I couldn't think of a way to explain all this in one line, so apologies for the slightly vague title.
I've built a PWM Fan Controller for a DIY Laptop Cooling Pad Project. It theoretically works, and I am able to vary the duty cycle and achieve a change in fan speed from about 10% to a 100%.
However, the fan speed only changes when I rotate my Linear 100K Potentiometer to the half-way mark, and it increases really rapidly afterward. Changing which components, if any, would help make the change in speed slower and smoother?
I built this taking reference from an Overclockers.com forum thread about the same thing: http://www.overclockers.com/forums/showthread.php/641111-Building-PWM-Controller-for-4-wires-PWM-fan?p=6473318&viewfull=1#post6473318