Hello guys,
Does anybody know what the facnspecs :
mean by 2 pulses per revolution, tach output. Is there one Hall or 2?
Could be one Hall and two magnets or one magnet and two Halls. Does it matter?
Hey John, nice to hear from you.
The problem is that i want to know exactly how many times per revolution an output signal is send from the tach. I think that there is one hall and one magnet, and the first pulse is the start and the second the end, so 2 pulses/rev. Using this info i can get a math model of the fan, which in turn i will use to make a pid controller.
If you have any ideas on my Hall problem, please let me know 
Mircea.
PS: sorry for my English, not my first language
The spec doesn't say how long each pulse is but I believe they mean two full pulses per revolution LOW HIGH LOW HIGH. Make sure you use a pull-up resistor because it's an open-collector output (only drags the line down to 0v, won't supply +v).