If you are planning on using more than a handful of BlinkMs in a project, you will likely find that their $15 price tag quickly adds up. Instructables user [jimthree] found himself in that position and opted to create his own homebrew version of a BlinkM instead. He calls his creations “Ghetto Pixels”, and while they might not look as professional as the real thing, they get the job done just the same.
He bought a batch of RGB LEDs online for under a dollar apiece, pairing them with ATTiny45s that he scored for about $1.50 each. [imthree] popped his uCs into a programmer, flashing them with an open-source BlinkM firmware clone called CYZ_RGB. He then prototyped his circuit on some breadboard, adding the appropriate resistors to the mix before testing out the LEDs. When he was confident everything was working correctly, he assembled Ghetto Pixels deadbug-style.
When everything was said and done, they came together in a pretty compact package comparable to that of the BlinkM. As you can see in the video below, they work great too!