1 Design Specifications

To implement a speed control for a common DC brushless fan, the following items are required:

• A 4-wire fan with both a tachometer output and speed control input
• A frequency counter peripheral to measure the tachometer output (fan speed)
• Either an analog drive (0-12V) or a digital PWM (0-12V)
• A Proportional/Integrator/Differentiator (PID) to provide phase/gain compensated feedback