A quick and easy stirrer for mixing culture media, photo chemicals, molecular gastronomy, or what have you...
PWM muffin fan
12v power brick (must be a regulated laptop/dvd player brick, not a cheepo wallwart as the specified PWM controller uses a 555 timer chip with a 12v maximum limit
assorted screws, standoffs, and rubber cushion buttons
PWM controller (got mine from ebay seller ilavmodding as "mini Fan Controller use on 4pin PWM fans only")
plastic enclosure or a square of plexiglass/polycarbonate or other plastic
first glue the magnet to the fan hub and if the fan is from a Dell, put the wires in the right order in the connector (should mate with the 4pin header on the controller module in the following order (viewed from side with trim pot and 4pin header facing you) from left to right: black (-), red (+), yellow (tach), blue (PWM)). Now connect power brick to a three pin connector or the included 3pin cable negative to black and positive to red (with the 3pin header facing you on the controller black will be on the left, red in the middle, and yellow on the right. Use the rubber buttons on the same side of the fan as the magnet (hot glue a piece of plexiglass to the buttons to provide a surface to place a beaker on). use the screws and standoffs on the other side for feet or to mount the fan to a base.
mount the controller to the fan or enclosure, plug in the fan and power brick to the controller and it should run and vary from slow to full speed as the trim pot is adjusted.
You should be able to see/hear the fan speed up and slow down as the controller is adjusted. Need to order some spinbars and labware and start culturing yeast for my next batch of homebrew 8-) (and put the stirrer in an enclosure...) In the mean time, a quick test with a deli cup of water and a minuscule (1/16"x1/16"x1/2") bar magnet shows a nice vortex that threatened to overflow at high speed...