Review on Aquacomputer Quadro Fan Controller PWM Fans by Mike Pearson

This controls the fan speed based on the temperature of the water (or whatever you want to soften). It does the job well. It comes with a temperature sensor, but it is meant to be glued onto the component. Since the company appears to be liquid-oriented, I'm surprised they don't offer a submersible probe. But the sensors are relatively cheap, so I used a water temp sensor that I bought separately and screwed it into the secondary tank port. It regulates the water temperature according to a curve on a chart in their software. When the coolant temperature gradually increases, the fan speed gradually increases and the water temperature decreases again. Just like homeostasis, this is an ideal negative feedback mechanism. I found the control software relatively easy to set up. If you've gotten this far into building computers, software shouldn't be a problem for you. Now the fans will not turn on suddenly and unnecessarily when the CPU core temperature rises sharply. This is because they are no longer controlled by CPU temperature, which I felt was a pointless way to go. Yay Quadro!