Physical interaction design DH2400

Problem
The cheap RGB LEDs aren't exactly even in colour. The red can be much brighter than the green and blue or vice versa.

Solution
There's a simple fix for this. Just use different resistors for each colour. One way to determine what resistors you should get is to try first with potentiometers, preferably one with high granularity (depending on how your LED's are connected, you will need different values).

Our setup was 9 LED's connected in parallell per resistor which means that the combined resistance should be about ~5 Ohms according to some guide we found online (google for LED calculator). We had three of these ELFA 64-721-61. They can be rotated 20 times from ~0 to ~200 Ohm which gives you a resolution about 10 Ohms per rotation. It was enough to get the values we were looking for (although in retrospect we should have gone with the 0–50 Ohms for even higher resolution).

Just hook all the LED's up and put the resistor between the current and the LED's and start screwing. Use some simple switches to turn each colour off as you try to match their respective brightness.

When the brightness is to your liking, just measure the resistance of each potentiometer to find out what regular resistors you should use in your circuits.