Reading the rpm of multiple fans

Question

I am trying to build a fan controller for my pc, the problem is that the example code(http://playground.arduino.cc/Main/ReadingRPM) im using utilizes interrupts. On my uno I can then only read the rpm of one fan. I want to also control the rpm (via pwm) and monitor temperatures (via thermistors) Anyone know how I coud do it differently? I. E. Without interrupts. I would also like it to be as close to real time as possible

Answer 1

If temperature regulation is what you seek, why bother with the Tachometer signal at all?

Thermistors don't require interrupts. Why do you need fully closed loop fan control? A simple proportional control of each fan and each hot item would likely suffice in keeping your system cool. Noise concerns, perhaps?

A brief article on proportional temperature control

A data sheet on a TI chip that may have some inspiration for you

Answer 2

If you only want 2 fans, the uno has 2 external interrupts, so you can use the same strategy as your example, just make another interrupt function for fan 2 and attach it on interrupt 1 instead of 0. the fan should be plugged in to pin 3 in this case. On a leonardo, you could have 5 fans on interrupts, and a mega has 6 external interrupts. See http://arduino.cc/en/Reference/attachInterrupt

If you need more than what your hardware can support, I would look into using a timed interrupt to check all the fans. If you find the minimum amount of time in-between reads to read your fans at max RPM and then use a timer interrupt to check some pins at that interval, you can probably read as many as you need, provided the interrupt routine stays fast enough. the function

attachInterrupt(function, period);

from the libraries on this page : http://playground.arduino.cc/Code/Timer1 should help you out with this.