I finally finished an article on building a PWM (Pulse Width Modulation) controlled stir plate: PWM stir plate design. Building the control logic was a fun project for me since building electronic circuits was a hobby of mine before I got a job in the computer industry. Many years after I build my first stir plate I once again looked into building a stir plate because needed more stir plates for the yeast starter experiments I’m doing. I knew I needed better fan speed control than using linear voltage controller since it was really hard to control the fan speed in my old stir plate design. PWM control does work much better but takes a few more parts and soldering skills.