I'm trying to mock up a PWM stir plate. It uses a 555 chip and potentiometer to help control a 12 computer fan. I found a wiring diagram on a homebrew talk forum but I don't know how to transfer a diagram to a prototyping breadboard. I was hoping someone around here could check my work.
Hopefully there are 2 images attached; the diagram and a breadboard mock up.

This uses a 555 timer chip...I don't know anything about the theory, except that it basically turns the fan on/off really fast to control the speed. No idea why the parts were chosen, just trying to recreate it. If anyone has motivation to explain what's going on there I would be grateful. http://i.imgur.com/HOBRHRH.jpg

http://i.imgur.com/0IGuVsb.jpg

Here is a link to the original build. http://www.homebrewtalk.com/f255/simple-pwm-stirplate-controller-219121/