PWM or Pulse Width Modulation has generally been regarded as too complicated for PC fan speed control compared against using rheostats or linear voltage regulators such as the LM317.

For the Brits among us, Maplin Electronics (our RatShack) have a new module, code RN41UView image ...

NesteQ MaxZero 8-Channel Fan Controller / Temperature Monitor While the plugs on the controller are all 3 prong (I believe), they come with the PWM 4-prong adapters.

Of course, you can also skip the PWM code and just use the timer interrupts for timing. It isn’t that the timer code or PWM isn’t workable without a tool.

If you've got an Arduino of any variety, you might have noticed some of the pins on the board have a tilde mark or PWM printed next to them. What is PWM?