With the changes to the layout this year, I have several new 350W SMPS out in the garden. Most have been in fairly large cabinets with some form of passive cooling. This year things have got smaller so I am using some fan forced cooling.But I don't want the fan running all the time.So I have set out to make a simple fan controller.Design Requirement: Operate of 12 Volts Keep fan OFF until needed At 40degree ( this is my first guess) turn the fan ON slowly) At 60degree and above make the fan go flat tack. Between these two set point, the fan speed is to be set proportionally Capable of driving 2x 80mm or 120mm fans The Temperature measurement uses the Dallas DS18S20. I have a number left over from a previous project. So the Prototype is built, the code is finished and the PCB design complete. I hope to get them out to the fab house this week.