Why did you choose to use a 2-pin fan instead of a 3- or 4-pin fan?

Hardware, PWM, and Optics
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Asking for a friend, Jeff Watchorn (staff scientist at the Acceleration Consortium). For context:

I read the source code for the stirring modules and they are doing the same thing using PWM on the RPi to control a 2 wire brushless DC fan. To do that I believe they have that stirring hat module which takes the 3.3V PWM signal and the 5V rail power from the pi and does LLT for controlling the fan. That fan has magnets and a hall sensor, they use a feedback loop to dictate the fan speed.

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Hi @sgbaird

There was no strong reason for using a 2-pin. It is slightly cheaper to use a 2-pin fan and it fits into the design of the existing PWM outputs (2 pin outputs). The hall sensor setup we use is basically what a 3-or 4-pin fan does, too.

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