Quote:
Originally posted by lynx@29 December 2003 - 13:21
Strange fan speed readings can be one of the drawbacks of pwm speed control.
It generally depends on the fan type. The chip counts the number of times the signal falls to zero. If there is no mechanism to keep the tacho signal high when the pwm signal goes low then the pwn signal will swamp the tacho signal.
A good fan will have a diode and capacitor in its construction in order to keep the supply to the tacho high, but the counters aren't very accurate in any case, because they have a divider on the number of ticks in a certain period, and are then multiplied up to give the rpm.
well, can't expect too much out of a intel stock fan. ;)