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I have a circuit already built. A 3-wire fan which a wire is connected to 12V, a wire is ground, and a wire is connected to a pin of an AVR microcontroller. How can I drive this fan and control its speed?
On the fan is written Brushless DC fan and it is like PC fan.
Since you did not identify the fan in question, we will assume that it is a typical 3-wire example. One wire (typically black) is circuit ground. One wire (typically red) is the +12V power to the motor, and the third wire (perhaps yellow?) is likely the tachometer feedback from the fan. Your controller can monitor the speed of the fan using the pulses from the tachometer feedback signal from the fan. And your controller can change the speed of the fan by pulse-width modulating the power it is sending into the fan.
