DirtyLude
Well-Known Member
The problem is, the tach signal only works when the power is on.
The tach signal 'on' pulse is actually on for half of the fan rotation and off the other half, so 50% duty cycle based on one fan rotation.
If I use PWM to drive the fan, and connect the tach signal to a timer input on my microcontroller, when the PWM goes low, it shuts off the tach signal, giving false signals.
I'm looking for a way around this problem. Will a low pass filter on the driver PWM smooth out the driver power enough to keep the tach signal up when the PWM is low? Or maybe the same thing on the tach side to filter out the smaller signal drops from the PWM low signals?
The tach signal 'on' pulse is actually on for half of the fan rotation and off the other half, so 50% duty cycle based on one fan rotation.
If I use PWM to drive the fan, and connect the tach signal to a timer input on my microcontroller, when the PWM goes low, it shuts off the tach signal, giving false signals.
I'm looking for a way around this problem. Will a low pass filter on the driver PWM smooth out the driver power enough to keep the tach signal up when the PWM is low? Or maybe the same thing on the tach side to filter out the smaller signal drops from the PWM low signals?