The following page contains detail information regarding the Simple Automatic Fan Controller Circuit Board Design. The PCB measures approximately 1.5 x 3 inches (4.8 x 7.6mm).
Here is a quotation from the original article: “Transistor Q1 can be a 2N2222(A), 2N3904, NTE123A, ECG123A, etc. Not critical at all. It acts only as a switch for the relay so almost any type will work, as long as it can provide the current needed to activate the relay’s coil.” (reference: electronics-lab.com)
http://circuitzoo.com/2010/05/09/electronics/simple-automatic-fan-controller-pcb-circuit-board-design/comment-page-1#comment-60
