I have been reading through the sample code for the digital caliber project from NK. The one thing that I don't get is why do you guys need to invert the data and clock signals:

// PIN DEFINITIONS: // PB1 --(inverted) data // PB2 --(inverted) clock

And if you guys inverted the signals, was that ever mentioned in the project description (from the tutorial) or did I just missed it.

Please explain.

Were the inverted signal due to the amplifications from the BJT's?

Nevermind, I figured it out! I studied the bjt from a book and it makes sense now. The data or clock acts as a bias controller and when it's high the PB2 or PB1 will be grounded and becomes low. Logic Inverter!