuit.
You see the fixed resistors in series with our potentiometers (pots)
for safety.
Now you can apply power to light up the RGB led,
Turn each pot slowly from one end to the other and you will see
each color get brighter and darker.
If you do each one in turn you see three colors Red, Green, Blue
If you turn each pot 5 turns or mid range what color do you get ?
So by balancing the all three pots you can mix the three colors and get
any color of the rainbow you want.
Keep adjusting to you get exactly the color you want.
Find your color ?
Turn off the circuit.
Now remove the power source.
Take your meter and measure the resistance from the diode to ground on
each of your colors of the led.
These will be the resistors you need to hook to your rgb led to get the
color you just mixed.
The closer you get to the value you measure, the truer the color will
be to what you adjusted for.
Doing this simple adjustment procedure you can now have any color of leds
you want for your mod. Hook them up just as you would if you have only a
single led.
Caution: Remember because you are using three leds in one, you are using the
power of three leds.
TroubleshootingIf your meter does not get a resistance greater than the series resistor
you will have to separate the ground side of the resistors from each other
to get a more accurate measurement.
If you get a resistance you just can't find say 250 ohms you can
take a 220 ohm and 22 ohm wire them in series (end to end) and you
will have 242 ohms. Most of the resistors we use are 5% so 5% of
250 is 12.5 and 250 - 12 = 238 ohms. So this method will get you
very close and give you the color you adjusted for.
Parts SourceYou can get some of these rgb leds at:
http://cgi.ebay.com/New-50X-SMD-SMT-PLCC-4-MultiColor-RGB-LED-Freeship_W0QQitemZ250076116499QQcmdZViewItem?_trksid=p3286.m20.l1116These are plcc-4 four pin common cathode rgb leds
Really great for modding.
You are buying 50 of them for $21.00 and shipping is included free.
