Of course, you don't need to limit yourself to only one Ghetto Pixel. The whole point of them is that you can sting a whole bunch of them together. I have built four so far and would have built more, had this instructable not taken so much time to write!
You should still build and test each one in isolation, once you have as many as you need, then you can start playing with them all together.
First off, If you are still using the BlinkM communicator sketch on the arduino, you will need to comment out the line that resets the pixel's address every time the sketch is run. The line is commented, and it's in the setup routine.
You need to change the address of the pixel away from it's default value of 0x09, and you can do this in the sequencer. Plug the first pixel in and set it's address to 0x01, then take it out and plug in the second, give that 0x02, etc. Give each pixel you've made it's own address.
Now you can begin to wire them all up together. This requires nothing but wire, you simply connect up all the pins of the same type among all the pixels. I built a harness with DIP sockets to do this, although you could solder directly onto the pins of the uC, or put them all in perfboard... whatever, it's up to you.
Once linked, you can change the channel number on the left of the BlinkM sequence display for each track to control your pixels individually. Of course, you can code your own programs to send either serial to the communicator sketch or a new sketch entirely that addresses the individual pixels. (If you want to spend all your time playing with the cool BlinkM software tools, then you should be buying real blinkMs!)
I'm going to stop writing now and go and build more pixels. I've got four so far and need another three. I'm building an multichannel extreme feedback device that illuminates a set of seven clear gem dice
. After that I plan to build some more, try and get them solar powered, and string them up in the trees in my garden. I hope you all share your projects too!
Happy making, and Shine on!