The arduino is a MEGA 2560 rev3
I raised a topic yesterday but have since made some progress and unfortunately the forum will not let me delete it.
Im trying to control 4 pin pwm fans that are connected as follows
power +12v
ground common ground
tach pulled up via a resistor to the arduinos 5v and connected to interrupt pin
PWM connected to arduino pwm pin
What I have done is setup PWM on timer 1 on all three ports OC1A(pin 11), OC1B(pin 12) and OC1C(pin 13) at 22khz , and from the serial port I can send a command to the arduino to ask it to change the pwm on port a b or c.
Ive tested the pwm on all three pins using the registers and they work fine and as intended (although some people say that pin 13 is actually attached to timer0 and not timer1) and when I alter the pwm register for a b or c it accelerates or decelerates as expected.
Fan 0 is connected as follows OC1C(pin 13) to the pwm in on fan on and int 0 of tach pin on fan
Fan 1 is connected as follows OC1B(pin 12) to the pwm in on fan and int 1 of tach pin on fan
Im currently only watching the rpm out from fan 0 and when the pwms on OC1B(pin 12) and OC1C(pin 13) are at max everything is fine and rpm reads correct, but if I lower the pwm channel OC1B(pin 12) which is connected to fan1 and not fan0 from anything but max the rpm reading on fan 0 goes crazy and I get nonsense readings back, but as soon as I set it back to max its fine. I can alter pwm channel OC1C(pin 13) without any odd behaviour on the RPM readings though.
What im having seems to be like what was found by the person in this topic PWMs affects interrupt? - Frequently-Asked Questions - Arduino Forum
Does anyone have a clue
I will post code up if needed but im not behind my main pc at the mo.
Trev