This video takes you from the basics of how transistors work, right through to more advanced concepts like creating adders, decoders, and ALUs, using the power of abstraction.

In the video embedded below, he shows off a homemade voltage detector circuit that he constructed using a trio of BC547 NPN transistors. The circuit is pretty simple though very useful all the same.

Q1 is a simple PNP transistor acting as a pull-down switch until C1 charges and switches off Q1. That should spin up the SATA drive and then surrender pin 11 for drive activity usage.