BlinkM RGB LEDs, strategizing

      Words of caution from Leah (Lady Ada) whose way-oldschool Turn Signal Biking Jacket I am using for some guidance now that I'm at a sewing stage. (On a side note, I wanted to make this jacket SO badly two years ago, but at the time the label "beginner project" seemed kind of unfair.)

As you design, plan to keep your power supply and LilyPad main board close to each other. If they are too far apart, you are likely to have problems with your LilyPad resetting or just not working at all.

Why? Conductive thread has non-trivial resistance. (The 4-ply silver-coated thread from SparkFun that comes with the LilyPad starter kit has about 14 ohms/foot.) Depending on what modules you're using in your construction, your LilyPad can draw up to 50 milliamps (mA) of current, or .05 Amps. Ohm's law says that the voltage drop across a conductive material--the amount of voltage that you lose as electricity moves through the material--is equal to the resistance of the conductive material times the amount of current that is flowing through it.

For example, if your LilyPad is a foot away from the power supply, the total resistance of the conductive material that attaches your LilyPad to your power supply is about 28 ohms. (14 Ohms in the conductive thread that leads from the negative terminal of the power supply to the negative petal on the LilyPad and 14 Ohms in the conductive thread that ties the positive terminals together). This means we can expect a drop of 1.4 Volts (28 Ohms * .05 Amps.) This means that while 5 Volts is coming out of the power supply, the LilyPad will only be getting 3.6 Volts (5 Volts - 1.4 Volts). Once the voltage at the LilyPad drops below about 3.3 Volts, it will reset. The resistance of the traces from + on the power supply to + on the LilyPad and - on the power supply to - on the LilyPad should be at most 10 Ohms. Plan the distance accordingly.

      This presents a new problem to solve, as I was considering hiding the power supply/meter circuit board in a fanny pack...

also, look at THIS and THIS

      These are the LEDs I'm working with. As you can see, they are "smart." Meaning they are integrated into a little circuit board with it's own microcontroller.
      I'm going to remove the pins from the bottom so I can sew directly through the holes. Also, I am going to try puting the LEDs on one side of the fabric and the board on the other. This will look MUCH better.